PYLINT(1)

NAME
pylint - Pylint Documentation Pypi Package versionDocumentation Statuspre-commit.ci statusCII Best PracticesOpenSSF ScorecardDiscord.SH WHAT IS PYLINT?

Pylint is a static code analyser for Python 2 or 3. The latest version supports Python 3.7.2 and above.

Pylint analyses your code without actually running it. It checks for errors, enforces a coding standard, looks for code smells, and can make suggestions about how the code could be refactored.

INSTALL

For command line use, pylint is installed with:

pip install pylint

Or if you want to also check spelling with enchant (you might need to install the enchant C library):

pip install pylint[spelling]

It can also be integrated in most editors or IDEs. More information can be found in the documentation.

WHAT DIFFERENTIATE PYLINT?

Pylint is not trusting your typing and is inferring the actual value of nodes (for a start because there was no typing when pylint started off) using its internal code representation (astroid). If your code is import logging as argparse, Pylint can check and know that argparse.error(...) is in fact a logging call and not an argparse call. This makes pylint slower, but it also let pylint find more issues if your code is not fully typed. [inference] is the killer feature that keeps us using [pylint] in our project despite how painfully slow it is. - Realist pylint user, 2022

pylint, not afraid of being a little slower than it already is, is also a lot more thorough than other linters. There is more checks, some opinionated one that are deactivated by default, but can be enabled using configuration.

HOW TO USE PYLINT

Pylint isn't smarter than you: it may warn you about things that you have conscientiously done or check for some things that you don't care about. During adoption, especially in a legacy project where pylint was never enforced, it's best to start with the --errors-only flag, then disable convention and refactor message with --disable=C,R and progressively re-evaluate and re-enable messages as your priorities evolve.

Pylint is highly configurable and permits to write plugins in order to add your own checks (for example, for internal libraries or an internal rule). Pylint also has an ecosystem of existing plugins for popular frameworks and third party libraries.

NOTE: Pylint supports the Python standard library out of the box. Third-party libraries are not always supported, so a plugin might be needed. A good place to start is PyPI which often returns a plugin by searching for pylint <library>. pylint-pydantic, pylint-django and pylint-sonarjson are examples of such plugins. More information about plugins and how to load them can be found at plugins.

ADVISED LINTERS ALONGSIDE PYLINT

Projects that you might want to use alongside pylint include ruff (really fast, with builtin auto-fix, and a growing number of checks taken from popular linters but implemented in rust) or flake8 (faster and simpler checks with very few false positives), mypy, pyright or pyre (typing checks), bandit (security oriented checks), black and isort (auto-formatting), autoflake (automated removal of unused imports or variables), pyupgrade (automated upgrade to newer python syntax) and pydocstringformatter (automated pep257).

ADDITIONAL TOOLS INCLUDED IN PYLINT

Pylint ships with two additional tools:

•   pyreverse (standalone tool that generates package and class diagrams.)

•   symilar (duplicate code finder that is also integrated in pylint)

CONTRIBUTING

We welcome all forms of contributions such as updates for documentation, new code, checking issues for duplicates or telling us that we can close them, confirming that issues still exist, creating issues because you found a bug or want a feature, etc. Everything is much appreciated!

Please follow the code of conduct and check the Contributor Guides if you want to make a code contribution.

SHOW YOUR USAGE

You can place this badge in your README to let others know your project uses pylint. .UNINDENT

Learn how to add a badge to your documentation in the the badge documentation.

LICENSE

pylint is, with a few exceptions listed below, GPLv2.

The icon files are licensed under the CC BY-SA 4.0 license:

•   doc/logo.png

•   doc/logo.svg

SUPPORT

Please check the contact information.
[image: Tidelift] [image] | Professional support for pylint is available as part of the Tidelift Subscription. Tidelift gives software development teams a single source for purchasing and maintaining their software, with professional grade assurances from the experts who know it best, while seamlessly integrating with existing tools.

  Tutorial

This tutorial is all about approaching coding standards with little or no knowledge of in-depth programming or the code standards themselves. It's the equivalent of skipping the manual and jumping right in.

The command line prompt for these examples is:

tutor Desktop$

  Getting Started

Running Pylint with the --help arguments will give you an idea of the arguments available. Do that now, i.e.:

pylint --help

A couple of the options that we'll focus on here are:

Commands:
  --help-msg=<msg-id>
  --generate-toml-config
Messages control:
  --disable=<msg-ids>
Reports:
  --reports=<y or n>
  --output-format=<format>

If you need more detail, you can also ask for an even longer help message:

pylint --long-help

Pay attention to the last bit of this longer help output. This gives you a hint of what Pylint is going to pick on:

Output:
   Using the default text output, the message format is :
  MESSAGE_TYPE: LINE_NUM:[OBJECT:] MESSAGE
  There are 5 kind of message types :
  * (C) convention, for programming standard violation
  * (R) refactor, for bad code smell
  * (W) warning, for python specific problems
  * (E) error, for probable bugs in the code
  * (F) fatal, if an error occurred which prevented pylint from doing
  further processing.

When Pylint is first run on a fresh piece of code, a common complaint is that it is too noisy. The default configuration enforce a lot of warnings. We'll use some of the options we noted above to make it suit your preferences a bit better.

  Your First Pylint'ing

We'll use a basic Python script with black already applied on it, as fodder for our tutorial. The starting code we will use is called simplecaesar.py and is here in its entirety:

#!/usr/bin/env python3
import string
shift = 3
choice = input("would you like to encode or decode?")
word = input("Please enter text")
letters = string.ascii_letters + string.punctuation + string.digits
encoded = ""
if choice == "encode":
    for letter in word:
        if letter == " ":
            encoded = encoded + " "
        else:
            x = letters.index(letter) + shift
            encoded = encoded + letters[x]
if choice == "decode":
    for letter in word:
        if letter == " ":
            encoded = encoded + " "
        else:
            x = letters.index(letter) - shift
            encoded = encoded + letters[x]
print(encoded)

Let's get started. If we run this:

tutor Desktop$ pylint simplecaesar.py
************* Module simplecaesar
simplecaesar.py:1:0: C0114: Missing module docstring (missing-module-docstring)
simplecaesar.py:5:0: C0103: Constant name "shift" doesn't conform to UPPER_CASE naming style (invalid-name)
simplecaesar.py:8:0: C0103: Constant name "letters" doesn't conform to UPPER_CASE naming style (invalid-name)
simplecaesar.py:9:0: C0103: Constant name "encoded" doesn't conform to UPPER_CASE naming style (invalid-name)
simplecaesar.py:13:12: C0103: Constant name "encoded" doesn't conform to UPPER_CASE naming style (invalid-name)
simplecaesar.py:15:12: C0103: Constant name "x" doesn't conform to UPPER_CASE naming style (invalid-name)
simplecaesar.py:16:12: C0103: Constant name "encoded" doesn't conform to UPPER_CASE naming style (invalid-name)
simplecaesar.py:20:12: C0103: Constant name "encoded" doesn't conform to UPPER_CASE naming style (invalid-name)
simplecaesar.py:22:12: C0103: Constant name "x" doesn't conform to UPPER_CASE naming style (invalid-name)
simplecaesar.py:23:12: C0103: Constant name "encoded" doesn't conform to UPPER_CASE naming style (invalid-name)
-----------------------------------
Your code has been rated at 4.74/10

We can see the second line is:

"simplecaesar.py:1:0: C0114: Missing module docstring (missing-module-docstring)"

This basically means that line 1 at column 0 violates the convention C0114. Another piece of information is the message symbol between parens, missing-module-docstring.

If we want to read up a bit more about that, we can go back to the command line and try this:

tutor Desktop$ pylint --help-msg=missing-module-docstring
:missing-module-docstring (C0114): *Missing module docstring*
  Used when a module has no docstring.Empty modules do not require a docstring.
  This message belongs to the basic checker.

That one was a bit of a no-brainer, but we can also run into error messages where we are unfamiliar with the underlying code theory.

  The Next Step

Now that we got some configuration stuff out of the way, let's see what we can do with the remaining warnings. If we add a docstring to describe what the code is meant to do that will help. There are invalid-name messages that we will get to later. Here is the updated code:

#!/usr/bin/env python3
"""This script prompts a user to enter a message to encode or decode
using a classic Caesar shift substitution (3 letter shift)"""
import string
shift = 3
choice = input("would you like to encode or decode?")
word = input("Please enter text")
letters = string.ascii_letters + string.punctuation + string.digits
encoded = ""
if choice == "encode":
    for letter in word:
        if letter == " ":
            encoded = encoded + " "
        else:
            x = letters.index(letter) + shift
            encoded = encoded + letters[x]
if choice == "decode":
    for letter in word:
        if letter == " ":
            encoded = encoded + " "
        else:
            x = letters.index(letter) - shift
            encoded = encoded + letters[x]
print(encoded)

Here is what happens when we run it:

tutor Desktop$ pylint simplecaesar.py
************* Module simplecaesar
simplecaesar.py:8:0: C0103: Constant name "shift" doesn't conform to UPPER_CASE naming style (invalid-name)
simplecaesar.py:11:0: C0103: Constant name "letters" doesn't conform to UPPER_CASE naming style (invalid-name)
simplecaesar.py:12:0: C0103: Constant name "encoded" doesn't conform to UPPER_CASE naming style (invalid-name)
simplecaesar.py:16:12: C0103: Constant name "encoded" doesn't conform to UPPER_CASE naming style (invalid-name)
simplecaesar.py:18:12: C0103: Constant name "x" doesn't conform to UPPER_CASE naming style (invalid-name)
simplecaesar.py:19:12: C0103: Constant name "encoded" doesn't conform to UPPER_CASE naming style (invalid-name)
simplecaesar.py:23:12: C0103: Constant name "encoded" doesn't conform to UPPER_CASE naming style (invalid-name)
simplecaesar.py:25:12: C0103: Constant name "x" doesn't conform to UPPER_CASE naming style (invalid-name)
simplecaesar.py:26:12: C0103: Constant name "encoded" doesn't conform to UPPER_CASE naming style (invalid-name)
------------------------------------------------------------------
Your code has been rated at 5.26/10 (previous run: 4.74/10, +0.53)

Nice! Pylint told us how much our code rating has improved since our last run, and we're down to just the invalid-name messages.

There are fairly well defined conventions around naming things like instance variables, functions, classes, etc. The conventions focus on the use of UPPERCASE and lowercase as well as the characters that separate multiple words in the name. This lends itself well to checking via a regular expression, thus the should match (([A-Z_][A-Z1-9_]*)|(__.*__))$.

In this case Pylint is telling us that those variables appear to be constants and should be all UPPERCASE. This is an in-house convention that has lived with Pylint since its inception. You too can create your own in-house naming conventions but for the purpose of this tutorial, we want to stick to the PEP 8 standard. In this case, the variables we declared should follow the convention of all lowercase. The appropriate rule would be something like: "should match [a-z_][a-z0-9_]{2,30}$". Notice the lowercase letters in the regular expression (a-z versus A-Z).

If we run that rule using a --const-rgx='[a-z\_][a-z0-9\_]{2,30}$' option, it will now be quite quiet:

tutor Desktop$ pylint simplecaesar.py --const-rgx='[a-z\_][a-z0-9\_]{2,30}$'
************* Module simplecaesar
simplecaesar.py:18:12: C0103: Constant name "x" doesn't conform to '[a-z\\_][a-z0-9\\_]{2,30}$' pattern (invalid-name)
simplecaesar.py:25:12: C0103: Constant name "x" doesn't conform to '[a-z\\_][a-z0-9\\_]{2,30}$' pattern (invalid-name)
------------------------------------------------------------------
Your code has been rated at 8.95/10 (previous run: 5.26/10, +3.68)

You can read up on regular expressions or use a website to help you.

TIP: It would really be a pain to specify that regex on the command line all the time, particularly if we're using many other options. That's what a configuration file is for. We can configure our Pylint to store our options for us so we don't have to declare them on the command line. Using a configuration file is a nice way of formalizing your rules and quickly sharing them with others. Invoking pylint --generate-toml-config will create a sample .toml section with all the options set and explained in comments. This can then be added to your pyproject.toml file or any other .toml file pointed to with the --rcfile option.

  Installation

Pylint can be installed:

•   As a command line tool

•   Integrated in your editor/ide

•   As a pre-commit hook

•   For multiple python interpreters in your continuous integration

  Command line installation

Pylint is installable using a package manager. Your package manager will find a version that works with your interpreter. We recommend pip:

pip install pylint

Or if you want to also check spelling with enchant (you might need to install the enchant C library):

pip install pylint[spelling]

The newest pylint supports all Python interpreters that are not past end of life.

We recommend to use the latest interpreter because we rely on the ast builtin module that gets better with each new Python interpreter. For example a Python 3.6 interpreter can't analyse 3.8 syntax (amongst others, because of the new walrus operator) while a 3.8 interpreter can also deal with Python 3.6. See using pylint with multiple interpreters for more details.

NOTE: You can also use conda or your system package manager on debian based OS. These package managers lag a little behind as they are maintained by a separate entity on a slower release cycle.

conda install pylint

sudo apt-get install pylint

  Editor and IDE integration

Pylint can be integrated in various editors and IDE's. Below you can find tutorials for some of the most common ones.

•   Eclipse

•   Emacs

•   Eric IDE in the Project > Check menu,

•   gedit (another option for gedit)

•   Flymake

•   Jupyter Notebook

•   Komodo

•   Pycharm

•   PyDev

•   pyscripter in the Tool -> Tools menu.

•   Spyder in the View -> Panes -> Static code analysis

•   Sublime Text

•   TextMate

•   Vim

•   Visual Studio Code in the Preferences -> Settings menu

•   Visual Studio Code Pylint Extension

•   Visual Studio in the Python > Run PyLint command on a project's context menu.

•   WingIDE

  Using Pylint through Flymake in Emacs

WARNING: The Emacs package now has its own repository and is looking for a maintainer. If you're reading this doc and are interested in maintaining this package or are actually using flymake please open an issue at https://github.com/emacsorphanage/pylint/issues/new/choose

To enable Flymake for Python, insert the following into your .emacs:

;; Configure Flymake for Python
(when (load "flymake" t)
  (defun flymake-pylint-init ()
    (let* ((temp-file (flymake-init-create-temp-buffer-copy
                       'flymake-create-temp-inplace))
           (local-file (file-relative-name
                        temp-file
                        (file-name-directory buffer-file-name))))
      (list "epylint" (list local-file))))
  (add-to-list 'flymake-allowed-file-name-masks
               '("\\.py\\'" flymake-pylint-init)))
;; Set as a minor mode for Python
(add-hook 'python-mode-hook '(lambda () (flymake-mode)))

Above stuff is in pylint/elisp/pylint-flymake.el, which should be automatically installed on Debian systems, in which cases you don't have to put it in your .emacs file.

Other things you may find useful to set:

;; Configure to wait a bit longer after edits before starting
(setq-default flymake-no-changes-timeout '3)
;; Keymaps to navigate to the errors
(add-hook 'python-mode-hook '(lambda () (define-key python-mode-map "\C-cn" 'flymake-goto-next-error)))
(add-hook 'python-mode-hook '(lambda () (define-key python-mode-map "\C-cp" 'flymake-goto-prev-error)))

Finally, by default Flymake only displays the extra information about the error when you hover the mouse over the highlighted line. The following will use the minibuffer to display messages when you the cursor is on the line.

;; To avoid having to mouse hover for the error message, these functions make Flymake error messages
;; appear in the minibuffer
(defun show-fly-err-at-point ()
  "If the cursor is sitting on a Flymake error, display the message in the minibuffer"
  (require 'cl)
  (interactive)
  (let ((line-no (line-number-at-pos)))
    (dolist (elem flymake-err-info)
      (if (eq (car elem) line-no)
      (let ((err (car (second elem))))
        (message "%s" (flymake-ler-text err)))))))
(add-hook 'post-command-hook 'show-fly-err-at-point)

Alternative, if you only wish to pollute the minibuffer after an explicit flymake-goto-* then use the following instead of a post-command-hook

(defadvice flymake-goto-next-error (after display-message activate compile)
  "Display the error in the mini-buffer rather than having to mouse over it"
  (show-fly-err-at-point))
(defadvice flymake-goto-prev-error (after display-message activate compile)
  "Display the error in the mini-buffer rather than having to mouse over it"
  (show-fly-err-at-point))

  Integrate Pylint with TextMate

Install Pylint in the usual way:

pip install pylint

Install the Python bundle for TextMate:

1.  select TextMate > Preferences

2.  select the Bundles tab

3.  find and tick the Python bundle in the list

    You should now see it in Bundles > Python.

    In Preferences, select the Variables tab. If a TM_PYCHECKER variable is not already listed, add it, with the value pylint.

    The default keyboard shortcut to run the syntax checker is Control-Shift-V - open a .py file in Textmate, and try it.

    You should see the output in a new window: PyCheckMate 1.2 – Pylint 1.4.4

    No config file found, using default configuration

    Then all is well, and most likely Pylint will have expressed some opinions about your Python code (or will exit with 0 if your code already conforms to its expectations).

    If you receive a message: Please install PyChecker, PyFlakes, Pylint, PEP 8 or flake8 for more extensive code checking.

    That means that Pylint wasn't found, which is likely an issue with command paths - TextMate needs be looking for Pylint on the right paths.

    Check where Pylint has been installed, using which:

    $ which pylint
    /usr/local/bin/pylint

    The output will tell you where Pylint can be found; in this case, in /usr/local/bin.

1.  select TextMate > Preferences

2.  select the Variables tab

3.  find and check that a PATH variable exists, and that it contains the appropriate path (if the path to Pylint were /usr/local/bin/pylint as above, then the variable would need to contain /usr/local/bin). An actual example in this case might be $PATH:/opt/local/bin:/usr/local/bin:/usr/texbin, which includes other paths.

    ... and try running Pylint again.

  Pre-commit integration

pylint can be used as a pre-commit hook.

Since pylint needs to import modules and dependencies to work correctly, the hook only works with a local installation of pylint (in your environment). If you installed pylint locally it can be added to .pre-commit-config.yaml as follows:

- repo: local
  hooks:
    - id: pylint
      name: pylint
      entry: pylint
      language: system
      types: [python]
      args:
        [
          "-rn", # Only display messages
          "-sn", # Don't display the score
        ]

You can use args to pass command line arguments as described in the Tutorial. A hook with more arguments could look something like this:

- repo: local
  hooks:
    - id: pylint
      name: pylint
      entry: pylint
      language: system
      types: [python]
      args:
        [
          "-rn", # Only display messages
          "-sn", # Don't display the score
          "--rcfile=pylintrc", # Link to your config file
          "--load-plugins=pylint.extensions.docparams", # Load an extension
        ]

  Installation with multiple interpreters

It's possible to analyse code written for older or multiple interpreters by using the py-version option and setting it to the oldest supported interpreter of your code. For example you can check that there are no f-strings in Python 3.5 code using Python 3.8 with an up-to-date pylint even if Python 3.5 is past end of life (EOL) and the version of pylint you use is not compatible with it.

We do not guarantee that py-version will work for all EOL Python interpreters indefinitely, (for anything before Python 3.5, it probably won't). If a newer version does not work for you, the best available pylint might be an old version that works with your old interpreter but without the bug fixes and features of later versions.

  Show your usage

You can place this badge in your README to let others know your project uses pylint. .UNINDENT

Use the badge in your project's README.md (or any other Markdown file):

[![linting: pylint](https://img.shields.io/badge/linting-pylint-yellowgreen)](https://github.com/PyCQA/pylint)

Use the badge in your project's README.rst (or any other rst file):

.. image:: https://img.shields.io/badge/linting-pylint-yellowgreen
    :target: https://github.com/PyCQA/pylint

If you use GitHub Actions, and one of your CI workflows begins with "name: pylint", you can use GitHub's workflow status badges to show an up-to-date indication of whether pushes to your default branch pass pylint. For more detailed information, check the documentation.

  Upgrading pylint

You should probably set the version of pylint in your development environment in order to choose when you actually upgrade pylint's warnings. pylint is following semver versioning. But we can't guarantee that the output between version will stays the same. What this means is that:

•   In patch release (1.2.3), we only fix false positives and crashes.

    You can expect less messages if you set the minor and upgrade to a new patch version. But still, if you enable useless-suppression it still means you can get a new useless-suppression when a false positive that you disabled is now fixed. Also, if a library you're using was upgraded and is understood better or worse than the previous one, you could get new messages too.

•   In minor releases (1.2.0), we add checks, remove checks, drop python interpreters past end of life, upgrade astroid minor/major versions and fix false negatives.

    You can expect a lot more change in output, the main one being new checks.

•   In major releases (1.0.0) we change everything else (pylint options, json output, dev API...) while still trying to minimize disruption.

    You could have to change the command you're launching or the plugin and editor integration you're using.

  Usage

  Running Pylint

  On module packages or directories

Pylint is meant to be called from the command line. The usage is

pylint [options] modules_or_packages

By default the pylint command only accepts a list of python modules and packages. On versions below 2.15, specifying a directory that is not an explicit package (with __init__.py) results in an error:

pylint mydir
************* Module mydir
mydir/__init__.py:1:0: F0010: error while code parsing: Unable to load file mydir/__init__.py:
[Errno 2] No such file or directory: 'mydir/__init__.py' (parse-error)

Thus, on versions before 2.15, or when dealing with certain edge cases that have not yet been solved, using the --recursive=y option allows for linting a namespace package:

pylint --recursive=y mydir mymodule mypackage

This option makes pylint attempt to discover all modules (files ending with .py extension) and all explicit packages (all directories containing a __init__.py file).

Pylint will not import this package or module, but it does use Python internals to locate them and as such is subject to the same rules and configuration. You should pay attention to your PYTHONPATH, since it is a common error to analyze an installed version of a module instead of the development version.

  On files

It is also possible to analyze Python files, with a few restrictions. As a convenience, you can give it a file name if it's possible to guess a module name from the file's path using the python path. Some examples:

pylint mymodule.py should always work since the current working directory is automatically added on top of the python path

pylint directory/mymodule.py will work if: directory is a python package (i.e. has an __init__.py file), an implicit namespace package or if directory is in the python path.

  With implicit namespace packages

If the analyzed sources use implicit namespace packages (PEP 420), the source root(s) should be specified using the --source-roots option. Otherwise, the package names are detected incorrectly, since implicit namespace packages don't contain an __init__.py.

  Globbing support

It is also possible to specify both directories and files using globbing patterns:

pylint [options] packages/*/src

  Command line options

First of all, we have two basic (but useful) options.

--version
    show program's version number and exit

-h, --help
    show help about the command line options

    Pylint is architected around several checkers. You can disable a specific checker or some of its messages or message categories by specifying --disable=<symbol>. If you want to enable only some checkers or some message symbols, first use --disable=all then --enable=<symbol> with <symbol> being a comma-separated list of checker names and message symbols. See the list of available features for a description of provided checkers with their functionalities. The --disable and --enable options can be used with comma-separated lists mixing checkers, message ids and categories like -d C,W,no-error,design

    It is possible to disable all messages with --disable=all. This is useful to enable only a few checkers or a few messages by first disabling everything, and then re-enabling only what you need.

    Each checker has some specific options, which can take either a yes/no value, an integer, a python regular expression, or a comma-separated list of values (which are generally used to override a regular expression in special cases). For a full list of options, use --help

    Specifying all the options suitable for your setup and coding standards can be tedious, so it is possible to use a configuration file to specify the default values. You can specify a configuration file on the command line using the --rcfile option. Otherwise, Pylint searches for a configuration file in the following order and uses the first one it finds:

1.  pylintrc in the current working directory

2.  .pylintrc in the current working directory

3.  pyproject.toml in the current working directory, providing it has at least one tool.pylint. section. The pyproject.toml must prepend section names with tool.pylint., for example [tool.pylint.'MESSAGES CONTROL']. They can also be passed in on the command line.

4.  setup.cfg in the current working directory, providing it has at least one pylint. section

5.  tox.ini in the current working directory, providing it has at least one pylint. section

6.  If the current working directory is in a Python package, Pylint searches up the hierarchy of Python packages until it finds a pylintrc file. This allows you to specify coding standards on a module-by-module basis. Of course, a directory is judged to be a Python package if it contains an __init__.py file.

7.  The file named by environment variable PYLINTRC

8.  if you have a home directory which isn't /root:

1.  .pylintrc in your home directory

2.  .config/pylintrc in your home directory

9.  /etc/pylintrc

    The --generate-toml-config option will generate a commented configuration file on standard output according to the current configuration and exit. This includes:

•   Any configuration file found as explained above

•   Options appearing before --generate-toml-config on the Pylint command line

    Of course you can also start with the default values and hand-tune the configuration.

    Other useful global options include:

--ignore=<file[,file...]>
    Files or directories to be skipped. They should be base names, not paths.

--output-format=<format>
    Select output format (text, json, custom).

--msg-template=<template>
    Modify text output message template.

--list-msgs
    Generate pylint's messages.

--list-msgs-enabled
    Display a list of what messages are enabled and disabled with the given configuration.

--full-documentation
    Generate pylint's full documentation, in reST format.

  Parallel execution

It is possible to speed up the execution of Pylint. If the running computer has more CPUs than one, then the work for checking all files could be spread across all cores via Pylints's sub-processes. This functionality is exposed via the -j command-line parameter. If the provided number is 0, then the total number of CPUs will be autodetected and used.

Example:

pylint -j 4 mymodule1.py mymodule2.py mymodule3.py mymodule4.py

This will spawn 4 parallel Pylint sub-process, where each provided module will be checked in parallel. Discovered problems by checkers are not displayed immediately. They are shown just after checking a module is complete.

There are some limitations in running checks in parallel in the current implementation. It is not possible to use custom plugins (i.e. --load-plugins option), nor it is not possible to use initialization hooks (i.e. the --init-hook option).

  Exit codes

Pylint returns bit-encoded exit codes.
exit code | meaning
0 | no error
1 | fatal message issued
2 | error message issued
4 | warning message issued
8 | refactor message issued
16 | convention message issued
32 | usage error

For example, an exit code of 20 means there was at least one warning message (4) and at least one convention message (16) and nothing else.

  Pylint output

  Output options

Output by default is written to stdout. The simplest way to output to a file is with the --output=<filename> option.

The default format for the output is raw text. You can change this by passing pylint the --output-format=<value> option. Possible values are: text, json, parseable, colorized and msvs (for Visual Studio).

Multiple output formats can be used at the same time by passing a comma-separated list of formats to --output-format. This output can be redirected to a file by giving a filename after a colon.

For example, to save a json report to somefile.json and print a colorized report to stdout at the same time:

--output-format=json:somefile.json,colorized

  Custom message formats

You can customize the exact way information are displayed using the --msg-template=<format string> option. The format string uses the Python new format syntax and the following fields are available :

path
    relative path to the file

abspath
    absolute path to the file

line
    line number

column
    column number

end_line
    line number of the end of the node

end_column
    column number of the end of the node

module
    module name

obj object within the module (if any)

msg text of the message

msg_id
    the message code (eg. I0011)

symbol
    symbolic name of the message (eg. locally-disabled)

C   one letter indication of the message category

category
    fullname of the message category

    For example, the former (pre 1.0) default format can be obtained with:

    pylint --msg-template='{msg_id}:{line:3d},{column}: {obj}: {msg}'

    A few other examples:

•   the default format:

    {path}:{line}:{column}: {msg_id}: {msg} ({symbol})

•   Visual Studio compatible format (former 'msvs' output format):

    {path}({line}): [{msg_id}{obj}] {msg}

•   Parseable (Emacs and all, former 'parseable' output format) format:

    {path}:{line}: [{msg_id}({symbol}), {obj}] {msg}

    The --msg-template option can only be combined with text-based reporters (--output-format either unspecified or one of: parseable, colorized or msvs). If both --output-format and --msg-template are specified, the --msg-template option will take precedence over the default line format defined by the reporter class.

    If end_line or end_column are None, they will be represented as an empty string by the default TextReporter.

  Source code analysis section

For each python module, Pylint will first display a few '*' characters followed by the name of the module. Then, a number of messages with the following format:

MESSAGE_TYPE: LINE_NUM:[OBJECT:] MESSAGE

You can get another output format, useful since it's recognized by most editors or other development tools using the --output-format=parseable option.

The message type can be:

•   [I]nformational messages that Pylint emits (do not contribute to your analysis score)

•   [R]efactor for a "good practice" metric violation

•   [C]onvention for coding standard violation

•   [W]arning for stylistic problems, or minor programming issues

•   [E]rror for important programming issues (i.e. most probably bug)

•   [F]atal for errors which prevented further processing

    Sometimes the line of code which caused the error is displayed with a caret pointing to the error. This may be generalized in future versions of Pylint.

    Example (extracted from a run of Pylint on itself...):

    ************* Module pylint.checkers.format
    W: 50: Too long line (86/80)
    W:108: Operator not followed by a space
         print >>sys.stderr, 'Unable to match %r', line
                ^
    W:141: Too long line (81/80)
    W: 74:searchall: Unreachable code
    W:171:FormatChecker.process_tokens: Redefining built-in (type)
    W:150:FormatChecker.process_tokens: Too many local variables (20/15)
    W:150:FormatChecker.process_tokens: Too many branches (13/12)

  Reports section

Following the analysis message, Pylint can display a set of reports, each one focusing on a particular aspect of the project, such as number of messages by categories, modules dependencies. These features can be enabled through the --reports=y option, or its shorthand version -ry.

For instance, the metrics report displays summaries gathered from the current run.

•   the number of processed modules

•   for each module, the percentage of errors and warnings

•   the total number of errors and warnings

•   percentage of classes, functions and modules with docstrings, and a comparison from the previous run

•   percentage of classes, functions and modules with correct name (according to the coding standard), and a comparison from the previous run

•   a list of external dependencies found in the code, and where they appear

  Score section

Finally, Pylint displays a global evaluation score for the code, rated out of a maximum score of 10.0. This output can be suppressed through the --score=n option, or its shorthand version -sn.

The evaluation formula can be overridden with the --evaluation=<python_expression> option.

  Messages

  Messages overview

Pylint can emit the following messages:

  Fatal

All messages in the fatal category:

  astroid-error / F0002

Message emitted:

%s: %s

Description:

Used when an unexpected error occurred while building the Astroid representation. This is usually accompanied by a traceback. Please report such errors !

Additional details:

This is a message linked to an internal problem in pylint. There's nothing to change in your code, but maybe in pylint's configuration or installation.

Created by the main checker.

  config-parse-error / F0011

Message emitted:

error while parsing the configuration: %s

Description:

Used when an exception occurred while parsing a pylint configuration file.

Additional details:

This is a message linked to a problem in your configuration not your code.

Created by the main checker.

  fatal / F0001

Message emitted:

%s

Description:

Used when an error occurred preventing the analysis of a module (unable to find it for instance).

Additional details:

This is a message linked to an internal problem in pylint. There's nothing to change in your code.

Created by the main checker.

  method-check-failed / F0202

Message emitted:

Unable to check methods signature (%s / %s)

Description:

Used when Pylint has been unable to check methods signature compatibility for an unexpected reason. Please report this kind if you don't make sense of it.

Additional details:

This is a message linked to an internal problem in pylint. There's nothing to change in your code.

Created by the classes checker.

  parse-error / F0010

Message emitted:

error while code parsing: %s

Description:

Used when an exception occurred while building the Astroid representation which could be handled by astroid.

Additional details:

This is a message linked to an internal problem in pylint. There's nothing to change in your code.

Created by the main checker.

All renamed messages in the fatal category:

  old-import-error / F0401

'old-import-error' has been renamed. The new message can be found at:

  import-error / E0401

Message emitted:

Unable to import %s

Description:

Used when pylint has been unable to import a module.

Problematic code:

from patlib import Path  # [import-error]

Correct code:

from pathlib import Path

Additional details:

This can happen if you're importing a package that is not installed in your environment, or if you made a typo.

The solution is to install the package via pip/setup.py/wheel or fix the typo.

Created by the imports checker.

  Error

All messages in the error category:

  abstract-class-instantiated / E0110

Message emitted:

Abstract class %r with abstract methods instantiated

Description:

Used when an abstract class with `abc.ABCMeta` as metaclass has abstract methods and is instantiated.

Problematic code:

import abc
class Animal(abc.ABC):
    @abc.abstractmethod
    def make_sound(self):
        pass
sheep = Animal()  # [abstract-class-instantiated]

Correct code:

import abc
class Animal(abc.ABC):
    @abc.abstractmethod
    def make_sound(self):
        pass
class Sheep(Animal):
    def make_sound(self):
        print("bhaaaaa")
sheep = Sheep()

Created by the basic checker.

  access-member-before-definition / E0203

Message emitted:

Access to member %r before its definition line %s

Description:

Used when an instance member is accessed before it's actually assigned.

Problematic code:

class Foo:
    def __init__(self, param):
        if self.param:  # [access-member-before-definition]
            pass
        self.param = param

Correct code:

class Foo:
    def __init__(self, param):
        self.param = param
        if self.param:
            pass

Created by the classes checker.

  assigning-non-slot / E0237

Message emitted:

Assigning to attribute %r not defined in class slots

Description:

Used when assigning to an attribute not defined in the class slots.

Problematic code:

class Student:
    __slots__ = ('name',)
    def __init__(self, name, surname):
        self.name = name
        self.surname = surname  # [assigning-non-slot]
        self.setup()
    def setup(self):
        pass

Correct code:

class Student:
    __slots__ = ('name', 'surname')
    def __init__(self, name, surname):
        self.name = name
        self.surname = surname
        self.setup()
    def setup(self):
        pass

Created by the classes checker.

  assignment-from-no-return / E1111

Message emitted:

Assigning result of a function call, where the function has no return

Description:

Used when an assignment is done on a function call but the inferred function doesn't return anything.

Problematic code:

def add(x, y):
    print(x + y)
value = add(10, 10)  # [assignment-from-no-return]

Correct code:

def add(x, y):
    return x + y
value = add(10, 10)

Created by the typecheck checker.

  assignment-from-none / E1128

Message emitted:

Assigning result of a function call, where the function returns None

Description:

Used when an assignment is done on a function call but the inferred function returns nothing but None.

Problematic code:

def function():
    return None
f = function()  # [assignment-from-none]

Correct code:

def function():
    return None
f = function() if function() else 1

Created by the typecheck checker.

  await-outside-async / E1142

Message emitted:

'await' should be used within an async function

Description:

Emitted when await is used outside an async function.

Problematic code:

import asyncio
def main():
    await asyncio.sleep(1)  # [await-outside-async]

Correct code:

import asyncio
async def main():
    await asyncio.sleep(1)

Related links:

•   PEP 492

    Created by the typecheck checker.

  bad-configuration-section / E0014

Message emitted:

Out-of-place setting encountered in top level configuration-section '%s' : '%s'

Description:

Used when we detect a setting in the top level of a toml configuration that shouldn't be there.

Additional details:

This error was raised when we encountered an unexpected value type in a toml configuration between pylint 2.12 and pylint 2.14 (before the argparse refactor).

Created by the main checker.

  bad-except-order / E0701

Message emitted:

Bad except clauses order (%s)

Description:

Used when except clauses are not in the correct order (from the more specific to the more generic). If you don't fix the order, some exceptions may not be caught by the most specific handler.

Problematic code:

try:
    print(int(input()))
except Exception:
    raise
except TypeError:  # [bad-except-order]
    # This block cannot be reached since TypeError exception
    # is caught by previous exception handler.
    raise

Correct code:

try:
    print(int(input()))
except TypeError:
    raise
except Exception:
    raise

Created by the exceptions checker.

  bad-exception-cause / E0705

Message emitted:

Exception cause set to something which is not an exception, nor None

Description:

Used when using the syntax "raise ... from ...", where the exception cause is not an exception, nor None.

Problematic code:

def divide(x, y):
    result = 0
    try:
        result = x / y
    except ZeroDivisionError:
        # +1: [bad-exception-cause]
        raise ValueError(f"Division by zero when dividing {x} by {y} !") from result
    return result

Correct code:

def divide(x, y):
    result = 0
    try:
        result = x / y
    except ZeroDivisionError as exc:
        raise ValueError(f"Division by zero when dividing {x} by {y} !") from exc
    return result

Related links:

•   The raise statement

•   Explicit Exception Chaining per PEP 3134

    Created by the exceptions checker.

  bad-format-character / E1300

Message emitted:

Unsupported format character %r (%#02x) at index %d

Description:

Used when an unsupported format character is used in a format string.

Problematic code:

print("%s %z" % ("hello", "world"))  # [bad-format-character]

Correct code:

print("%s %s" % ("hello", "world"))

Additional details:

This check is currently only active for "old-style" string formatting as seen in the examples. See Issue #6085 for more information.

Related links:

•   Format String Syntax

•   PyFormat

    Created by the string checker.

  bad-plugin-value / E0013

Message emitted:

Plugin '%s' is impossible to load, is it installed ? ('%s')

Description:

Used when a bad value is used in 'load-plugins'.

Correct code:

# This is a placeholder for correct code for this message.

Additional details:

You can help us make the doc better by contributing !

Created by the main checker.

  bad-reversed-sequence / E0111

Message emitted:

The first reversed() argument is not a sequence

Description:

Used when the first argument to reversed() builtin isn't a sequence (does not implement __reversed__, nor __getitem__ and __len__

Problematic code:

reversed({1, 2, 3, 4})  # [bad-reversed-sequence]

Correct code:

reversed([1, 2, 3, 4])

Created by the basic checker.

  bad-str-strip-call / E1310

Message emitted:

Suspicious argument in %s.%s call

Description:

The argument to a str.{l,r,}strip call contains a duplicate character,

Problematic code:

"Hello World".strip("Hello")  # [bad-str-strip-call]
# >>> ' World'
"abcbc def bacabc".strip("abcbc ")  # [bad-str-strip-call]
# >>> 'def'

Correct code:

"Hello World".strip("Helo")
# >>> ' World'
"abcbc def bacabc".strip("abc ")
# >>> 'def'

Additional details:

A common misconception is that str.strip('Hello') removes the substring 'Hello' from the beginning and end of the string. This is not the case. From the documentation:

> The chars argument is not a prefix or suffix; rather, all combinations of its values are stripped

Duplicated characters in the str.strip call, besides not having any effect on the actual result, may indicate this misunderstanding.

Related links:

•   Documentation: str.strip([chars])

    Created by the string checker.

  bad-string-format-type / E1307

Message emitted:

Argument %r does not match format type %r

Description:

Used when a type required by format string is not suitable for actual argument type

Problematic code:

print("%d" % "1")  # [bad-string-format-type]

Correct code:

print("%d" % 1)

Additional details:

This check is currently only active for "old-style" string formatting as seen in the examples. See Issue #6085 for more information.

Related links:

•   Format String Syntax

•   PyFormat

    Created by the string checker.

  bad-super-call / E1003

Message emitted:

Bad first argument %r given to super()

Description:

Used when another argument than the current class is given as first argument of the super builtin.

Problematic code:

class Animal:
    pass
class Tree:
    pass
class Cat(Animal):
    def __init__(self):
        super(Tree, self).__init__()  # [bad-super-call]
        super(Animal, self).__init__()

Correct code:

class Animal:
    pass
class Tree:
    pass
class Cat(Animal):
    def __init__(self):
        super(Animal, self).__init__()

Additional details:

In Python 2.7, super() has to be called with its own class and self as arguments (super(Cat, self)), which can lead to a mix up of parent and child class in the code.

In Python 3 the recommended way is to call super() without arguments (see also super-with-arguments).

One exception is calling super() on a non-direct parent class. This can be used to get a method other than the default method returned by the mro().

Related links:

•   Documentation for super()

    Created by the newstyle checker.

  bidirectional-unicode / E2502

Message emitted:

Contains control characters that can permit obfuscated code executed differently than displayed

Description:

bidirectional unicode are typically not displayed characters required to display right-to-left (RTL) script (i.e. Chinese, Japanese, Arabic, Hebrew, ...) correctly. So can you trust this code? Are you sure it displayed correctly in all editors? If you did not write it or your language is not RTL, remove the special characters, as they could be used to trick you into executing code, that does something else than what it looks like. More Information: https://en.wikipedia.org/wiki/Bidirectional_text https://trojansource.codes/

Problematic code:

# +1: [bidirectional-unicode]
example = "x‏" * 100  #    "‏x" is assigned

Correct code:

example = "x[U+2194]" * 100

Created by the unicode_checker checker.

  broken-collections-callable / E6005

Message emitted:

'collections.abc.Callable' inside Optional and Union is broken in 3.9.0 / 3.9.1 (use 'typing.Callable' instead)

Description:

``collections.abc.Callable`` inside Optional and Union is broken in Python 3.9.0 and 3.9.1. Use ``typing.Callable`` for these cases instead. https://bugs.python.org/issue42965

Problematic code:

from collections.abc import Callable
from typing import Optional
def func() -> Optional[Callable[[int], None]]:  # [broken-collections-callable]
    ...

Correct code:

from typing import Callable, Optional
def func() -> Optional[Callable[[int], None]]:
    ...

Configuration file:

[main]
py-version=3.9
load-plugins=pylint.extensions.typing

Related links:

•   bpo-42965

    NOTE:

This message is emitted by the optional 'typing'
    checker which requires the pylint.extensions.typing plugin to be loaded.

    Created by the typing checker.

  broken-noreturn / E6004

Message emitted:

'NoReturn' inside compound types is broken in 3.7.0 / 3.7.1

Description:

``typing.NoReturn`` inside compound types is broken in Python 3.7.0 and 3.7.1. If not dependent on runtime introspection, use string annotation instead. E.g. ``Callable[..., 'NoReturn']``. https://bugs.python.org/issue34921

Problematic code:

from typing import NoReturn, Union
def exploding_apple(apple) -> Union[None, NoReturn]:  # [broken-noreturn]
    print(f"{apple} is about to explode")

Correct code:

from typing import NoReturn
def exploding_apple(apple) -> NoReturn:
    print(f"{apple} is about to explode")
    raise Exception("{apple} exploded !")

Configuration file:

[main]
py-version=3.7
load-plugins=pylint.extensions.typing

NOTE:

This message is emitted by the optional 'typing'
    checker which requires the pylint.extensions.typing plugin to be loaded.

    Created by the typing checker.

  catching-non-exception / E0712

Message emitted:

Catching an exception which doesn't inherit from Exception: %s

Description:

Used when a class which doesn't inherit from Exception is used as an exception in an except clause.

Problematic code:

class FooError:
    pass
try:
    1 / 0
except FooError:  # [catching-non-exception]
    pass

Correct code:

class FooError(Exception):
    pass
try:
    1 / 0
except FooError:
    pass

Created by the exceptions checker.

  class-variable-slots-conflict / E0242

Message emitted:

Value %r in slots conflicts with class variable

Description:

Used when a value in __slots__ conflicts with a class variable, property or method.

Problematic code:

class Person:
    # +1: [class-variable-slots-conflict, class-variable-slots-conflict, class-variable-slots-conflict]
    __slots__ = ("age", "name", "say_hi")
    name = None
    def __init__(self, age, name):
        self.age = age
        self.name = name
    @property
    def age(self):
        return self.age
    def say_hi(self):
        print(f"Hi, I'm {self.name}.")

Correct code:

class Person:
    __slots__ = ("_age", "name",)
    def __init__(self, age, name):
        self._age = age
        self.name = name
    @property
    def age(self):
        return self._age
    def say_hi(self):
        print(f"Hi, I'm {self.name}.")

Created by the classes checker.

  continue-in-finally / E0116

Message emitted:

'continue' not supported inside 'finally' clause

Description:

Emitted when the `continue` keyword is found inside a finally clause, which is a SyntaxError.

Problematic code:

while True:
    try:
        pass
    finally:
        continue  # [continue-in-finally]

Correct code:

while True:
    try:
        pass
    except ValueError:
        pass
    else:
        continue

Configuration file:

[MAIN]
py-version=3.7

Additional details:

Note this message can't be emitted when using Python version 3.8 or greater.

Created by the basic checker.

  dict-iter-missing-items / E1141

Message emitted:

Unpacking a dictionary in iteration without calling .items()

Description:

Emitted when trying to iterate through a dict without calling .items()

Problematic code:

data = {'Paris': 2_165_423, 'New York City': 8_804_190, 'Tokyo': 13_988_129}
for city, population in data:  # [dict-iter-missing-items]
    print(f"{city} has population {population}.")

Correct code:

data = {'Paris': 2_165_423, 'New York City': 8_804_190, 'Tokyo': 13_988_129}
for city, population in data.items():
    print(f"{city} has population {population}.")

Created by the typecheck checker.

  duplicate-argument-name / E0108

Message emitted:

Duplicate argument name %s in function definition

Description:

Duplicate argument names in function definitions are syntax errors.

Problematic code:

def get_fruits(apple, banana, apple):  # [duplicate-argument-name]
    pass

Correct code:

def get_fruits(apple, banana, orange):
    pass

Created by the basic checker.

  duplicate-bases / E0241

Message emitted:

Duplicate bases for class %r

Description:

Duplicate use of base classes in derived classes raise TypeErrors.

Problematic code:

class Animal:
    pass
class Cat(Animal, Animal):  # [duplicate-bases]
    pass

Correct code:

class Animal:
    pass
class Bird(Animal):
    pass
class Cat(Animal):
    pass

Created by the classes checker.

  format-needs-mapping / E1303

Message emitted:

Expected mapping for format string, not %s

Description:

Used when a format string that uses named conversion specifiers is used with an argument that is not a mapping.

Problematic code:

print("%(x)d %(y)d" % [1, 2])  # [format-needs-mapping]

Correct code:

print("%(x)d %(y)d" % {"x": 1, "y": 2})

Created by the string checker.

  function-redefined / E0102

Message emitted:

%s already defined line %s

Description:

Used when a function / class / method is redefined.

Problematic code:

def get_email():
    pass
def get_email():  # [function-redefined]
    pass

Correct code:

def get_email():
    pass

Created by the basic checker.

  inconsistent-mro / E0240

Message emitted:

Inconsistent method resolution order for class %r

Description:

Used when a class has an inconsistent method resolution order.

Problematic code:

class A:
    pass
class B(A):
    pass
class C(A, B):  # [inconsistent-mro]
    pass

Correct code:

class A:
    pass
class B(A):
    pass
class C(B):  # or B, A or A but not A, B
    pass

Created by the classes checker.

  inherit-non-class / E0239

Message emitted:

Inheriting %r, which is not a class.

Description:

Used when a class inherits from something which is not a class.

Problematic code:

class Fruit(bool):  # [inherit-non-class]
    pass

Correct code:

class Fruit:
    def __bool__(self):
        pass

Created by the classes checker.

  init-is-generator / E0100

Message emitted:

__init__ method is a generator

Description:

Used when the special class method __init__ is turned into a generator by a yield in its body.

Problematic code:

class Fruit:
    def __init__(self, worms):  # [init-is-generator]
        yield from worms
apple = Fruit(["Fahad", "Anisha", "Tabatha"])

Correct code:

class Fruit:
    def __init__(self, worms):
        self.__worms = worms
    def worms(self):
        yield from self.__worms
apple = Fruit(["Fahad", "Anisha", "Tabatha"])
for worm in apple.worms():
    pass

Created by the basic checker.

  invalid-all-format / E0605

Message emitted:

Invalid format for __all__, must be tuple or list

Description:

Used when __all__ has an invalid format.

Problematic code:

__all__ = ("CONST")  # [invalid-all-format]
CONST = 42

Correct code:

__all__ = ("CONST",)
CONST = 42

Created by the variables checker.

  invalid-all-object / E0604

Message emitted:

Invalid object %r in __all__, must contain only strings

Description:

Used when an invalid (non-string) object occurs in __all__.

Problematic code:

__all__ = (
    None,  # [invalid-all-object]
    Fruit,
    Worm,
)
class Fruit:
    pass
class Worm:
    pass

Correct code:

__all__ = ['Fruit', 'Worm']
class Fruit:
    pass
class Worm:
    pass

Additional details:

From The Python Language Reference – The import statement:
    "The public names defined by a module are determined by checking the module's namespace for a variable named __all__; if defined, it must be a sequence of strings which are names defined or imported by that module."

    Related links:

•   PEP 8 – Style Guide for Python Code

    Created by the variables checker.

  invalid-bool-returned / E0304

Message emitted:

__bool__ does not return bool

Description:

Used when a __bool__ method returns something which is not a bool

Problematic code:

class BadBool:
    """__bool__ returns an int"""
    def __bool__(self):  # [invalid-bool-returned]
        return 1

Correct code:

class GoodBool:
    """__bool__ returns `bool`"""
    def __bool__(self):
        return True

Created by the classes checker.

  invalid-bytes-returned / E0308

Message emitted:

__bytes__ does not return bytes

Description:

Used when a __bytes__ method returns something which is not bytes

Problematic code:

class BadBytes:
    """__bytes__ returns <type 'str'>"""
    def __bytes__(self):  # [invalid-bytes-returned]
        return "123"

Correct code:

class GoodBytes:
    """__bytes__ returns <type 'bytes'>"""
    def __bytes__(self):
        return b"some bytes"

Created by the classes checker.

  invalid-character-backspace / E2510

Message emitted:

Invalid unescaped character backspace, use "\b" instead.

Description:

Moves the cursor back, so the character after it will overwrite the character before.

Problematic code:

STRING = "Invalid character backspace " # [invalid-character-backspace]

Correct code:

STRING = "Valid character backspace \b"

Created by the unicode_checker checker.

  invalid-character-carriage-return / E2511

Message emitted:

Invalid unescaped character carriage-return, use "\r" instead.

Description:

Moves the cursor to the start of line, subsequent characters overwrite the start of the line.

Correct code:

# This is a placeholder for correct code for this message.

Additional details:

You can help us make the doc better by contributing !

Created by the unicode_checker checker.

  invalid-character-esc / E2513

Message emitted:

Invalid unescaped character esc, use "\x1B" instead.

Description:

Commonly initiates escape codes which allow arbitrary control of the terminal.

Problematic code:

STRING = "Invalid escape character " # [invalid-character-esc]

Correct code:

STRING = "Valid escape character \x1B"

Created by the unicode_checker checker.

  invalid-character-nul / E2514

Message emitted:

Invalid unescaped character nul, use "\0" instead.

Description:

Mostly end of input for python.

Correct code:

# This is a placeholder for correct code for this message.

Additional details:

You can help us make the doc better by contributing !

Created by the unicode_checker checker.

  invalid-character-sub / E2512

Message emitted:

Invalid unescaped character sub, use "\x1A" instead.

Description:

Ctrl+Z "End of text" on Windows. Some programs (such as type) ignore the rest of the file after it.

Problematic code:

STRING = "Invalid character sub " # [invalid-character-sub]

Correct code:

STRING = "Valid character sub x1A"

Created by the unicode_checker checker.

  invalid-character-zero-width-space / E2515

Message emitted:

Invalid unescaped character zero-width-space, use "\u200B" instead.

Description:

Invisible space character could hide real code execution.

Problematic code:

STRING = "Invalid character zero-width-space ​" # [invalid-character-zero-width-space]

Correct code:

STRING = "Valid character zero-width-space u200B"

Created by the unicode_checker checker.

  invalid-class-object / E0243

Message emitted:

Invalid assignment to '__class__'. Should be a class definition but got a '%s'

Description:

Used when an invalid object is assigned to a __class__ property. Only a class is permitted.

Problematic code:

class Apple:
    pass
Apple.__class__ = 1  # [invalid-class-object]

Correct code:

class Apple:
    pass
class RedDelicious:
    pass
Apple.__class__ = RedDelicious

Created by the classes checker.

  invalid-enum-extension / E0244

Message emitted:

Extending inherited Enum class "%s"

Description:

Used when a class tries to extend an inherited Enum class. Doing so will raise a TypeError at runtime.

Problematic code:

from enum import Enum
class Color(Enum):
    ORANGE = 1
    CHERRY = 2
class Fruit(Color):  # [invalid-enum-extension]
    APPLE = 3

Correct code:

from enum import Enum
class Color(Enum):
    ORANGE = 1
    CHERRY = 2
class Fruit(Enum):
    ORANGE = 1
    CHERRY = 2
    APPLE = 3

Created by the classes checker.

  invalid-envvar-value / E1507

Message emitted:

%s does not support %s type argument

Description:

Env manipulation functions support only string type arguments. See https://docs.python.org/3/library/os.html#os.getenv.

Problematic code:

import os
os.getenv(1)  # [invalid-envvar-value]

Correct code:

import os
os.getenv('1')

Created by the stdlib checker.

  invalid-format-returned / E0311

Message emitted:

__format__ does not return str

Description:

Used when a __format__ method returns something which is not a string

Problematic code:

class BadFormat:
    """__format__ returns <type 'int'>"""
    def __format__(self, format_spec):  # [invalid-format-returned]
        return 1

Correct code:

class GoodFormat:
    """__format__ returns <type 'str'>"""
    def __format__(self, format_spec):
        return "hello!"

Created by the classes checker.

  invalid-getnewargs-ex-returned / E0313

Message emitted:

__getnewargs_ex__ does not return a tuple containing (tuple, dict)

Description:

Used when a __getnewargs_ex__ method returns something which is not of the form tuple(tuple, dict)

Problematic code:

class BadGetNewArgsEx:
    """__getnewargs_ex__ returns tuple with incorrect arg length"""
    def __getnewargs_ex__(self):  # [invalid-getnewargs-ex-returned]
        return (tuple(1), dict(x="y"), 1)

Correct code:

class GoodGetNewArgsEx:
    """__getnewargs_ex__ returns <type 'tuple'>"""
    def __getnewargs_ex__(self):
        return ((1,), {"2": 2})

Created by the classes checker.

  invalid-getnewargs-returned / E0312

Message emitted:

__getnewargs__ does not return a tuple

Description:

Used when a __getnewargs__ method returns something which is not a tuple

Problematic code:

class BadGetNewArgs:
    """__getnewargs__ returns an integer"""
    def __getnewargs__(self):  # [invalid-getnewargs-returned]
        return 1

Correct code:

class GoodGetNewArgs:
    """__getnewargs__ returns <type 'tuple'>"""
    def __getnewargs__(self):
        return (1, 2)

Created by the classes checker.

  invalid-hash-returned / E0309

Message emitted:

__hash__ does not return int

Description:

Used when a __hash__ method returns something which is not an integer

Problematic code:

class BadHash:
    """__hash__ returns dict"""
    def __hash__(self):  # [invalid-hash-returned]
        return {}

Correct code:

class GoodHash:
    """__hash__ returns `int`"""
    def __hash__(self):
        return 19

Created by the classes checker.

  invalid-index-returned / E0305

Message emitted:

__index__ does not return int

Description:

Used when an __index__ method returns something which is not an integer

Problematic code:

class BadIndex:
    """__index__ returns a dict"""
    def __index__(self):  # [invalid-index-returned]
        return {"19": "19"}

Correct code:

class GoodIndex:
    """__index__ returns <type 'int'>"""
    def __index__(self):
        return 19

Created by the classes checker.

  invalid-length-hint-returned / E0310

Message emitted:

__length_hint__ does not return non-negative integer

Description:

Used when a __length_hint__ method returns something which is not a non-negative integer

Problematic code:

class BadLengthHint:
    """__length_hint__ returns non-int"""
    def __length_hint__(self):  # [invalid-length-hint-returned]
        return 3.0

Correct code:

class GoodLengthHint:
    """__length_hint__ returns <type 'int'>"""
    def __length_hint__(self):
        return 10

Created by the classes checker.

  invalid-length-returned / E0303

Message emitted:

__len__ does not return non-negative integer

Description:

Used when a __len__ method returns something which is not a non-negative integer

Problematic code:

class FruitBasket:
    def __init__(self, fruits):
        self.fruits = ["Apple", "Banana", "Orange"]
    def __len__(self):  # [invalid-length-returned]
        return - len(self.fruits)

Correct code:

class FruitBasket:
    def __init__(self, fruits):
        self.fruits = ["Apple", "Banana", "Orange"]
    def __len__(self):
        return len(self.fruits)

Created by the classes checker.

  invalid-metaclass / E1139

Message emitted:

Invalid metaclass %r used

Description:

Emitted whenever we can detect that a class is using, as a metaclass, something which might be invalid for using as a metaclass.

Problematic code:

class Apple(metaclass=int):  # [invalid-metaclass]
    pass

Correct code:

class Plant:
    pass
class Apple(Plant):
    pass

Created by the typecheck checker.

  invalid-repr-returned / E0306

Message emitted:

__repr__ does not return str

Description:

Used when a __repr__ method returns something which is not a string

Problematic code:

class Repr:
    """__repr__ returns <type 'int'>"""
    def __repr__(self):  # [invalid-repr-returned]
        return 1

Correct code:

class Repr:
    """__repr__ returns <type 'str'>"""
    def __repr__(self):
        return "apples"

Created by the classes checker.

  invalid-sequence-index / E1126

Message emitted:

Sequence index is not an int, slice, or instance with __index__

Description:

Used when a sequence type is indexed with an invalid type. Valid types are ints, slices, and objects with an __index__ method.

Problematic code:

fruits = ['apple', 'banana', 'orange']
print(fruits['apple'])  # [invalid-sequence-index]

Correct code:

fruits = ['apple', 'banana', 'orange']
print(fruits[0])

Additional details:

Be careful with [True] or [False] as sequence index, since True and False will respectively be evaluated as 1 and 0 and will bring the second element of the list and the first without erroring.

Created by the typecheck checker.

  invalid-slice-index / E1127

Message emitted:

Slice index is not an int, None, or instance with __index__

Description:

Used when a slice index is not an integer, None, or an object with an __index__ method.

Problematic code:

LETTERS = ["a", "b", "c", "d"]
FIRST_THREE = LETTERS[:"3"]  # [invalid-slice-index]

Correct code:

LETTERS = ["a", "b", "c", "d"]
FIRST_THREE = LETTERS[:3]

Created by the typecheck checker.

  invalid-slice-step / E1144

Message emitted:

Slice step cannot be 0

Description:

Used when a slice step is 0 and the object doesn't implement a custom __getitem__ method.

Problematic code:

LETTERS = ["a", "b", "c", "d"]
LETTERS[::0]  # [invalid-slice-step]

Correct code:

LETTERS = ["a", "b", "c", "d"]
LETTERS[::2]

Created by the typecheck checker.

  invalid-slots / E0238

Message emitted:

Invalid __slots__ object

Description:

Used when an invalid __slots__ is found in class. Only a string, an iterable or a sequence is permitted.

Problematic code:

class Person:  # [invalid-slots]
    __slots__ = 42

Correct code:

class Person:
    __slots__ = ("name", "age",)

Created by the classes checker.

  invalid-slots-object / E0236

Message emitted:

Invalid object %r in __slots__, must contain only non empty strings

Description:

Used when an invalid (non-string) object occurs in __slots__.

Problematic code:

class Person:
    __slots__ = ('name', 3)  # [invalid-slots-object]

Correct code:

class Person:
    __slots__ = ('name', 'surname')

Related links:

•   Documentation for __slots__

    Created by the classes checker.

  invalid-star-assignment-target / E0113

Message emitted:

Starred assignment target must be in a list or tuple

Description:

Emitted when a star expression is used as a starred assignment target.

Problematic code:

*fruit = ['apple', 'banana', 'orange']  # [invalid-star-assignment-target]

Correct code:

fruit = ['apple', 'banana', 'orange']

Created by the basic checker.

  invalid-str-returned / E0307

Message emitted:

__str__ does not return str

Description:

Used when a __str__ method returns something which is not a string

Problematic code:

class Str:
    """__str__ returns int"""
    def __str__(self):  # [invalid-str-returned]
        return 1

Correct code:

class Str:
    """__str__ returns <type 'str'>"""
    def __str__(self):
        return "oranges"

Created by the classes checker.

  invalid-unary-operand-type / E1130

Message emitted:

%s

Description:

Emitted when a unary operand is used on an object which does not support this type of operation.

Problematic code:

cherries = 10
eaten_cherries = int
cherries = - eaten_cherries  # [invalid-unary-operand-type]

Correct code:

cherries = 10
eaten_cherries = 2
cherries -= eaten_cherries

Created by the typecheck checker.

  invalid-unicode-codec / E2501

Message emitted:

UTF-16 and UTF-32 aren't backward compatible. Use UTF-8 instead

Description:

For compatibility use UTF-8 instead of UTF-16/UTF-32. See also https://bugs.python.org/issue1503789 for a history of this issue. And https://softwareengineering.stackexchange.com/questions/102205/ for some possible problems when using UTF-16 for instance.

Correct code:

# This is a placeholder for correct code for this message.

Additional details:

You can help us make the doc better by contributing !

Created by the unicode_checker checker.

  logging-format-truncated / E1201

Message emitted:

Logging format string ends in middle of conversion specifier

Description:

Used when a logging statement format string terminates before the end of a conversion specifier.

Problematic code:

import logging
logging.warning("Here is a variable: %", my_var)  # [logging-format-truncated]

Correct code:

import logging
logging.warning("Here is a variable: %s", my_var)

Created by the logging checker.

  logging-too-few-args / E1206

Message emitted:

Not enough arguments for logging format string

Description:

Used when a logging format string is given too few arguments.

Problematic code:

import logging
try:
    function()
except Exception as e:
    logging.error('%s error occurred: %s', e)  # [logging-too-few-args]
    raise

Correct code:

import logging
try:
    function()
except Exception as e:
    logging.error('%s error occurred: %s', type(e), e)
    raise

Created by the logging checker.

  logging-too-many-args / E1205

Message emitted:

Too many arguments for logging format string

Description:

Used when a logging format string is given too many arguments.

Problematic code:

import logging
try:
    function()
except Exception as e:
    logging.error('Error occurred: %s', type(e), e)  # [logging-too-many-args]
    raise

Correct code:

import logging
try:
    function()
except Exception as e:
    logging.error('%s error occurred: %s', type(e), e)
    raise

Created by the logging checker.

  logging-unsupported-format / E1200

Message emitted:

Unsupported logging format character %r (%#02x) at index %d

Description:

Used when an unsupported format character is used in a logging statement format string.

Problematic code:

import logging
logging.info("%s %y !", "Hello", "World") # [logging-unsupported-format]

Correct code:

import logging
logging.info("%s %s !", "Hello", "World")

Created by the logging checker.

  method-hidden / E0202

Message emitted:

An attribute defined in %s line %s hides this method

Description:

Used when a class defines a method which is hidden by an instance attribute from an ancestor class or set by some client code.

Problematic code:

class Fruit:
    def __init__(self, vitamins):
        self.vitamins = vitamins
    def vitamins(self):  # [method-hidden]
        pass

Correct code:

class Fruit:
    def __init__(self, vitamins):
        self.vitamins = vitamins
    def antioxidants(self):
        pass

Created by the classes checker.

  misplaced-bare-raise / E0704

Message emitted:

The raise statement is not inside an except clause

Description:

Used when a bare raise is not used inside an except clause. This generates an error, since there are no active exceptions to be reraised. An exception to this rule is represented by a bare raise inside a finally clause, which might work, as long as an exception is raised inside the try block, but it is nevertheless a code smell that must not be relied upon.

Problematic code:

def validate_positive(x):
    if x <= 0:
        raise  # [misplaced-bare-raise]

Correct code:

def validate_positive(x):
    if x <= 0:
        raise ValueError(f"{x} is not positive")

Created by the exceptions checker.

  misplaced-format-function / E0119

Message emitted:

format function is not called on str

Description:

Emitted when format function is not called on str object. e.g doing print("value: {}").format(123) instead of print("value: {}".format(123)). This might not be what the user intended to do.

Problematic code:

print('Value: {}').format('Car')  # [misplaced-format-function]

Correct code:

print('Value: {}'.format('Car'))

Created by the basic checker.

  missing-format-string-key / E1304

Message emitted:

Missing key %r in format string dictionary

Description:

Used when a format string that uses named conversion specifiers is used with a dictionary that doesn't contain all the keys required by the format string.

Problematic code:

# +1: [missing-format-string-key]
fruit_prices = """
Apple: %(apple_price)d ¤
Orange: %(orange_price)d ¤
""" % {
    "apple_price": 42
}

Correct code:

fruit_prices = """
Apple: %(apple_price)d ¤
Orange: %(orange_price)d ¤
""" % {
    "apple_price": 42,
    "orange_price": 87,
}

Created by the string checker.

  missing-kwoa / E1125

Message emitted:

Missing mandatory keyword argument %r in %s call

Description:

Used when a function call does not pass a mandatory keyword-only argument.

Problematic code:

def target(pos, *, keyword):
    return pos + keyword
def not_forwarding_kwargs(*args, **kwargs):
    target(*args) # [missing-kwoa]

Correct code:

def target(pos, *, keyword):
    return pos + keyword
def not_forwarding_kwargs(*args, **kwargs):
    target(*args, **kwargs)

Created by the typecheck checker.

  mixed-format-string / E1302

Message emitted:

Mixing named and unnamed conversion specifiers in format string

Description:

Used when a format string contains both named (e.g. '%(foo)d') and unnamed (e.g. '%d') conversion specifiers. This is also used when a named conversion specifier contains * for the minimum field width and/or precision.

Problematic code:

print("x=%(x)d, y=%d" % (0, 1))  # [mixed-format-string]

Correct code:

print("x=%d, y=%d" % (0, 1))
print("x=%(x)d, y=%(y)d" % {"x": 0, "y": 1})

Created by the string checker.

  modified-iterating-dict / E4702

Message emitted:

Iterated dict '%s' is being modified inside for loop body, iterate through a copy of it instead.

Description:

Emitted when items are added or removed to a dict being iterated through. Doing so raises a RuntimeError.

Problematic code:

fruits = {"apple": 1, "orange": 2, "mango": 3}
i = 0
for fruit in fruits:
    fruits["apple"] = i  # [modified-iterating-dict]
    i += 1

Correct code:

fruits = {"apple": 1, "orange": 2, "mango": 3}
i = 0
for fruit in fruits.copy():
    fruits["apple"] = i
    i += 1

Created by the modified_iteration checker.

  modified-iterating-set / E4703

Message emitted:

Iterated set '%s' is being modified inside for loop body, iterate through a copy of it instead.

Description:

Emitted when items are added or removed to a set being iterated through. Doing so raises a RuntimeError.

Problematic code:

fruits = {"apple", "orange", "mango"}
for fruit in fruits:
    fruits.add(fruit + "yum")  # [modified-iterating-set]

Correct code:

fruits = {"apple", "orange", "mango"}
for fruit in fruits.copy():
    fruits.add(fruit + "yum")

Created by the modified_iteration checker.

  no-member / E1101

Message emitted:

%s %r has no %r member%s

Description:

Used when a variable is accessed for a nonexistent member.

Problematic code:

from pathlib import Path
directories = Path(".").mothers  # [no-member]
class Cat:
    def meow(self):
        print("Meow")
Cat().roar()  # [no-member]

Correct code:

from pathlib import Path
directories = Path(".").parents
class Cat:
    def meow(self):
        print("Meow")
Cat().meow()

Additional details:

If you are getting the dreaded no-member error, there is a possibility that either:

•   pylint found a bug in your code

•   You're launching pylint without the dependencies installed in its environment

•   pylint would need to lint a C extension module and is refraining to do so

•   pylint does not understand dynamically generated code

    Linting C extension modules is not supported out of the box, especially since pylint has no way to get an AST object out of the extension module.

    But pylint actually has a mechanism which you might use in case you want to analyze C extensions. Pylint has a flag, called extension-pkg-allow-list (formerly extension-pkg-whitelist), through which you can tell it to import that module and to build an AST from that imported module:

    $ pylint --extension-pkg-allow-list=your_c_extension

    Be aware though that using this flag means that extensions are loaded into the active Python interpreter and may run arbitrary code, which you may not want. This is the reason why we disable by default loading C extensions. In case you do not want the hassle of passing C extensions module with this flag all the time, you can enable unsafe-load-any-extension in your configuration file, which will build AST objects from all the C extensions that pylint encounters:

    $ pylint --unsafe-load-any-extension=y

    Alternatively, since pylint emits a separate error for attributes that cannot be found in C extensions, c-extension-no-member, you can disable this error for your project.

    If something is generated dynamically, pylint won't be able to understand the code from your library (c-extension or not). You can then specify generated attributes with the generated-members option. For example if cv2.LINE_AA and sphinx.generated_member create false positives for no-member, you can do:

    $ pylint --generated-member=cv2.LINE_AA,sphinx.generated_member

    Created by the typecheck checker.

  no-method-argument / E0211

Message emitted:

Method %r has no argument

Description:

Used when a method which should have the bound instance as first argument has no argument defined.

Problematic code:

class Person:
    def print_greeting():  # [no-method-argument]
        print("hello")

Correct code:

class Person:
    def print_greeting(self):
        print("hello")

Created by the classes checker.

  no-name-in-module / E0611

Message emitted:

No name %r in module %r

Description:

Used when a name cannot be found in a module.

Problematic code:

from os import pizza  # [no-name-in-module]

Correct code:

from os import path

Created by the variables checker.

  no-self-argument / E0213

Message emitted:

Method %r should have "self" as first argument

Description:

Used when a method has an attribute different the "self" as first argument. This is considered as an error since this is a so common convention that you shouldn't break it!

Problematic code:

class Fruit:
    def __init__(this, name):  # [no-self-argument]
        this.name = name

Correct code:

class Fruit:
    def __init__(self, name):
        self.name = name

Created by the classes checker.

  no-value-for-parameter / E1120

Message emitted:

No value for argument %s in %s call

Description:

Used when a function call passes too few arguments.

Problematic code:

def add(x, y):
    return x + y
add(1)  # [no-value-for-parameter]

Correct code:

def add(x, y):
    return x + y
add(1, 2)

Created by the typecheck checker.

  non-iterator-returned / E0301

Message emitted:

__iter__ returns non-iterator

Description:

Used when an __iter__ method returns something which is not an iterable (i.e. has no `__next__` method)

Problematic code:

import random
class GenericAstrology:
    def __init__(self, signs, predictions):
        self.signs = signs
        self.predictions = predictions
    def __iter__(self):  # [non-iterator-returned]
        self.index = 0
        self.number_of_prediction = len(self.predictions)
        return self
SIGNS = ["Aries", "Taurus", "Gemini", "Cancer", "Leo", "Virgo", "Libra"]
PREDICTIONS = ["good things", "bad thing", "existential dread"]
for sign, prediction in GenericAstrology(SIGNS, PREDICTIONS):
    print(f"{sign} : {prediction} today")

Correct code:

import random
class GenericAstrology:
    def __init__(self, signs, predictions):
        self.signs = signs
        self.predictions = predictions
    def __iter__(self):
        self.index = 0
        self.number_of_prediction = len(self.predictions)
        return self
    def __next__(self):
        if self.index == len(self.signs):
            raise StopIteration
        self.index += 1
        prediction_index = random.randint(0, self.number_of_prediction - 1)
        return self.signs[self.index - 1], self.predictions[prediction_index]
SIGNS = ["Aries", "Taurus", "Gemini", "Cancer", "Leo", "Virgo", "Libra"]
PREDICTIONS = ["good things", "bad thing", "existential dread"]
for sign, prediction in GenericAstrology(SIGNS, PREDICTIONS):
    print(f"{sign} : {prediction} today")

Created by the classes checker.

  nonexistent-operator / E0107

Message emitted:

Use of the non-existent %s operator

Description:

Used when you attempt to use the C-style pre-increment or pre-decrement operator -- and ++, which doesn't exist in Python.

Problematic code:

i = 0
while i <= 10:
    print(i)
    ++i  # [nonexistent-operator]

Correct code:

i = 0
while i <= 10:
    print(i)
    i += 1

Created by the basic checker.

  nonlocal-and-global / E0115

Message emitted:

Name %r is nonlocal and global

Description:

Emitted when a name is both nonlocal and global.

Problematic code:

NUMBER = 42
def update_number(number):  # [nonlocal-and-global]
    global NUMBER
    nonlocal NUMBER
    NUMBER = number
    print(f"New global number is: {NUMBER}")
update_number(24)

Correct code:

NUMBER = 42
def update_number(number):
    global NUMBER
    NUMBER = number
    print(f"New global number is: {NUMBER}")
update_number(24)

Created by the basic checker.

  nonlocal-without-binding / E0117

Message emitted:

nonlocal name %s found without binding

Description:

Emitted when a nonlocal variable does not have an attached name somewhere in the parent scopes

Problematic code:

class Fruit:
    def get_color(self):
        nonlocal colors  # [nonlocal-without-binding]

Correct code:

class Fruit:
    colors = ["red", "green"]
    def get_color(self):
        nonlocal colors

Created by the basic checker.

  not-a-mapping / E1134

Message emitted:

Non-mapping value %s is used in a mapping context

Description:

Used when a non-mapping value is used in place where mapping is expected

Problematic code:

def print_colors(**colors):
    print(colors)
print_colors(**list("red", "black"))  # [not-a-mapping]

Correct code:

def print_colors(**colors):
    print(colors)
print_colors(**dict(red=1, black=2))

Created by the typecheck checker.

  not-an-iterable / E1133

Message emitted:

Non-iterable value %s is used in an iterating context

Description:

Used when a non-iterable value is used in place where iterable is expected

Problematic code:

for i in 10:  # [not-an-iterable]
    pass

Correct code:

for i in "10":
    pass

Created by the typecheck checker.

  not-async-context-manager / E1701

Message emitted:

Async context manager '%s' doesn't implement __aenter__ and __aexit__.

Description:

Used when an async context manager is used with an object that does not implement the async context management protocol.

Problematic code:

class ContextManager:
    def __enter__(self):
        pass
    def __exit__(self, *exc):
        pass
async def foo():
    async with ContextManager():  # [not-async-context-manager]
        pass

Correct code:

class AsyncContextManager:
    def __aenter__(self):
        pass
    def __aexit__(self, *exc):
        pass
async def foo():
    async with AsyncContextManager():
        pass

Additional details:

Async context manager doesn't implement __aenter__ and __aexit__. It can't be emitted when using Python < 3.5.

Created by the async checker.

  not-callable / E1102

Message emitted:

%s is not callable

Description:

Used when an object being called has been inferred to a non callable object.

Problematic code:

NUMBER = 42
print(NUMBER())  # [not-callable]

Correct code:

NUMBER = 42
print(NUMBER)

Created by the typecheck checker.

  not-context-manager / E1129

Message emitted:

Context manager '%s' doesn't implement __enter__ and __exit__.

Description:

Used when an instance in a with statement doesn't implement the context manager protocol(__enter__/__exit__).

Problematic code:

class MyContextManager:
    def __enter__(self):
        pass
with MyContextManager() as c:  # [not-context-manager]
    pass

Correct code:

class MyContextManager:
    def __enter__(self):
        pass
    def __exit__(self, *exc):
        pass
with MyContextManager() as c:
    pass

Created by the typecheck checker.

  not-in-loop / E0103

Message emitted:

%r not properly in loop

Description:

Used when break or continue keywords are used outside a loop.

Problematic code:

def print_even_numbers():
    for i in range(100):
        if i % 2 == 0:
            print(i)
    else:
        continue  # [not-in-loop]

Correct code:

def print_even_numbers():
    for i in range(100):
        if i % 2:
            continue
        print(i)

Created by the basic checker.

  notimplemented-raised / E0711

Message emitted:

NotImplemented raised - should raise NotImplementedError

Description:

Used when NotImplemented is raised instead of NotImplementedError

Problematic code:

class Worm:
    def bore(self):
        raise NotImplemented  # [notimplemented-raised]

Correct code:

class Worm:
    def bore(self):
        raise NotImplementedError

Created by the exceptions checker.

  positional-only-arguments-expected / E3102

Message emitted:

`%s()` got some positional-only arguments passed as keyword arguments: %s

Description:

Emitted when positional-only arguments have been passed as keyword arguments. Remove the keywords for the affected arguments in the function call.

Problematic code:

def cube(n, /):
    """Takes in a number n, returns the cube of n"""
    return n**3
cube(n=2) # [positional-only-arguments-expected]

Correct code:

def cube(n, /):
    """Takes in a number n, returns the cube of n"""
    return n**3
cube(2)

Related links:

•   PEP 570

    Created by the method_args checker.

  potential-index-error / E0643

Message emitted:

Invalid index for iterable length

Description:

Emitted when an index used on an iterable goes beyond the length of that iterable.

Problematic code:

print([1, 2, 3][3])  # [potential-index-error]

Correct code:

print([1, 2, 3][2])

Created by the variables checker.

  raising-bad-type / E0702

Message emitted:

Raising %s while only classes or instances are allowed

Description:

Used when something which is neither a class nor an instance is raised (i.e. a `TypeError` will be raised).

Problematic code:

class FasterThanTheSpeedOfLightError(ZeroDivisionError):
    def __init__(self):
        super().__init__("You can't go faster than the speed of light !")
def calculate_speed(distance: float, time: float) -> float:
    try:
        return distance / time
    except ZeroDivisionError as e:
        raise None  # [raising-bad-type]

Correct code:

class FasterThanTheSpeedOfLightError(ZeroDivisionError):
    def __init__(self):
        super().__init__("You can't go faster than the speed of light !")
def calculate_speed(distance: float, time: float) -> float:
    try:
        return distance / time
    except ZeroDivisionError as e:
        raise FasterThanTheSpeedOfLightError() from e

Created by the exceptions checker.

  raising-non-exception / E0710

Message emitted:

Raising a new style class which doesn't inherit from BaseException

Description:

Used when a new style class which doesn't inherit from BaseException is raised.

Problematic code:

raise str  # [raising-non-exception]

Correct code:

raise Exception("Goodbye world !")

Created by the exceptions checker.

  redundant-keyword-arg / E1124

Message emitted:

Argument %r passed by position and keyword in %s call

Description:

Used when a function call would result in assigning multiple values to a function parameter, one value from a positional argument and one from a keyword argument.

Problematic code:

def square(x):
    return x * x
square(5, x=4)  # [redundant-keyword-arg]

Correct code:

def square(x):
    return x * x
square(x=4)
# or
square(5)

Created by the typecheck checker.

  relative-beyond-top-level / E0402

Message emitted:

Attempted relative import beyond top-level package

Description:

Used when a relative import tries to access too many levels in the current package.

Correct code:

# This is a placeholder for correct code for this message.

Additional details:

You can help us make the doc better by contributing !

Created by the imports checker.

  repeated-keyword / E1132

Message emitted:

Got multiple values for keyword argument %r in function call

Description:

Emitted when a function call got multiple values for a keyword.

Problematic code:

def func(a, b, c):
    return a, b, c
func(1, 2, c=3, **{"c": 4})  # [repeated-keyword]
func(1, 2, **{"c": 3}, **{"c": 4})  # [repeated-keyword]

Correct code:

def func(a, b, c):
    return a, b, c
func(1, 2, c=3)

Created by the typecheck checker.

  return-arg-in-generator / E0106

Message emitted:

Return with argument inside generator

Description:

Used when a "return" statement with an argument is found outside in a generator function or method (e.g. with some "yield" statements).

Correct code:

# This is a placeholder for correct code for this message.

Additional details:

You can help us make the doc better by contributing !

Created by the basic checker.

  return-in-init / E0101

Message emitted:

Explicit return in __init__

Description:

Used when the special class method __init__ has an explicit return value.

Problematic code:

class Sum:
    def __init__(self, a, b):  # [return-in-init]
        return a + b

Correct code:

class Sum:
    def __init__(self, a, b) -> None:
        self.result = a + b

Related links:

•   __init__ method documentation

    Created by the basic checker.

  return-outside-function / E0104

Message emitted:

Return outside function

Description:

Used when a "return" statement is found outside a function or method.

Problematic code:

return 42  # [return-outside-function]

Correct code:

def get_the_answer():
    return 42

Created by the basic checker.

  singledispatch-method / E1519

Message emitted:

singledispatch decorator should not be used with methods, use singledispatchmethod instead.

Description:

singledispatch should decorate functions and not class/instance methods. Use singledispatchmethod for those cases.

Problematic code:

from functools import singledispatch
class Board:
    @singledispatch  # [singledispatch-method]
    @classmethod
    def convert_position(cls, position):
        pass
    @convert_position.register  # [singledispatch-method]
    @classmethod
    def _(cls, position: str) -> tuple:
        position_a, position_b = position.split(",")
        return (int(position_a), int(position_b))
    @convert_position.register  # [singledispatch-method]
    @classmethod
    def _(cls, position: tuple) -> str:
        return f"{position[0]},{position[1]}"

Correct code:

from functools import singledispatch
class Board:
    @singledispatch
    @staticmethod
    def convert_position(position):
        pass
    @convert_position.register
    @staticmethod
    def _(position: str) -> tuple:
        position_a, position_b = position.split(",")
        return (int(position_a), int(position_b))
    @convert_position.register
    @staticmethod
    def _(position: tuple) -> str:
        return f"{position[0]},{position[1]}"

Created by the stdlib checker.

  singledispatchmethod-function / E1520

Message emitted:

singledispatchmethod decorator should not be used with functions, use singledispatch instead.

Description:

singledispatchmethod should decorate class/instance methods and not functions. Use singledispatch for those cases.

Problematic code:

from functools import singledispatchmethod
class Board:
    @singledispatchmethod  # [singledispatchmethod-function]
    @staticmethod
    def convert_position(position):
        pass
    @convert_position.register  # [singledispatchmethod-function]
    @staticmethod
    def _(position: str) -> tuple:
        position_a, position_b = position.split(",")
        return (int(position_a), int(position_b))
    @convert_position.register  # [singledispatchmethod-function]
    @staticmethod
    def _(position: tuple) -> str:
        return f"{position[0]},{position[1]}"

Correct code:

from functools import singledispatchmethod
class Board:
    @singledispatchmethod
    def convert_position(cls, position):
        pass
    @singledispatchmethod
    @classmethod
    def _(cls, position: str) -> tuple:
        position_a, position_b = position.split(",")
        return (int(position_a), int(position_b))
    @singledispatchmethod
    @classmethod
    def _(cls, position: tuple) -> str:
        return f"{position[0]},{position[1]}"

Created by the stdlib checker.

  star-needs-assignment-target / E0114

Message emitted:

Can use starred expression only in assignment target

Description:

Emitted when a star expression is not used in an assignment target.

Problematic code:

stars = *["Sirius", "Arcturus", "Vega"]  # [star-needs-assignment-target]

Correct code:

sirius, *arcturus_and_vega = ["Sirius", "Arcturus", "Vega"]

Created by the basic checker.

  syntax-error / E0001

Message emitted:

%s

Description:

Used when a syntax error is raised for a module.

Problematic code:

fruit_stock = {
    'apple': 42,
    'orange': 21  # [syntax-error]
    'banana': 12
}

Correct code:

fruit_stock = {
    'apple': 42,
    'orange': 21,
    'banana': 12
}

Created by the main checker.

  too-few-format-args / E1306

Message emitted:

Not enough arguments for format string

Description:

Used when a format string that uses unnamed conversion specifiers is given too few arguments

Problematic code:

print("Today is {0}, so tomorrow will be {1}".format("Monday"))  # [too-few-format-args]

Correct code:

print("Today is {0}, so tomorrow will be {1}".format("Monday", "Tuesday"))

Related links:

•   String Formmating

    Created by the string checker.

  too-many-format-args / E1305

Message emitted:

Too many arguments for format string

Description:

Used when a format string that uses unnamed conversion specifiers is given too many arguments.

Problematic code:

# +1: [too-many-format-args]
print("Today is {0}, so tomorrow will be {1}".format("Monday", "Tuesday", "Wednesday"))

Correct code:

print("Today is {0}, so tomorrow will be {1}".format("Monday", "Tuesday"))

Related links:

•   String Formmating

    Created by the string checker.

  too-many-function-args / E1121

Message emitted:

Too many positional arguments for %s call

Description:

Used when a function call passes too many positional arguments.

Problematic code:

class Fruit:
    def __init__(self, color):
        self.color = color
apple = Fruit("red", "apple", [1, 2, 3])  # [too-many-function-args]

Correct code:

class Fruit:
    def __init__(self, color, name):
        self.color = color
        self.name = name
apple = Fruit("red", "apple")

Created by the typecheck checker.

  too-many-star-expressions / E0112

Message emitted:

More than one starred expression in assignment

Description:

Emitted when there are more than one starred expressions (`*x`) in an assignment. This is a SyntaxError.

Problematic code:

*stars, *constellations = ["Sirius", "Arcturus", "Vega"]  # [too-many-star-expressions]

Correct code:

*sirius_and_arcturus, vega = ["Sirius", "Arcturus", "Vega"]

Created by the basic checker.

  truncated-format-string / E1301

Message emitted:

Format string ends in middle of conversion specifier

Description:

Used when a format string terminates before the end of a conversion specifier.

Problematic code:

PARG_2 = 1
print("strange format %2" % PARG_2) # [truncated-format-string]

Correct code:

PARG_2 = 1
print(f"strange format {PARG_2}")

Created by the string checker.

  undefined-all-variable / E0603

Message emitted:

Undefined variable name %r in __all__

Description:

Used when an undefined variable name is referenced in __all__.

Problematic code:

__all__ = ["get_fruit_colour"]  # [undefined-all-variable]
def get_fruit_color():
    pass

Correct code:

__all__ = ["get_fruit_color"]
def get_fruit_color():
    pass

Related links:

•   Importing * From a Package

    Created by the variables checker.

  undefined-variable / E0602

Message emitted:

Undefined variable %r

Description:

Used when an undefined variable is accessed.

Problematic code:

print(number + 2)  # [undefined-variable]

Correct code:

number = 3
print(number + 2)

Created by the variables checker.

  unexpected-keyword-arg / E1123

Message emitted:

Unexpected keyword argument %r in %s call

Description:

Used when a function call passes a keyword argument that doesn't correspond to one of the function's parameter names.

Problematic code:

def print_coordinates(x=0, y=0):
    print(f"{x=}, {y=}")
print_coordinates(x=1, y=2, z=3)  # [unexpected-keyword-arg]

Correct code:

def print_coordinates(x=0, y=0):
    print(f"{x=}, {y=}")
print_coordinates(x=1, y=2)

Created by the typecheck checker.

  unexpected-special-method-signature / E0302

Message emitted:

The special method %r expects %s param(s), %d %s given

Description:

Emitted when a special method was defined with an invalid number of parameters. If it has too few or too many, it might not work at all.

Problematic code:

class ContextManager:
    def __enter__(self, context):  # [unexpected-special-method-signature]
        pass
    def __exit__(self, type):  # [unexpected-special-method-signature]
        pass

Correct code:

class ContextManager:
    def __enter__(self):
        pass
    def __exit__(self, type, value, traceback):
        pass

Created by the classes checker.

  unhashable-member / E1143

Message emitted:

'%s' is unhashable and can't be used as a %s in a %s

Description:

Emitted when a dict key or set member is not hashable (i.e. doesn't define __hash__ method).

Problematic code:

# Print the number of apples:
print({"apple": 42}[["apple"]])  # [unhashable-member]

Correct code:

# Print the number of apples:
print({"apple": 42}["apple"])

Created by the typecheck checker.

  unpacking-non-sequence / E0633

Message emitted:

Attempting to unpack a non-sequence%s

Description:

Used when something which is not a sequence is used in an unpack assignment

Problematic code:

a, b, c = 1  # [unpacking-non-sequence]

Correct code:

a, b, c = 1, 2, 3

Created by the variables checker.

  unrecognized-inline-option / E0011

Message emitted:

Unrecognized file option %r

Description:

Used when an unknown inline option is encountered.

Problematic code:

# +1: [unrecognized-inline-option]
# pylint:applesoranges=1

Correct code:

# pylint: enable=too-many-public-methods

Created by the main checker.

  unrecognized-option / E0015

Message emitted:

Unrecognized option found: %s

Description:

Used when we detect an option that we do not recognize.

Correct code:

# This is a placeholder for correct code for this message.

Additional details:

You can help us make the doc better by contributing !

Created by the main checker.

  unsubscriptable-object / E1136

Message emitted:

Value '%s' is unsubscriptable

Description:

Emitted when a subscripted value doesn't support subscription (i.e. doesn't define __getitem__ method or __class_getitem__ for a class).

Problematic code:

class Fruit:
    pass
Fruit()[1]  # [unsubscriptable-object]

Correct code:

class Fruit:
    def __init__(self):
        self.colors = ["red", "orange", "yellow"]
    def __getitem__(self, idx):
        return self.colors[idx]
Fruit()[1]

Created by the typecheck checker.

  unsupported-assignment-operation / E1137

Message emitted:

%r does not support item assignment

Description:

Emitted when an object does not support item assignment (i.e. doesn't define __setitem__ method).

Problematic code:

def pick_fruits(fruits):
    for fruit in fruits:
        print(fruit)
pick_fruits(["apple"])[0] = "orange"  # [unsupported-assignment-operation]

Correct code:

def pick_fruits(fruits):
    for fruit in fruits:
        print(fruit)
    return []
pick_fruits(["apple"])[0] = "orange"

Created by the typecheck checker.

  unsupported-binary-operation / E1131

Message emitted:

%s

Description:

Emitted when a binary arithmetic operation between two operands is not supported.

Problematic code:

drink = "water" | None  # [unsupported-binary-operation]
result = [] | None  # [unsupported-binary-operation]

Correct code:

masked = 0b111111 & 0b001100
result = 0xaeff | 0x0b99

Configuration file:

[main]
py-version=3.9

Created by the typecheck checker.

  unsupported-delete-operation / E1138

Message emitted:

%r does not support item deletion

Description:

Emitted when an object does not support item deletion (i.e. doesn't define __delitem__ method).

Problematic code:

FRUITS = ("apple", "orange", "berry")
del FRUITS[0]  # [unsupported-delete-operation]

Correct code:

FRUITS = ["apple", "orange", "berry"]
del FRUITS[0]

Created by the typecheck checker.

  unsupported-membership-test / E1135

Message emitted:

Value '%s' doesn't support membership test

Description:

Emitted when an instance in membership test expression doesn't implement membership protocol (__contains__/__iter__/__getitem__).

Problematic code:

class Fruit:
    pass
apple = "apple" in Fruit()  # [unsupported-membership-test]

Correct code:

class Fruit:
    FRUITS = ["apple", "orange"]
    def __contains__(self, name):
        return name in self.FRUITS
apple = "apple" in Fruit()

Created by the typecheck checker.

  used-before-assignment / E0601

Message emitted:

Using variable %r before assignment

Description:

Emitted when a local variable is accessed before its assignment took place. Assignments in try blocks are assumed not to have occurred when evaluating associated except/finally blocks. Assignments in except blocks are assumed not to have occurred when evaluating statements outside the block, except when the associated try block contains a return statement.

Problematic code:

print(hello)  # [used-before-assignment]
hello = "Hello World !"

Correct code:

hello = "Hello World !"
print(hello)

Created by the variables checker.

  used-prior-global-declaration / E0118

Message emitted:

Name %r is used prior to global declaration

Description:

Emitted when a name is used prior a global declaration, which results in an error since Python 3.6.

Problematic code:

TOMATO = "black cherry"
def update_tomato():
    print(TOMATO)  # [used-prior-global-declaration]
    global TOMATO
    TOMATO = "cherry tomato"

Correct code:

TOMATO = "black cherry"
def update_tomato():
    global TOMATO
    TOMATO = "moneymaker"

Created by the basic checker.

  yield-inside-async-function / E1700

Message emitted:

Yield inside async function

Description:

Used when an `yield` or `yield from` statement is found inside an async function.

Problematic code:

async def foo():
    yield from [1, 2, 3]  # [yield-inside-async-function]

Correct code:

async def foo():
    def _inner_foo():
        yield from [1, 2, 3]
async def foo():
    yield 42

Additional details:

The message can't be emitted when using Python < 3.5.

Related links:

•   PEP 525

    Created by the async checker.

  yield-outside-function / E0105

Message emitted:

Yield outside function

Description:

Used when a "yield" statement is found outside a function or method.

Problematic code:

for i in range(10):
    yield i  # [yield-outside-function]

Correct code:

def one_to_ten():
    for i in range(10):
        yield i

Created by the basic checker.

All renamed messages in the error category:

  bad-context-manager / E0235

'bad-context-manager' has been renamed. The new message can be found at:

  bad-exception-context / E0703

'bad-exception-context' has been renamed. The new message can be found at:

  bad-option-value / E0012

'bad-option-value' has been renamed. The new message can be found at:

  useless-option-value / R0022

Message emitted:

Useless option value for '%s', %s

Description:

Used when a value for an option that is now deleted from pylint is encountered.

Problematic code:

"""'bad-continuation' was removed from pylint in https://github.com/PyCQA/pylint/pull/3571"""
# pylint: disable=bad-continuation  # [useless-option-value]

Correct code:

"""'bad-continuation' was removed from pylint in https://github.com/PyCQA/pylint/pull/3571"""

Additional details:

You can disable this check if you don't want to cleanup your configuration of old messages.

Created by the main checker.

  unknown-option-value / W0012

Message emitted:

Unknown option value for '%s', expected a valid pylint message and got '%s'

Description:

Used when an unknown value is encountered for an option.

Problematic code:

# pylint: disable=missnig-docstring  # [unknown-option-value]

Correct code:

# pylint: disable=missing-docstring

Created by the main checker.

  maybe-no-member / E1103

'maybe-no-member' has been renamed. The new message can be found at:

  old-non-iterator-returned-2 / E0234

'old-non-iterator-returned-2' has been renamed. The new message can be found at:

  old-unbalanced-tuple-unpacking / E0632

'old-unbalanced-tuple-unpacking' has been renamed. The new message can be found at:

  unbalanced-tuple-unpacking / W0632

Message emitted:

Possible unbalanced tuple unpacking with sequence %s: left side has %d label%s, right side has %d value%s

Description:

Used when there is an unbalanced tuple unpacking in assignment

Problematic code:

fruits = ("orange", "apple", "strawberry", "peer")
orange, apple, strawberry = fruits  # [unbalanced-tuple-unpacking]

Correct code:

fruits = ("orange", "apple", "strawberry", "peer")
orange, apple, *remaining_fruits = fruits

Related links:

•   PEP 3132 - Extended Iterable Unpacking

    Created by the variables checker.

  unhashable-dict-key / E1140

'unhashable-dict-key' has been renamed. The new message can be found at:

  Warning

All messages in the warning category:

  abstract-method / W0223

Message emitted:

Method %r is abstract in class %r but is not overridden in child class %r

Description:

Used when an abstract method (i.e. raise NotImplementedError) is not overridden in concrete class.

Problematic code:

class Pet:
    def make_sound(self):
        raise NotImplementedError
class Cat(Pet):  # [abstract-method]
    pass
import abc
class WildAnimal:
    @abc.abstractmethod
    def make_sound(self):
        pass
class Panther(WildAnimal):  # [abstract-method]
    pass

Correct code:

class Pet:
    def make_sound(self):
        raise NotImplementedError
class Cat(Pet):
    def make_sound(self):
        print("Meeeow")
import abc
class WildAnimal:
    @abc.abstractmethod
    def make_sound(self):
        pass
class Panther(WildAnimal):
    def make_sound(self):
        print("MEEEOW")

Created by the classes checker.

  anomalous-backslash-in-string / W1401

Message emitted:

Anomalous backslash in string: '%s'. String constant might be missing an r prefix.

Description:

Used when a backslash is in a literal string but not as an escape.

Problematic code:

string = "\z"  # [anomalous-backslash-in-string]

Correct code:

string = r"\z"
string = "\n"

Created by the string checker.

  anomalous-unicode-escape-in-string / W1402

Message emitted:

Anomalous Unicode escape in byte string: '%s'. String constant might be missing an r or u prefix.

Description:

Used when an escape like u is encountered in a byte string where it has no effect.

Problematic code:

print(b"\u%b" % b"0394")  # [anomalous-unicode-escape-in-string]

Correct code:

print(b"\\u%b" % b"0394")

Created by the string checker.

  arguments-differ / W0221

Message emitted:

%s %s %r method

Description:

Used when a method has a different number of arguments than in the implemented interface or in an overridden method. Extra arguments with default values are ignored.

Problematic code:

class Drink:
    def mix(self, fluid_one, fluid_two):
        return fluid_one + fluid_two
class Cocktail(Drink):
    def mix(self, fluid_one, fluid_two, alcoholic_fluid_one):  # [arguments-differ]
        return fluid_one + fluid_two + alcoholic_fluid_one
class Car:
    tank = 0
    def fill_tank(self, gas):
        self.tank += gas
class Airplane(Car):
    kerosene_tank = 0
    def fill_tank(self, gas, kerosene):  # [arguments-differ]
        self.tank += gas
        self.kerosene_tank += kerosene

Correct code:

class Drink:
    def mix(self, fluid_one, fluid_two):
        return fluid_one + fluid_two
class Cocktail(Drink):
    def mix(self, fluid_one, fluid_two, alcoholic_fluid_one="Beer"):
        return fluid_one + fluid_two + alcoholic_fluid_one
class Car:
    tank = 0
    def fill_tank(self, gas):
        self.tank += gas
class Airplane:
    tank = 0
    kerosene_tank = 0
    def fill_tank(self, gas, kerosene):
        self.tank += gas
        self.kerosene_tank += kerosene

Additional details:

argument-differ denotes an issue with the Liskov Substitution Principle. This means that the code in question violates an important design principle which does not have one single solution. We recommend to search online for the best solution in your case.

To give some examples of potential solutions: - Add the argument to the parent class - Remove the inheritance completely - Add default arguments to the child class

Related links:

•   Liskov Substitution Principle

    Created by the classes checker.

  arguments-out-of-order / W1114

Message emitted:

Positional arguments appear to be out of order

Description:

Emitted when the caller's argument names fully match the parameter names in the function signature but do not have the same order.

Problematic code:

def function_3_args(first_argument, second_argument, third_argument):
    """Three arguments function"""
    return first_argument, second_argument, third_argument
def args_out_of_order():
    first_argument = 1
    second_argument = 2
    third_argument = 3
    function_3_args(  # [arguments-out-of-order]
        first_argument, third_argument, second_argument
    )

Correct code:

def function_3_args(first_argument, second_argument, third_argument):
    """Three arguments function"""
    return first_argument, second_argument, third_argument
def args_out_of_order():
    first_argument = 1
    second_argument = 2
    third_argument = 3
    function_3_args(first_argument, second_argument, third_argument)

Created by the typecheck checker.

  arguments-renamed / W0237

Message emitted:

%s %s %r method

Description:

Used when a method parameter has a different name than in the implemented interface or in an overridden method.

Problematic code:

class Fruit:
    def brew(self, ingredient_name: str):
        print(f"Brewing a {type(self)} with {ingredient_name}")
class Apple(Fruit):
    ...
class Orange(Fruit):
    def brew(self, flavor: str):  # [arguments-renamed]
        print(f"Brewing an orange with {flavor}")
for fruit, ingredient_name in [[Orange(), "thyme"], [Apple(), "cinnamon"]]:
    fruit.brew(ingredient_name=ingredient_name)

Correct code:

class Fruit:
    def brew(self, ingredient_name: str):
        print(f"Brewing a {type(self)} with {ingredient_name}")
class Apple(Fruit):
    ...
class Orange(Fruit):
    def brew(self, ingredient_name: str):
        print(f"Brewing an orange with {ingredient_name}")
for fruit, ingredient_name in [[Orange(), "thyme"], [Apple(), "cinnamon"]]:
    fruit.brew(ingredient_name=ingredient_name)

Created by the classes checker.

  assert-on-string-literal / W0129

Message emitted:

Assert statement has a string literal as its first argument. The assert will %s fail.

Description:

Used when an assert statement has a string literal as its first argument, which will cause the assert to always pass.

Problematic code:

def test_division():
    a = 9 / 3
    assert "No ZeroDivisionError were raised"  # [assert-on-string-literal]

Correct code:

def test_division():
    a = 9 / 3
    assert a == 3

Additional details:

Directly asserting a string literal will always pass. The solution is to test something that could fail, or not assert at all.

For unittest assertions there is the similar redundant-unittest-assert / W1503 message.

Related links:

•   Tests without assertion

•   Testing that there is no error raised

•   Parametrizing conditional raising

    Created by the basic checker.

  assert-on-tuple / W0199

Message emitted:

Assert called on a populated tuple. Did you mean 'assert x,y'?

Description:

A call of assert on a tuple will always evaluate to true if the tuple is not empty, and will always evaluate to false if it is.

Problematic code:

assert (1, None)  # [assert-on-tuple]

Correct code:

x, y = (1, None)
assert x
assert y

Additional details:

Directly asserting a non-empty tuple will always pass. The solution is to
    test something that could fail, or not assert at all.

    For unittest assertions there is the similar redundant-unittest-assert / W1503 message.

    Created by the basic checker.

  attribute-defined-outside-init / W0201

Message emitted:

Attribute %r defined outside __init__

Description:

Used when an instance attribute is defined outside the __init__ method.

Problematic code:

class Student:
    def register(self):
        self.is_registered = True  # [attribute-defined-outside-init]

Correct code:

class Student:
    def __init__(self):
        self.is_registered = False
    def register(self):
        self.is_registered = True

Created by the classes checker.

  bad-builtin / W0141

Message emitted:

Used builtin function %s

Description:

Used when a disallowed builtin function is used (see the bad-function option). Usual disallowed functions are the ones like map, or filter , where Python offers now some cleaner alternative like list comprehension.

Problematic code:

numbers = list(map(lambda x: 2 * x, [1, 2, 3]))  # [bad-builtin]
print(numbers)

Correct code:

numbers = [2 * x for x in [1, 2, 3]]
print(numbers)

Configuration file:

[MAIN]
load-plugins = pylint.extensions.bad_builtin

NOTE:

This message is emitted by the optional 'deprecated_builtins'
    checker which requires the pylint.extensions.bad_builtin plugin to be loaded.

    Created by the deprecated_builtins checker.

  bad-chained-comparison / W3601

Message emitted:

Suspicious %s-part chained comparison using semantically incompatible operators (%s)

Description:

Used when there is a chained comparison where one expression is part of two comparisons that belong to different semantic groups ("<" does not mean the same thing as "is", chaining them in "0 < x is None" is probably a mistake).

Problematic code:

def xor_check(*, left=None, right=None):
    if left is None != right is None:  # [bad-chained-comparison]
        raise ValueError('Either both left= and right= need to be provided or none should.')

Correct code:

def xor_check(*, left=None, right=None):
    if (left is None) != (right is None):
        raise ValueError('Either both left= and right= need to be provided or none should.')

Related links:

•   Comparison Chaining

    Created by the bad-chained-comparison checker.

  bad-dunder-name / W3201

Message emitted:

Bad or misspelled dunder method name %s.

Description:

Used when a dunder method is misspelled or defined with a name not within the predefined list of dunder names.

Problematic code:

class Apples:
    def _init_(self):  # [bad-dunder-name]
        pass
    def __hello__(self):  # [bad-dunder-name]
        print("hello")

Correct code:

class Apples:
    def __init__(self):
        pass
    def hello(self):
        print("hello")

Configuration file:

[MAIN]
load-plugins=pylint.extensions.dunder

NOTE:

This message is emitted by the optional 'dunder'
    checker which requires the pylint.extensions.dunder plugin to be loaded.

    Created by the dunder checker.

  bad-format-string / W1302

Message emitted:

Invalid format string

Description:

Used when a PEP 3101 format string is invalid.

Problematic code:

print('{a[0] + a[1]}'.format(a=[0, 1])) # [bad-format-string]

Correct code:

print('{a[0]} + {a[1]}'.format(a=[0, 1]))

Related links:

•   Format String Syntax

•   PyFormat

    Created by the string checker.

  bad-format-string-key / W1300

Message emitted:

Format string dictionary key should be a string, not %s

Description:

Used when a format string that uses named conversion specifiers is used with a dictionary whose keys are not all strings.

Problematic code:

print("%(one)d" % {"one": 1, 2: 2})  # [bad-format-string-key]

Correct code:

print("%(one)d, %(two)d" % {"one": 1, "two": 2})

Additional details:

This check only works for old-style string formatting using the '%' operator.

This check only works if the dictionary with the values to be formatted is defined inline. Passing a variable will not trigger the check as the other keys in this dictionary may be used in other contexts, while an inline defined dictionary is clearly only intended to hold the values that should be formatted.

Created by the string checker.

  bad-indentation / W0311

Message emitted:

Bad indentation. Found %s %s, expected %s

Description:

Used when an unexpected number of indentation's tabulations or spaces has been found.

Problematic code:

if input():
   print('yes')  # [bad-indentation]

Correct code:

if input():
    print('yes')

Additional details:

The option --indent-string can be used to set the indentation unit for this check.

Created by the format checker.

  bad-open-mode / W1501

Message emitted:

"%s" is not a valid mode for open.

Description:

Python supports: r, w, a[, x] modes with b, +, and U (only with r) options. See https://docs.python.org/3/library/functions.html#open

Problematic code:

def foo(file_path):
    with open(file_path, "rwx") as file:  # [bad-open-mode]
        contents = file.read()

Correct code:

def foo(file_path):
    with open(file_path, "r") as file:
        contents = file.read()

Created by the stdlib checker.

  bad-staticmethod-argument / W0211

Message emitted:

Static method with %r as first argument

Description:

Used when a static method has "self" or a value specified in valid-classmethod-first-arg option or valid-metaclass-classmethod-first-arg option as first argument.

Problematic code:

class Wolf:
    @staticmethod
    def eat(self):  # [bad-staticmethod-argument]
        pass

Correct code:

class Wolf:
    @staticmethod
    def eat(sheep):
        pass

Created by the classes checker.

  bad-thread-instantiation / W1506

Message emitted:

threading.Thread needs the target function

Description:

The warning is emitted when a threading.Thread class is instantiated without the target function being passed as a kwarg or as a second argument. By default, the first parameter is the group param, not the target param.

Problematic code:

import threading
def thread_target(n):
    print(n ** 2)
thread = threading.Thread(lambda: None)  # [bad-thread-instantiation]
thread.start()

Correct code:

import threading
def thread_target(n):
    print(n ** 2)
thread = threading.Thread(target=thread_target, args=(10,))
thread.start()

Created by the stdlib checker.

  bare-except / W0702

Message emitted:

No exception type(s) specified

Description:

A bare ``except:`` clause will catch ``SystemExit`` and ``KeyboardInterrupt`` exceptions, making it harder to interrupt a program with ``Control-C``, and can disguise other problems. If you want to catch all exceptions that signal program errors, use ``except Exception:`` (bare except is equivalent to ``except BaseException:``).

Problematic code:

try:
    import platform_specific_module
except:  # [bare-except]
    platform_specific_module = None

Correct code:

try:
    import platform_specific_module
except ImportError:
    platform_specific_module = None

Additional details:

A good rule of thumb is to limit use of bare ‘except’ clauses to two cases: - If the exception handler will be printing out or logging the traceback; at least the user will be aware that an error has occurred. - If the code needs to do some cleanup work, but then lets the exception propagate upwards with raise. try...finally can be a better way to handle this case.

Related links:

•   Programming recommendation in PEP8

    Created by the exceptions checker.

  binary-op-exception / W0711

Message emitted:

Exception to catch is the result of a binary "%s" operation

Description:

Used when the exception to catch is of the form "except A or B:". If intending to catch multiple, rewrite as "except (A, B):"

Problematic code:

try:
    1 / 0
except ZeroDivisionError or ValueError:  # [binary-op-exception]
    pass

Correct code:

try:
    1 / 0
except (ZeroDivisionError, ValueError):
    pass

Created by the exceptions checker.

  boolean-datetime / W1502

Message emitted:

Using datetime.time in a boolean context.

Description:

Using datetime.time in a boolean context can hide subtle bugs when the time they represent matches midnight UTC. This behaviour was fixed in Python 3.5. See https://bugs.python.org/issue13936 for reference.

Problematic code:

import datetime
if datetime.time():  # [boolean-datetime]
    print("It is time.")
if datetime.datetime.now().time():  # [boolean-datetime]
    print("Now or never.")

Correct code:

import datetime
time_now_utc = datetime.datetime.now(tz=datetime.UTC).time()
if time_now_utc > datetime.time(6, 0):
    print("Daytime!")
if time_now_utc < datetime.time(6, 0):
    print("Nighttime!")

Configuration file:

[main]
py-version=3.4

Related links:

•   Python bug tracker

    Created by the stdlib checker.

  broad-exception-caught / W0718

Message emitted:

Catching too general exception %s

Description:

If you use a naked ``except Exception:`` clause, you might end up catching exceptions other than the ones you expect to catch. This can hide bugs or make it harder to debug programs when unrelated errors are hidden.

Problematic code:

try:
    import platform_specific_module
except Exception:  # [broad-exception-caught]
    platform_specific_module = None

Correct code:

try:
    import platform_specific_module
except ImportError:
    platform_specific_module = None

Additional details:

For example, you're trying to import a library with required system dependencies and you catch everything instead of only import errors, you will miss the error message telling you, that your code could work if you had installed the system dependencies.

Related links:

•   Should I always specify an exception type in 'except' statements?

    Created by the exceptions checker.

  broad-exception-raised / W0719

Message emitted:

Raising too general exception: %s

Description:

Raising exceptions that are too generic force you to catch exceptions generically too. It will force you to use a naked ``except Exception:`` clause. You might then end up catching exceptions other than the ones you expect to catch. This can hide bugs or make it harder to debug programs when unrelated errors are hidden.

Problematic code:

def small_apple(apple, length):
    if len(apple) < length:
        raise Exception("Apple is too small!")  # [broad-exception-raised]
    print(f"{apple} is proper size.")

Correct code:

def small_apple(apple, length):
    if len(apple) < length:
        raise ValueError("Apple is too small!")
    print(f"{apple} is proper size.")

Related links:

•   Programming recommendation in PEP8

    Created by the exceptions checker.

  cell-var-from-loop / W0640

Message emitted:

Cell variable %s defined in loop

Description:

A variable used in a closure is defined in a loop. This will result in all closures using the same value for the closed-over variable.

Problematic code:

def foo(numbers):
    for i in numbers:
        def bar():
            print(i)  # [cell-var-from-loop]
        bar()

Correct code:

def bar(x):
    print(x)
def foo(numbers):
    for i in numbers:
        bar(i)

Related links:

•   Stackoverflow discussion

    Created by the variables checker.

  comparison-with-callable / W0143

Message emitted:

Comparing against a callable, did you omit the parenthesis?

Description:

This message is emitted when pylint detects that a comparison with a callable was made, which might suggest that some parenthesis were omitted, resulting in potential unwanted behaviour.

Problematic code:

def function_returning_a_fruit() -> str:
    return "orange"
def is_an_orange(fruit: str = "apple"):
    # apple == <function function_returning_a_fruit at 0x7f343ff0a1f0>
    return fruit == function_returning_a_fruit  # [comparison-with-callable]

Correct code:

def function_returning_a_fruit() -> str:
    return "orange"
def is_an_orange(fruit: str = "apple"):
    # apple == orange
    return fruit == function_returning_a_fruit()

Created by the basic checker.

  confusing-with-statement / W0124

Message emitted:

Following "as" with another context manager looks like a tuple.

Description:

Emitted when a `with` statement component returns multiple values and uses name binding with `as` only for a part of those values, as in with ctx() as a, b. This can be misleading, since it's not clear if the context manager returns a tuple or if the node without a name binding is another context manager.

Problematic code:

with open('file.txt', 'w') as fh1, fh2:  # [confusing-with-statement]
    pass

Correct code:

with open('file.txt', 'w', encoding="utf8") as fh1:
    with open('file.txt', 'w', encoding="utf8") as fh2:
        pass

Created by the basic checker.

  consider-ternary-expression / W0160

Message emitted:

Consider rewriting as a ternary expression

Description:

Multiple assign statements spread across if/else blocks can be rewritten with a single assignment and ternary expression

Problematic code:

x, y = input(), input()
if x >= y:  # [consider-ternary-expression]
    maximum = x
else:
    maximum = y

Correct code:

x, y = input(), input()
maximum = x if x >= y else y

Configuration file:

[MAIN]
load-plugins=pylint.extensions.consider_ternary_expression

NOTE:

This message is emitted by the optional 'consider_ternary_expression'
    checker which requires the pylint.extensions.consider_ternary_expression plugin to be loaded.

    Created by the consider_ternary_expression checker.

  dangerous-default-value / W0102

Message emitted:

Dangerous default value %s as argument

Description:

Used when a mutable value as list or dictionary is detected in a default value for an argument.

Problematic code:

def whats_on_the_telly(penguin=[]):  # [dangerous-default-value]
    penguin.append("property of the zoo")
    return penguin

Correct code:

def whats_on_the_telly(penguin=None):
    if penguin is None:
        penguin = []
    penguin.append("property of the zoo")
    return penguin

Additional details:

With a mutable default value, with each call the default value is modified, i.e.:

whats_on_the_telly() # ["property of the zoo"]
whats_on_the_telly() # ["property of the zoo", "property of the zoo"]
whats_on_the_telly() # ["property of the zoo", "property of the zoo", "property of the zoo"]

Created by the basic checker.

  deprecated-argument / W4903

Message emitted:

Using deprecated argument %s of method %s()

Description:

The argument is marked as deprecated and will be removed in the future.

Correct code:

# This is a placeholder for correct code for this message.

Additional details:

The actual replacement need to be studied on a case by case basis by reading the deprecation warning or the release notes.

Created by the stdlib checker.

  deprecated-class / W4904

Message emitted:

Using deprecated class %s of module %s

Description:

The class is marked as deprecated and will be removed in the future.

Problematic code:

from collections import Iterable  # [deprecated-class]

Correct code:

from collections.abc import Iterable

Additional details:

The actual replacement need to be studied on a case by case basis by reading the deprecation warning or the release notes.

Created by the stdlib checker.

  deprecated-decorator / W4905

Message emitted:

Using deprecated decorator %s()

Description:

The decorator is marked as deprecated and will be removed in the future.

Problematic code:

import abc
class Animal:
    @abc.abstractclassmethod  # [deprecated-decorator]
    def breath(cls):
        pass

Correct code:

import abc
class Animal:
    @abc.classmethod
    @abc.abstractmethod
    def breath(cls):
        pass

Configuration file:

[main]
py-version = 3.3

Additional details:

The actual replacement need to be studied on a case by case basis by reading the deprecation warning or the release notes.

Created by the stdlib checker.

  deprecated-method / W4902

Message emitted:

Using deprecated method %s()

Description:

The method is marked as deprecated and will be removed in the future.

Problematic code:

import logging
logging.warn("I'm coming, world !") # [deprecated-method]

Correct code:

import logging
logging.warning("I'm coming, world !")

Additional details:

The actual replacement need to be studied on a case by case basis by reading the deprecation warning or the release notes.

Created by the stdlib checker.

  deprecated-module / W4901

Message emitted:

Deprecated module %r

Description:

A module marked as deprecated is imported.

Problematic code:

import distutils  # [deprecated-module]
import whatever_you_want  # [deprecated-module]

Correct code:

import setuptools
import whatever_replacement_you_want

Configuration file:

[main]
py-version=3.7
deprecated-modules=whatever_you_want

Additional details:

The actual replacement need to be studied on a case by case basis by reading the deprecation warning or the release notes.

Created by the imports checker.

  deprecated-typing-alias / W6001

Message emitted:

'%s' is deprecated, use '%s' instead

Description:

Emitted when a deprecated typing alias is used.

Problematic code:

import typing
item_to_number_of_item: typing.Dict[str, int]  # [deprecated-typing-alias]

Correct code:

item_to_number_of_item: dict[str, int]

Configuration file:

[main]
load-plugins = pylint.extensions.typing

NOTE:

This message is emitted by the optional 'typing'
    checker which requires the pylint.extensions.typing plugin to be loaded.

    Created by the typing checker.

  differing-param-doc / W9017

Message emitted:

"%s" differing in parameter documentation

Description:

Please check parameter names in declarations.

Problematic code:

def foo(x, y):  # [differing-param-doc]
    """A dummy string.
    :param int x: x value.
    :param int z: z value.
    """
    return x + y

Correct code:

def foo(x, y):
    """A dummy string.
    :param int x: x value.
    :param int y: y value.
    """
    return x + y

Configuration file:

[MAIN]
load-plugins = pylint.extensions.docparams

NOTE:

This message is emitted by the optional 'parameter_documentation'
    checker which requires the pylint.extensions.docparams plugin to be loaded.

    Created by the parameter_documentation checker.

  differing-type-doc / W9018

Message emitted:

"%s" differing in parameter type documentation

Description:

Please check parameter names in type declarations.

Problematic code:

def foo(x: int, y: int):  # [differing-type-doc]
    """A dummy string.
    :param int xy: x value.
    :param str y: y value.
    """
    return x + y

Correct code:

def foo(x, y):
    """A dummy string.
    :param int x: x value.
    :param int y: y value.
    """
    return x + y

Configuration file:

[MAIN]
load-plugins = pylint.extensions.docparams

NOTE:

This message is emitted by the optional 'parameter_documentation'
    checker which requires the pylint.extensions.docparams plugin to be loaded.

    Created by the parameter_documentation checker.

  duplicate-except / W0705

Message emitted:

Catching previously caught exception type %s

Description:

Used when an except catches a type that was already caught by a previous handler.

Problematic code:

try:
    1 / 0
except ZeroDivisionError:
    pass
except ZeroDivisionError:  # [duplicate-except]
    pass

Correct code:

try:
    1 / 0
except ZeroDivisionError:
    pass

Created by the exceptions checker.

  duplicate-key / W0109

Message emitted:

Duplicate key %r in dictionary

Description:

Used when a dictionary expression binds the same key multiple times.

Problematic code:

test_score = {"Mathematics": 85, "Biology": 90, "Mathematics": 75}  # [duplicate-key]

Correct code:

test_score = {"Mathematics": 85, "Biology": 90, "History": 75}

Related links:

•   Python Dictionaries

•   Mapping Types — dict

    Created by the basic checker.

  duplicate-string-formatting-argument / W1308

Message emitted:

Duplicate string formatting argument %r, consider passing as named argument

Description:

Used when we detect that a string formatting is repeating an argument instead of using named string arguments

Problematic code:

# pylint: disable=missing-docstring, consider-using-f-string
SEE = "see 👀"
SEA = "sea 🌊"
# +1: [duplicate-string-formatting-argument,duplicate-string-formatting-argument]
CONST = """
A sailor went to {}, {}, {}
To {} what he could {}, {}, {}
But all that he could {}, {}, {}
Was the bottom of the deep blue {}, {}, {}!
""".format(
    SEA,
    SEA,
    SEA,
    SEE,
    SEE,
    SEE,
    SEE,
    SEE,
    SEE,
    SEE,
    SEA,
    SEA,
    SEA,
)

Correct code:

# pylint: disable=missing-docstring, consider-using-f-string
SEE = "see 👀"
SEA = "sea 🌊"
CONST = """
A sailor went to {sea}, {sea}, {sea}
To {see} what he could {see}, {see}, {see}
But all that he could {see}, {see}, {see}
Was the bottom of the deep blue {sea}, {sea}, {sea}!
""".format(
    sea=SEA, see=SEE
)

Created by the string checker.

  duplicate-value / W0130

Message emitted:

Duplicate value %r in set

Description:

This message is emitted when a set contains the same value two or more times.

Problematic code:

incorrect_set = {'value1', 23, 5, 'value1'} # [duplicate-value]

Correct code:

correct_set = {'value1', 23, 5}

Created by the basic checker.

  eq-without-hash / W1641

Message emitted:

Implementing __eq__ without also implementing __hash__

Description:

Used when a class implements __eq__ but not __hash__. Objects get None as their default __hash__ implementation if they also implement __eq__.

Problematic code:

class Fruit:  # [eq-without-hash]
    def __init__(self) -> None:
        self.name = "apple"
    def __eq__(self, other: object) -> bool:
        return isinstance(other, Fruit) and other.name == self.name

Correct code:

class Fruit:
    def __init__(self) -> None:
        self.name = "apple"
    def __eq__(self, other: object) -> bool:
        return isinstance(other, Fruit) and other.name == self.name
    def __hash__(self) -> int:
        return hash(self.name)

Configuration file:

[MAIN]
load-plugins=pylint.extensions.eq_without_hash,

NOTE:

This message is emitted by the optional 'eq-without-hash'
    checker which requires the pylint.extensions.eq_without_hash plugin to be loaded.

    Created by the eq-without-hash checker.

  eval-used / W0123

Message emitted:

Use of eval

Description:

Used when you use the "eval" function, to discourage its usage. Consider using `ast.literal_eval` for safely evaluating strings containing Python expressions from untrusted sources.

Problematic code:

eval("[1, 2, 3]")  # [eval-used]

Correct code:

from ast import literal_eval
literal_eval("[1, 2, 3]")

Created by the basic checker.

  exec-used / W0122

Message emitted:

Use of exec

Description:

Raised when the 'exec' statement is used. It's dangerous to use this function for a user input, and it's also slower than actual code in general. This doesn't mean you should never use it, but you should consider alternatives first and restrict the functions available.

Problematic code:

username = "Ada"
code_to_execute = f"""input('Enter code to be executed please, {username}: ')"""
program = exec(code_to_execute)  # [exec-used]
exec(program)  # [exec-used]

Correct code:

def get_user_code(name):
    return input(f'Enter code to be executed please, {name}: ')
username = "Ada"
allowed_globals = {'__builtins__' : None}
allowed_locals = {'print': print}
exec(get_user_code(username), allowed_globals, allowed_locals)  # pylint: disable=exec-used

Additional details:

The available methods and variables used in exec() may introduce a security hole. You can restrict the use of these variables and methods by passing optional globals and locals parameters (dictionaries) to the exec() method.

However, use of exec is still insecure. For example, consider the following call that writes a file to the user's system:

exec("""\nwith open("file.txt", "w", encoding="utf-8") as file:\n file.write("# code as nefarious as imaginable")\n""")

Related links:

•   Be careful with exec and eval in Python

    Created by the basic checker.

  expression-not-assigned / W0106

Message emitted:

Expression "%s" is assigned to nothing

Description:

Used when an expression that is not a function call is assigned to nothing. Probably something else was intended.

Problematic code:

str(42) == "42"  # [expression-not-assigned]

Correct code:

are_equal: bool = str(42) == "42"

Created by the basic checker.

  f-string-without-interpolation / W1309

Message emitted:

Using an f-string that does not have any interpolated variables

Description:

Used when we detect an f-string that does not use any interpolation variables, in which case it can be either a normal string or a bug in the code.

Problematic code:

x = 1
y = 2
print(f"x + y = x + y")  # [f-string-without-interpolation]

Correct code:

x = 1
y = 2
print(f"{x} + {y} = {x + y}")

Created by the string checker.

  fixme / W0511

Message emitted:

%s

Description:

Used when a warning note as FIXME or XXX is detected.

Problematic code:

# FIXME: Create an issue on the bug tracker for this refactor we might do someday  # [fixme]
...
# TODO: We should also fix this at some point  # [fixme]

Correct code:

# I no longer want to fix this
...
# I have fixed the issue

Additional details:

You can get use regular expressions and the notes-rgx option to create some constraints for this message. See the following issue for some examples.

Created by the miscellaneous checker.

  forgotten-debug-statement / W1515

Message emitted:

Leaving functions creating breakpoints in production code is not recommended

Description:

Calls to breakpoint(), sys.breakpointhook() and pdb.set_trace() should be removed from code that is not actively being debugged.

Problematic code:

import pdb
def find_the_treasure(clues):
    for clue in clues:
        pdb.set_trace() # [forgotten-debug-statement]
        if "treasure" in clue:
            return True
    return False
treasure_hunt = ["Dead Man's Chest", "X marks the spot", "The treasure is buried near the palm tree"]
find_the_treasure(treasure_hunt)

Correct code:

def find_the_treasure(clues):
    for clue in clues:
        if "treasure" in clue:
            return True
    return False
treasure_hunt = ["Dead Man's Chest", "X marks the spot", "The treasure is buried near the palm tree"]
find_the_treasure(treasure_hunt)

Created by the stdlib checker.

  format-combined-specification / W1305

Message emitted:

Format string contains both automatic field numbering and manual field specification

Description:

Used when a PEP 3101 format string contains both automatic field numbering (e.g. '{}') and manual field specification (e.g. '{0}').

Problematic code:

print('{} {1}'.format('hello', 'world'))  # [format-combined-specification]

Correct code:

print('{0} {1}'.format('hello', 'world'))
# or
print('{} {}'.format('hello', 'world'))

Created by the string checker.

  format-string-without-interpolation / W1310

Message emitted:

Using formatting for a string that does not have any interpolated variables

Description:

Used when we detect a string that does not have any interpolation variables, in which case it can be either a normal string without formatting or a bug in the code.

Problematic code:

print("number".format(1))  # [format-string-without-interpolation]

Correct code:

print("number: {}".format(1))

Created by the string checker.

  global-at-module-level / W0604

Message emitted:

Using the global statement at the module level

Description:

Used when you use the "global" statement at the module level since it has no effect.

Problematic code:

price = 25
global price  # [global-at-module-level]

Correct code:

price = 25

Related links:

•   Official Python FAQ - global and local

•   PEP 3104 - Access to Names in Outer Scopes

•   Python global statement

    Created by the variables checker.

  global-statement / W0603

Message emitted:

Using the global statement

Description:

Used when you use the "global" statement to update a global variable. Pylint discourages its usage. That doesn't mean you cannot use it!

Problematic code:

var = 1
def foo():
    global var  # [global-statement]
    var = 10
    print(var)
foo()
print(var)

Correct code:

var = 1
def foo():
    print(var)
    return 10
var = foo()
print(var)

Created by the variables checker.

  global-variable-not-assigned / W0602

Message emitted:

Using global for %r but no assignment is done

Description:

When a variable defined in the global scope is modified in an inner scope, the 'global' keyword is required in the inner scope only if there is an assignment operation done in the inner scope.

Problematic code:

TOMATO = "black cherry"
def update_tomato():
    global TOMATO  # [global-variable-not-assigned]
    print(TOMATO)

Correct code:

TOMATO = "black cherry"
def update_tomato():
    global TOMATO
    TOMATO = "moneymaker"

Created by the variables checker.

  global-variable-undefined / W0601

Message emitted:

Global variable %r undefined at the module level

Description:

Used when a variable is defined through the "global" statement but the variable is not defined in the module scope.

Problematic code:

def update_tomato():
    global TOMATO  # [global-variable-undefined]
    TOMATO = "moneymaker"

Correct code:

TOMATO = "black cherry"
def update_tomato():
    global TOMATO
    TOMATO = "moneymaker"

Created by the variables checker.

  implicit-flag-alias / W0213

Message emitted:

Flag member %(overlap)s shares bit positions with %(sources)s

Description:

Used when multiple integer values declared within an enum.IntFlag class share a common bit position.

Problematic code:

from enum import IntFlag
class FilePermissions(IntFlag):
    READ = 1
    WRITE = 2
    EXECUTE = 3  # [implicit-flag-alias]

Correct code:

from enum import IntFlag
class FilePermissions(IntFlag):
    READ = 1
    WRITE = 2
    EXECUTE = 4

Created by the classes checker.

  implicit-str-concat / W1404

Message emitted:

Implicit string concatenation found in %s

Description:

String literals are implicitly concatenated in a literal iterable definition : maybe a comma is missing ?

Problematic code:

x = ["a" "b"]  # [implicit-str-concat]
with open("hello.txt" "r") as f:  # [implicit-str-concat]
    print(f.read())

Correct code:

x = ["a", "b"]
with open("hello.txt", "r") as f:
    print(f.read())

Created by the string checker.

  import-self / W0406

Message emitted:

Module import itself

Description:

Used when a module is importing itself.

Additional details:

Say you have a file called my_file.py. import-self would be raised on the following code:

from my_file import a_function  # [import-self]
def a_function():
    pass

The solution would be to remove the import:

def a_function():
    pass

Created by the imports checker.

  inconsistent-quotes / W1405

Message emitted:

Quote delimiter %s is inconsistent with the rest of the file

Description:

Quote delimiters are not used consistently throughout a module (with allowances made for avoiding unnecessary escaping).

Problematic code:

import datetime
print('Current year: ', datetime.date.today().strftime("%Y")) # [inconsistent-quotes]

Correct code:

import datetime
print("Current year: ", datetime.date.today().strftime("%Y"))

Configuration file:

[main]
check-quote-consistency=yes

Created by the string checker.

  invalid-envvar-default / W1508

Message emitted:

%s default type is %s. Expected str or None.

Description:

Env manipulation functions return None or str values. Supplying anything different as a default may cause bugs. See https://docs.python.org/3/library/os.html#os.getenv.

Problematic code:

import os
env = os.getenv('SECRET_KEY', 1)  # [invalid-envvar-default]

Correct code:

import os
env = os.getenv('SECRET_KEY', '1')

Created by the stdlib checker.

  invalid-format-index / W1307

Message emitted:

Using invalid lookup key %r in format specifier %r

Description:

Used when a PEP 3101 format string uses a lookup specifier ({a[1]}), but the argument passed for formatting doesn't contain or doesn't have that key as an attribute.

Problematic code:

not_enough_fruits = ["apple"]
print('The second fruit is a {fruits[1]}'.format(fruits=not_enough_fruits))  # [invalid-format-index]

Correct code:

enough_fruits = ["apple", "banana"]
print('The second fruit is a {fruits[1]}'.format(fruits=enough_fruits))

Created by the string checker.

  invalid-overridden-method / W0236

Message emitted:

Method %r was expected to be %r, found it instead as %r

Description:

Used when we detect that a method was overridden in a way that does not match its base class which could result in potential bugs at runtime.

Problematic code:

class Fruit:
    async def bore(self, insect):
        insect.eat(self)
class Apple(Fruit):
    def bore(self, insect):  # [invalid-overridden-method]
        insect.eat(self)

Correct code:

class Fruit:
    async def bore(self, insect):
        insect.eat(self)
class Apple(Fruit):
    async def bore(self, insect):
        insect.eat(self)

Created by the classes checker.

  isinstance-second-argument-not-valid-type / W1116

Message emitted:

Second argument of isinstance is not a type

Description:

Emitted when the second argument of an isinstance call is not a type.

Problematic code:

isinstance("apples and oranges", hex)  # [isinstance-second-argument-not-valid-type]

Correct code:

isinstance("apples and oranges", str)

Created by the typecheck checker.

  keyword-arg-before-vararg / W1113

Message emitted:

Keyword argument before variable positional arguments list in the definition of %s function

Description:

When defining a keyword argument before variable positional arguments, one can end up in having multiple values passed for the aforementioned parameter in case the method is called with keyword arguments.

Problematic code:

def func(x=None, *args):  # [keyword-arg-before-vararg]
    return [x, *args]

Correct code:

def func(*args, x=None):
    return [*args, x]

Created by the typecheck checker.

  logging-format-interpolation / W1202

Message emitted:

Use %s formatting in logging functions

Description:

Used when a logging statement has a call form of "logging.<logging method>(format_string.format(format_args...))". Use another type of string formatting instead. You can use % formatting but leave interpolation to the logging function by passing the parameters as arguments. If logging-fstring-interpolation is disabled then you can use fstring formatting. If logging-not-lazy is disabled then you can use % formatting as normal.

Problematic code:

import logging
import sys
logging.error('Python version: {}'.format(sys.version))  # [logging-format-interpolation]

Correct code:

import logging
import sys
logging.error('Python version: %s', sys.version)

Additional details:

Another reasonable option is to use f-string. If you want to do that, you need to enable logging-format-interpolation and disable logging-fstring-interpolation.

Related links:

•   logging variable data

•   rational

    Created by the logging checker.

  logging-fstring-interpolation / W1203

Message emitted:

Use %s formatting in logging functions

Description:

Used when a logging statement has a call form of "logging.<logging method>(f"...")".Use another type of string formatting instead. You can use % formatting but leave interpolation to the logging function by passing the parameters as arguments. If logging-format-interpolation is disabled then you can use str.format. If logging-not-lazy is disabled then you can use % formatting as normal.

Problematic code:

import logging
import sys
logging.error(f'Python version: {sys.version}')  # [logging-fstring-interpolation]

Correct code:

import logging
import sys
logging.error('Python version: %s', sys.version)

Additional details:

This message permits to allow f-string in logging and still be warned of logging-format-interpolation.

Related links:

•   logging variable data

•   rational

    Created by the logging checker.

  logging-not-lazy / W1201

Message emitted:

Use %s formatting in logging functions

Description:

Used when a logging statement has a call form of "logging.<logging method>(format_string % (format_args...))". Use another type of string formatting instead. You can use % formatting but leave interpolation to the logging function by passing the parameters as arguments. If logging-fstring-interpolation is disabled then you can use fstring formatting. If logging-format-interpolation is disabled then you can use str.format.

Problematic code:

import logging
try:
    function()
except Exception as e:
    logging.error('Error occurred: %s' % e)  # [logging-not-lazy]
    raise

Correct code:

import logging
try:
    function()
except Exception as e:
    logging.error('Error occurred: %s', e)
    raise

Additional details:

Another reasonable option is to use f-strings. If you want to do that, you need to enable logging-not-lazy and disable logging-fstring-interpolation.

Related links:

•   Logging variable data

•   Rationale

    Created by the logging checker.

  lost-exception / W0150

Message emitted:

%s statement in finally block may swallow exception

Description:

Used when a break or a return statement is found inside the finally clause of a try...finally block: the exceptions raised in the try clause will be silently swallowed instead of being re-raised.

Problematic code:

class FasterThanTheSpeedOfLightError(ZeroDivisionError):
    def __init__(self):
        super().__init__("You can't go faster than the speed of light !")
def calculate_speed(distance: float, time: float) -> float:
    try:
        return distance / time
    except ZeroDivisionError as e:
        raise FasterThanTheSpeedOfLightError() from e
    finally:
        return 299792458  # [lost-exception]

Correct code:

class FasterThanTheSpeedOfLightError(ZeroDivisionError):
    def __init__(self):
        super().__init__("You can't go faster than the speed of light !")
def calculate_speed(distance: float, time: float) -> float:
    try:
        return distance / time
    except ZeroDivisionError as e:
        raise FasterThanTheSpeedOfLightError() from e

Created by the basic checker.

  method-cache-max-size-none / W1518

Message emitted:

'lru_cache(maxsize=None)' or 'cache' will keep all method args alive indefinitely, including 'self'

Description:

By decorating a method with lru_cache or cache the 'self' argument will be linked to the function and therefore never garbage collected. Unless your instance will never need to be garbage collected (singleton) it is recommended to refactor code to avoid this pattern or add a maxsize to the cache. The default value for maxsize is 128.

Problematic code:

import functools
class Fibonnaci:
    def __init__(self):
        self.result = []
    @functools.lru_cache(maxsize=None)  # [method-cache-max-size-none]
    def fibonacci(self, n):
        if n in {0, 1}:
            self.result.append(n)
        self.result.append(self.fibonacci(n - 1) + self.fibonacci(n - 2))

Correct code:

import functools
@functools.cache
def cached_fibonacci(n):
    if n in {0, 1}:
        return n
    return cached_fibonacci(n - 1) + cached_fibonacci(n - 2)
class Fibonnaci:
    def __init__(self):
        self.result = []
    def fibonacci(self, n):
        self.result.append(cached_fibonacci(n))

Created by the stdlib checker.

  misplaced-future / W0410

Message emitted:

__future__ import is not the first non docstring statement

Description:

Python 2.5 and greater require __future__ import to be the first non docstring statement in the module.

Problematic code:

import sys
from __future__ import print_function  # [misplaced-future]

Correct code:

from __future__ import print_function
import sys

Additional details:

A bare raise statement will re-raise the last active exception in the current scope. If the raise statement is not in an except or finally block, a RuntimeError will be raised instead.

Created by the imports checker.

  missing-any-param-doc / W9021

Message emitted:

Missing any documentation in "%s"

Description:

Please add parameter and/or type documentation.

Problematic code:

def puppies(head, tail): #[missing-any-param-doc]
    """Print puppy's details."""
    print(head, tail)

Correct code:

def puppies(head: str, tail: str):
    """Print puppy's details.
        :param head: description of the head of the dog
        :param tail: description of the tail of the dog
    """
    print(head, tail)

Configuration file:

[main]
load-plugins = pylint.extensions.docparams
accept-no-param-doc = false

NOTE:

This message is emitted by the optional 'parameter_documentation'
    checker which requires the pylint.extensions.docparams plugin to be loaded.

    Created by the parameter_documentation checker.

  missing-format-argument-key / W1303

Message emitted:

Missing keyword argument %r for format string

Description:

Used when a PEP 3101 format string that uses named fields doesn't receive one or more required keywords.

Problematic code:

print("My name is {first} {last}".format(first="John"))  # [missing-format-argument-key]

Correct code:

print("My name is {first} {last}".format(first="John", last="Wick"))

Related links:

•   PEP 3101

•   Custom String Formmating

    Created by the string checker.

  missing-format-attribute / W1306

Message emitted:

Missing format attribute %r in format specifier %r

Description:

Used when a PEP 3101 format string uses an attribute specifier ({0.length}), but the argument passed for formatting doesn't have that attribute.

Problematic code:

print("{0.real}".format("1"))  # [missing-format-attribute]

Correct code:

print("{0.real}".format(1))

Created by the string checker.

  missing-param-doc / W9015

Message emitted:

"%s" missing in parameter documentation

Description:

Please add parameter declarations for all parameters.

Problematic code:

def integer_sum(a: int, b):  # [missing-param-doc]
    """Returns sum of two integers
    :param a: first integer
    """
    return a + b

Correct code:

def integer_sum(a: int, b: int):
    """Returns sum of two integers
    :param a: first integer
    :param b: second integer
    """
    return a + b

Configuration file:

[MAIN]
load-plugins = pylint.extensions.docparams

NOTE:

This message is emitted by the optional 'parameter_documentation'
    checker which requires the pylint.extensions.docparams plugin to be loaded.

    Created by the parameter_documentation checker.

  missing-parentheses-for-call-in-test / W0126

Message emitted:

Using a conditional statement with potentially wrong function or method call due to missing parentheses

Description:

Emitted when a conditional statement (If or ternary if) seems to wrongly call a function due to missing parentheses

Problematic code:

import random
def is_it_a_good_day():
    return random.choice([True, False])
if is_it_a_good_day:  # [missing-parentheses-for-call-in-test]
    print("Today is a good day!")

Correct code:

import random
def is_it_a_good_day():
    return random.choice([True, False])
if is_it_a_good_day():
    print("Today is a good day!")

Created by the basic checker.

  missing-raises-doc / W9006

Message emitted:

"%s" not documented as being raised

Description:

Please document exceptions for all raised exception types.

Problematic code:

def integer_sum(a: int, b: int):  # [missing-raises-doc]
    """Returns sum of two integers
    :param a: first integer
    :param b: second integer
    """
    if not (isinstance(a, int) and isinstance(b, int)):
        raise ValueError('Function supports only integer parameters.')
    return a + b

Correct code:

def integer_sum(a: int, b: int):
    """Returns sum of two integers
    :param a: first integer
    :param b: second integer
    :raises ValueError: One of the parameters is not an integer.
    """
    if not (isinstance(a, int) and isinstance(b, int)):
        raise ValueError('Function supports only integer parameters.')
    return a + b

Configuration file:

[MAIN]
load-plugins = pylint.extensions.docparams
[BASIC]
accept-no-raise-doc = no

NOTE:

This message is emitted by the optional 'parameter_documentation'
    checker which requires the pylint.extensions.docparams plugin to be loaded.

    Created by the parameter_documentation checker.

  missing-return-doc / W9011

Message emitted:

Missing return documentation

Description:

Please add documentation about what this method returns.

Problematic code:

def integer_sum(a: int, b: int):  # [missing-return-doc]
    """Returns sum of two integers
    :param a: first integer
    :param b: second integer
    """
    return a + b

Correct code:

def integer_sum(a: int, b: int) -> int:
    """Returns sum of two integers
    :param a: first integer
    :param b: second integer
    :return: sum of parameters a and b
    """
    return a + b

Configuration file:

[main]
load-plugins=pylint.extensions.docparams
[Parameter_documentation]
accept-no-return-doc=no

Additional details:

This message is raised only when parameter accept-no-return-doc is set to no.

NOTE:

This message is emitted by the optional 'parameter_documentation'
    checker which requires the pylint.extensions.docparams plugin to be loaded.

    Created by the parameter_documentation checker.

  missing-return-type-doc / W9012

Message emitted:

Missing return type documentation

Description:

Please document the type returned by this method.

Problematic code:

def integer_sum(a: int, b: int):  # [missing-return-type-doc]
    """Returns sum of two integers
    :param a: first integer
    :param b: second integer
    :return: sum of parameters a and b
    """
    return a + b

Correct code:

def integer_sum(a: int, b: int) -> int:
    """Returns sum of two integers
    :param a: first integer
    :param b: second integer
    :return: sum of parameters a and b
    """
    return a + b

Configuration file:

[main]
load-plugins=pylint.extensions.docparams
[Parameter_documentation]
accept-no-return-doc=no

Additional details:

This message is raised only when parameter accept-no-return-doc is set to no.

NOTE:

This message is emitted by the optional 'parameter_documentation'
    checker which requires the pylint.extensions.docparams plugin to be loaded.

    Created by the parameter_documentation checker.

  missing-timeout / W3101

Message emitted:

Missing timeout argument for method '%s' can cause your program to hang indefinitely

Description:

Used when a method needs a 'timeout' parameter in order to avoid waiting for a long time. If no timeout is specified explicitly the default value is used. For example for 'requests' the program will never time out (i.e. hang indefinitely).

Problematic code:

import requests
requests.post("http://localhost")  # [missing-timeout]

Correct code:

import requests
requests.post("http://localhost", timeout=10)

Additional details:

You can add new methods that should have a defined `timeout argument as qualified names in the timeout-methods option, for example:

•   requests.api.get

•   requests.api.head

•   requests.api.options

•   requests.api.patch

•   requests.api.post

•   requests.api.put

•   requests.api.request

    Created by the method_args checker.

  missing-type-doc / W9016

Message emitted:

"%s" missing in parameter type documentation

Description:

Please add parameter type declarations for all parameters.

Problematic code:

def integer_sum(a: int, b):  # [missing-type-doc]
    """Returns sum of two integers
    :param a: first integer
    :param b: second integer
    """
    return a + b

Correct code:

def integer_sum(a: int, b: int):
    """Returns sum of two integers
    :param a: first integer
    :param b: second integer
    """
    return a + b

Configuration file:

[MAIN]
load-plugins = pylint.extensions.docparams

NOTE:

This message is emitted by the optional 'parameter_documentation'
    checker which requires the pylint.extensions.docparams plugin to be loaded.

    Created by the parameter_documentation checker.

  missing-yield-doc / W9013

Message emitted:

Missing yield documentation

Description:

Please add documentation about what this generator yields.

Problematic code:

def even_number_under(n: int):  # [missing-yield-doc]
    """Prints even numbers smaller than n.
    Args:
        n: Upper limit of even numbers.
    """
    for i in range(n):
        if i % 2 == 1:
            continue
        yield i

Correct code:

from typing import Iterator
def even_number_under(n: int) -> Iterator[int]:
    """Prints even numbers smaller than n.
    Args:
        n: Upper limit of even numbers.
    Yields:
        even numbers
    """
    for i in range(n):
        if i % 2 == 1:
            continue
        yield i

Configuration file:

[main]
load-plugins=pylint.extensions.docparams
[Parameter_documentation]
accept-no-yields-doc=no

Additional details:

This message is raised only when parameter accept-no-yields-doc is set to no.

NOTE:

This message is emitted by the optional 'parameter_documentation'
    checker which requires the pylint.extensions.docparams plugin to be loaded.

    Created by the parameter_documentation checker.

  missing-yield-type-doc / W9014

Message emitted:

Missing yield type documentation

Description:

Please document the type yielded by this method.

Problematic code:

def even_number_under(n: int):  # [missing-yield-type-doc]
    """Prints even numbers smaller than n.
    Args:
        n: Upper limit of even numbers.
    Yields:
        even numbers
    """
    for i in range(n):
        if i % 2 == 1:
            continue
        yield i

Correct code:

from typing import Iterator
def even_number_under(n: int) -> Iterator[int]:
    """Prints even numbers smaller than n.
    Args:
        n: Upper limit of even numbers.
    Yields:
        even numbers
    """
    for i in range(n):
        if i % 2 == 1:
            continue
        yield i

Configuration file:

[main]
load-plugins=pylint.extensions.docparams
[Parameter_documentation]
accept-no-yields-doc=no

Additional details:

This message is raised only when parameter accept-no-yields-doc is set to no.

NOTE:

This message is emitted by the optional 'parameter_documentation'
    checker which requires the pylint.extensions.docparams plugin to be loaded.

    Created by the parameter_documentation checker.

  modified-iterating-list / W4701

Message emitted:

Iterated list '%s' is being modified inside for loop body, consider iterating through a copy of it instead.

Description:

Emitted when items are added or removed to a list being iterated through. Doing so can result in unexpected behaviour, that is why it is preferred to use a copy of the list.

Problematic code:

fruits = ["apple", "orange", "mango"]
for fruit in fruits:
    fruits.append("pineapple")  # [modified-iterating-list]

Correct code:

fruits = ["apple", "orange", "mango"]
for fruit in fruits.copy():
    fruits.append("pineapple")

Created by the modified_iteration checker.

  multiple-constructor-doc / W9005

Message emitted:

"%s" has constructor parameters documented in class and __init__

Description:

Please remove parameter declarations in the class or constructor.

Problematic code:

class Point:  # [multiple-constructor-doc]
    """Represents a point in the xy-coordinate plane.
    :param x: coordinate
    :param y: coordinate
    """
    def __init__(self, x, y):
        """Represents a point in the xy-coordinate plane.
        :param x: coordinate
        :param y: coordinate
        """
        self.x = x
        self.y = y

Correct code:

class Point:
    def __init__(self, x, y):
        """Represents a point in the xy-coordinate plane.
        :param x: x coordinate
        :param y: y coordinate
        """
        self.x = x
        self.y = y

Configuration file:

[main]
load-plugins=pylint.extensions.docparams
[Parameter_documentation]
no-docstring-rgx=^(?!__init__$)_

Additional details:

Both docstrings are acceptable but not both at the same time.

NOTE:

This message is emitted by the optional 'parameter_documentation'
    checker which requires the pylint.extensions.docparams plugin to be loaded.

    Created by the parameter_documentation checker.

  named-expr-without-context / W0131

Message emitted:

Named expression used without context

Description:

Emitted if named expression is used to do a regular assignment outside a context like if, for, while, or a comprehension.

Problematic code:

(a := 42)  # [named-expr-without-context]

Correct code:

if (a := 42):
    print('Success')

Created by the basic checker.

  nan-comparison / W0177

Message emitted:

Comparison %s should be %s

Description:

Used when an expression is compared to NaN values like numpy.NaN and float('nan').

Problematic code:

import numpy as np
def both_nan(x, y) -> bool:
    return x == np.NaN and y == float("nan")  # [nan-comparison, nan-comparison]

Correct code:

import numpy as np
def both_nan(x, y) -> bool:
    return np.isnan(x) and np.isnan(y)

Created by the basic checker.

  nested-min-max / W3301

Message emitted:

Do not use nested call of '%s'; it's possible to do '%s' instead

Description:

Nested calls ``min(1, min(2, 3))`` can be rewritten as ``min(1, 2, 3)``.

Problematic code:

print(min(1, min(2, 3)))  # [nested-min-max]

Correct code:

print(min(1, 2, 3))

Created by the nested_min_max checker.

  non-ascii-file-name / W2402

Message emitted:

%s name "%s" contains a non-ASCII character.

Description:

Under python 3.5, PEP 3131 allows non-ascii identifiers, but not non-ascii file names.Since Python 3.5, even though Python supports UTF-8 files, some editors or tools don't.

Problematic code:

bàd.py:

# [non-ascii-file-name]

not_bétter.py:

# [non-ascii-file-name]

Correct code:

bad.py:

not_better.py:

Related links:

•   PEP 489

•   PEP 672

•   Python issue 20485

    Created by the nonascii-checker checker.

  non-parent-init-called / W0233

Message emitted:

__init__ method from a non direct base class %r is called

Description:

Used when an __init__ method is called on a class which is not in the direct ancestors for the analysed class.

Problematic code:

class Animal:
    def __init__(self):
        self.is_multicellular = True
class Vertebrate(Animal):
    def __init__(self):
        super().__init__()
        self.has_vertebrae = True
class Cat(Vertebrate):
    def __init__(self):
        Animal.__init__(self)  # [non-parent-init-called]
        self.is_adorable = True

Correct code:

class Animal:
    def __init__(self):
        self.is_multicellular = True
class Vertebrate(Animal):
    def __init__(self):
        super().__init__()
        self.has_vertebrae = True
class Cat(Vertebrate):
    def __init__(self):
        super().__init__()
        self.is_adorable = True

Created by the classes checker.

  non-str-assignment-to-dunder-name / W1115

Message emitted:

Non-string value assigned to __name__

Description:

Emitted when a non-string value is assigned to __name__

Problematic code:

class Fruit:
    pass
Fruit.__name__ = 1  # [non-str-assignment-to-dunder-name]

Correct code:

class Fruit:
    pass
Fruit.__name__ = "FRUIT"

Created by the typecheck checker.

  overlapping-except / W0714

Message emitted:

Overlapping exceptions (%s)

Description:

Used when exceptions in handler overlap or are identical

Problematic code:

def divide_x_by_y(x: float, y: float):
    try:
        print(x / y)
    except (ArithmeticError, FloatingPointError) as e:  # [overlapping-except]
        print(f"There was an issue: {e}")

Correct code:

def divide_x_by_y(x: float, y: float):
    try:
        print(x / y)
    except FloatingPointError as e:
        print(f"There was a FloatingPointError: {e}")
    except ArithmeticError as e:
        # FloatingPointError  were already caught at this point
        print(f"There was an OverflowError or a ZeroDivisionError: {e}")
# Or:
def divide_x_by_y(x: float, y: float):
    try:
        print(x / y)
    except ArithmeticError as e:
        print(f"There was an OverflowError, a ZeroDivisionError or a FloatingPointError: {e}")

Configuration file:

[MAIN]
load-plugins=pylint.extensions.overlapping_exceptions,

Related links:

•   Exception hierarchy

    NOTE:

This message is emitted by the optional 'overlap-except'
    checker which requires the pylint.extensions.overlapping_exceptions plugin to be loaded.

    Created by the overlap-except checker.

  overridden-final-method / W0239

Message emitted:

Method %r overrides a method decorated with typing.final which is defined in class %r

Description:

Used when a method decorated with typing.final has been overridden.

Problematic code:

from typing import final
class Animal:
    @final
    def can_breathe(self):
        return True
class Cat(Animal):
    def can_breathe(self):  # [overridden-final-method]
        pass

Correct code:

from typing import final
class Animal:
    @final
    def can_breathe(self):
        return True
class Cat(Animal):
    def can_purr(self):
        return True

Configuration file:

[MAIN]
py-version=3.8

Additional details:

The message can't be emitted when using Python < 3.8.

Related links:

•   PEP 591

    Created by the classes checker.

  pointless-exception-statement / W0133

Message emitted:

Exception statement has no effect

Description:

Used when an exception is created without being assigned, raised or returned for subsequent use elsewhere.

Problematic code:

Exception("This exception is a statement.")  # [pointless-exception-statement]

Correct code:

raise Exception("This will raise.")

Created by the basic checker.

  pointless-statement / W0104

Message emitted:

Statement seems to have no effect

Description:

Used when a statement doesn't have (or at least seems to) any effect.

Problematic code:

[1, 2, 3]  # [pointless-statement]

Correct code:

NUMBERS = [1, 2, 3]
print(NUMBERS)

Created by the basic checker.

  pointless-string-statement / W0105

Message emitted:

String statement has no effect

Description:

Used when a string is used as a statement (which of course has no effect). This is a particular case of W0104 with its own message so you can easily disable it if you're using those strings as documentation, instead of comments.

Problematic code:

"""This is a docstring which describes the module"""
"""This is not a docstring"""  # [pointless-string-statement]

Correct code:

"""This is a docstring which describes the module"""
# This is comment which describes a particular part of the module.

Created by the basic checker.

  possibly-unused-variable / W0641

Message emitted:

Possibly unused variable %r

Description:

Used when a variable is defined but might not be used. The possibility comes from the fact that locals() might be used, which could consume or not the said variable

Problematic code:

def choose_fruits(fruits):
    print(fruits)
    color = "red"  # [possibly-unused-variable]
    return locals()

Correct code:

def choose_fruits(fruits):
    current_locals = locals()
    print(fruits)
    color = "red"
    print(color)
    return current_locals

Created by the variables checker.

  preferred-module / W0407

Message emitted:

Prefer importing %r instead of %r

Description:

Used when a module imported has a preferred replacement module.

Problematic code:

import urllib  # [preferred-module]

Correct code:

import requests

Configuration file:

[IMPORTS]
preferred-modules=urllib:requests,

Created by the imports checker.

  protected-access / W0212

Message emitted:

Access to a protected member %s of a client class

Description:

Used when a protected member (i.e. class member with a name beginning with an underscore) is access outside the class or a descendant of the class where it's defined.

Problematic code:

class Worm:
    def __swallow(self):
        pass
jim = Worm()
jim.__swallow()  # [protected-access]

Correct code:

class Worm:
    def __swallow(self):
        pass
    def eat(self):
        return self.__swallow()
jim = Worm()
jim.eat()

Created by the classes checker.

  raise-missing-from / W0707

Message emitted:

Consider explicitly re-raising using %s'%s from %s'

Description:

Python's exception chaining shows the traceback of the current exception, but also of the original exception. When you raise a new exception after another exception was caught it's likely that the second exception is a friendly re-wrapping of the first exception. In such cases `raise from` provides a better link between the two tracebacks in the final error.

Problematic code:

try:
    1 / 0
except ZeroDivisionError as e:
    raise ValueError("Rectangle Area cannot be zero")  # [raise-missing-from]

Correct code:

try:
    1 / 0
except ZeroDivisionError as e:
    raise ValueError("Rectangle Area cannot be zero") from e

Related links:

•   PEP 3134

    Created by the exceptions checker.

  raising-format-tuple / W0715

Message emitted:

Exception arguments suggest string formatting might be intended

Description:

Used when passing multiple arguments to an exception constructor, the first of them a string literal containing what appears to be placeholders intended for formatting

Problematic code:

raise RuntimeError("This looks wrong %s %s", ("a", "b"))  # [raising-format-tuple]

Correct code:

raise RuntimeError("This looks wrong %s %s" % ("a", "b"))

Created by the exceptions checker.

  redeclared-assigned-name / W0128

Message emitted:

Redeclared variable %r in assignment

Description:

Emitted when we detect that a variable was redeclared in the same assignment.

Problematic code:

FIRST, FIRST = (1, 2)  # [redeclared-assigned-name]

Correct code:

FIRST, SECOND = (1, 2)

Created by the basic checker.

  redefined-builtin / W0622

Message emitted:

Redefining built-in %r

Description:

Used when a variable or function override a built-in.

Problematic code:

def map():  # [redefined-builtin]
    pass

Correct code:

def map_iterable():
    pass

Created by the variables checker.

  redefined-loop-name / W2901

Message emitted:

Redefining %r from loop (line %s)

Description:

Used when a loop variable is overwritten in the loop body.

Problematic code:

for name in names:
    name = name.lower()  # [redefined-loop-name]

Correct code:

for name in names:
    lowercased_name = name.lower()

Configuration file:

[MAIN]
load-plugins=pylint.extensions.redefined_loop_name,

NOTE:

This message is emitted by the optional 'redefined-loop-name'
    checker which requires the pylint.extensions.redefined_loop_name plugin to be loaded.

    Created by the redefined-loop-name checker.

  redefined-outer-name / W0621

Message emitted:

Redefining name %r from outer scope (line %s)

Description:

Used when a variable's name hides a name defined in an outer scope or except handler.

Problematic code:

count = 10
def count_it(count):  # [redefined-outer-name]
    for i in range(count):
        print(i)

Correct code:

count = 10
def count_it(limit):
    for i in range(limit):
        print(i)

Additional details:

A common issue is that this message is triggered when using pytest fixtures:

import pytest
@pytest.fixture
def setup():
    ...
def test_something(setup):  # [redefined-outer-name]
    ...

One solution to this problem is to explicitly name the fixture:

@pytest.fixture(name="setup")
def setup_fixture():
    ...

Alternatively pylint plugins like pylint-pytest can be used.

Created by the variables checker.

  redefined-slots-in-subclass / W0244

Message emitted:

Redefined slots %r in subclass

Description:

Used when a slot is re-defined in a subclass.

Problematic code:

class Base:
    __slots__ = ("a", "b")
class Subclass(Base):
    __slots__ = ("a", "d")  # [redefined-slots-in-subclass]

Correct code:

class Base:
    __slots__ = ("a", "b")
class Subclass(Base):
    __slots__ = ("d",)

Created by the classes checker.

  redundant-returns-doc / W9008

Message emitted:

Redundant returns documentation

Description:

Please remove the return/rtype documentation from this method.

Problematic code:

def print_fruits(fruits):  # [redundant-returns-doc]
    """Print list of fruits
    Returns
    -------
        str
    """
    print(fruits)
    return None

Correct code:

def print_fruits(fruits):
    """Print list of fruits
    Returns
    -------
        str
    """
    print(fruits)
    return ",".join(fruits)

Configuration file:

[MAIN]
load-plugins = pylint.extensions.docparams

NOTE:

This message is emitted by the optional 'parameter_documentation'
    checker which requires the pylint.extensions.docparams plugin to be loaded.

    Created by the parameter_documentation checker.

  redundant-u-string-prefix / W1406

Message emitted:

The u prefix for strings is no longer necessary in Python >=3.0

Description:

Used when we detect a string with a u prefix. These prefixes were necessary in Python 2 to indicate a string was Unicode, but since Python 3.0 strings are Unicode by default.

Problematic code:

def print_fruit():
    print(u"Apple")  # [redundant-u-string-prefix]

Correct code:

def print_fruit():
    print("Apple")

Created by the string checker.

  redundant-unittest-assert / W1503

Message emitted:

Redundant use of %s with constant value %r

Description:

The first argument of assertTrue and assertFalse is a condition. If a constant is passed as parameter, that condition will be always true. In this case a warning should be emitted.

Problematic code:

import unittest
class DummyTestCase(unittest.TestCase):
    def test_dummy(self):
        self.assertTrue("foo")  # [redundant-unittest-assert]

Correct code:

import unittest
class DummyTestCase(unittest.TestCase):
    def test_dummy(self):
        actual = "test_result"
        self.assertEqual(actual, "expected")

Additional details:

Directly asserting a string literal will always pass. The solution is to test something that could fail, or not assert at all.

For assertions using assert there are similar messages: assert-on-string-literal / W0129 and assert-on-tuple / W0199.

Related links:

•   Tests without assertion

•   Testing that there is no error raised

•   Parametrizing conditional raising

    Created by the stdlib checker.

  redundant-yields-doc / W9010

Message emitted:

Redundant yields documentation

Description:

Please remove the yields documentation from this method.

Problematic code:

def give_fruits(fruits):  # [redundant-yields-doc]
    """Something about fruits
    Yields
    -------
        list
            fruits
    """
    return fruits

Correct code:

def give_fruits(fruits):
    """Something about fruits
    Yields
    -------
        str
            fruit
    """
    for fruit in fruits:
        yield fruit

Configuration file:

[MAIN]
load-plugins = pylint.extensions.docparams

NOTE:

This message is emitted by the optional 'parameter_documentation'
    checker which requires the pylint.extensions.docparams plugin to be loaded.

    Created by the parameter_documentation checker.

  reimported / W0404

Message emitted:

Reimport %r (imported line %s)

Description:

Used when a module is imported more than once.

Problematic code:

import re
import re  # [reimported]

Correct code:

import re

Created by the imports checker.

  self-assigning-variable / W0127

Message emitted:

Assigning the same variable %r to itself

Description:

Emitted when we detect that a variable is assigned to itself

Problematic code:

year = 2000
year = year  # [self-assigning-variable]

Correct code:

year = 2000

Related links:

•   Python assignment statement

    Created by the basic checker.

  self-cls-assignment / W0642

Message emitted:

Invalid assignment to %s in method

Description:

Invalid assignment to self or cls in instance or class method respectively.

Problematic code:

class Fruit:
    @classmethod
    def list_fruits(cls):
        cls = 'apple'  # [self-cls-assignment]
    def print_color(self, *colors):
        self = "red"  # [self-cls-assignment]
        color = colors[1]
        print(color)

Correct code:

class Fruit:
    @classmethod
    def list_fruits(cls):
        fruit = 'apple'
        print(fruit)
    def print_color(self, *colors):
        color = colors[1]
        print(color)

Created by the variables checker.

  shadowed-import / W0416

Message emitted:

Shadowed %r (imported line %s)

Description:

Used when a module is aliased with a name that shadows another import.

Problematic code:

from pathlib import Path
import FastAPI.Path as Path  # [shadowed-import]

Correct code:

from pathlib import Path
import FastAPI.Path as FastApiPath

Created by the imports checker.

  shallow-copy-environ / W1507

Message emitted:

Using copy.copy(os.environ). Use os.environ.copy() instead.

Description:

os.environ is not a dict object but proxy object, so shallow copy has still effects on original object. See https://bugs.python.org/issue15373 for reference.

Problematic code:

import copy
import os
copied_env = copy.copy(os.environ)  # [shallow-copy-environ]

Correct code:

import os
copied_env = os.environ.copy()

Created by the stdlib checker.

  signature-differs / W0222

Message emitted:

Signature differs from %s %r method

Description:

Used when a method signature is different than in the implemented interface or in an overridden method.

Problematic code:

class Animal:
    def run(self, distance=0):
        print(f"Ran {distance} km!")
class Dog(Animal):
    def run(self, distance):  # [signature-differs]
        super(Animal, self).run(distance)
        print("Fetched that stick, wuff !")

Correct code:

class Animal:
    def run(self, distance=0):
        print(f"Ran {distance} km!")
class Dog(Animal):
    def run(self, distance=0):
        super(Animal, self).run(distance)
        print("Fetched that stick, wuff !")

Created by the classes checker.

  subclassed-final-class / W0240

Message emitted:

Class %r is a subclass of a class decorated with typing.final: %r

Description:

Used when a class decorated with typing.final has been subclassed.

Problematic code:

from typing import final
@final
class PlatypusData:
    """General Platypus data."""
    average_length = 46
    average_body_temperature = 32
class FluorescentPlaytipus(PlatypusData):  # [subclassed-final-class]
    """Playtipus with fluorescent fur."""

Correct code:

from typing import final
@final
class PlatypusData:
    """General Platypus data."""
    average_length = 46
    average_body_temperature = 32
def print_average_length_platypus():
    output = f"The average length of a platypus is: {PlatypusData.average_length}cm"
    print(output)

Configuration file:

[MAIN]
py-version=3.8

Additional details:

This message is emitted when a class which is decorated with final is subclassed; the decorator indicates that the class is not intended to be extended.

Note this message can't be emitted when using Python < 3.8.

Related links:

•   PEP 591

    Created by the classes checker.

  subprocess-popen-preexec-fn / W1509

Message emitted:

Using preexec_fn keyword which may be unsafe in the presence of threads

Description:

The preexec_fn parameter is not safe to use in the presence of threads in your application. The child process could deadlock before exec is called. If you must use it, keep it trivial! Minimize the number of libraries you call into. See https://docs.python.org/3/library/subprocess.html#popen-constructor

Problematic code:

import subprocess
def foo():
    pass
subprocess.Popen(preexec_fn=foo) # [subprocess-popen-preexec-fn]

Correct code:

import subprocess
subprocess.Popen()

Created by the stdlib checker.

  subprocess-run-check / W1510

Message emitted:

'subprocess.run' used without explicitly defining the value for 'check'.

Description:

The ``check`` keyword is set to False by default. It means the process launched by ``subprocess.run`` can exit with a non-zero exit code and fail silently. It's better to set it explicitly to make clear what the error-handling behavior is.

Problematic code:

import subprocess
proc = subprocess.run(["ls"])  # [subprocess-run-check]

Correct code:

import subprocess
proc = subprocess.run(["ls"], check=False)

Related links:

•   subprocess.run documentation

    Created by the stdlib checker.

  super-init-not-called / W0231

Message emitted:

__init__ method from base class %r is not called

Description:

Used when an ancestor class method has an __init__ method which is not called by a derived class.

Problematic code:

class Fruit:
    def __init__(self, name="fruit"):
        self.name = name
        print("Creating a {self.name}")
class Apple(Fruit):
    def __init__(self):  # [super-init-not-called]
        print("Creating an apple")

Correct code:

class Fruit:
    def __init__(self, name="fruit"):
        self.name = name
        print("Creating a {self.name}")
class Apple(Fruit):
    def __init__(self):
        super().__init__("apple")

Created by the classes checker.

  super-without-brackets / W0245

Message emitted:

Super call without brackets

Description:

Used when a call to super does not have brackets and thus is not an actual call and does not work as expected.

Problematic code:

class Soup:
    @staticmethod
    def temp():
        print("Soup is hot!")
class TomatoSoup(Soup):
    @staticmethod
    def temp():
        super.temp()  # [super-without-brackets]
        print("But tomato soup is even hotter!")

Correct code:

class Soup:
    @staticmethod
    def temp():
        print("Soup is hot!")
class TomatoSoup(Soup):
    @staticmethod
    def temp():
        super().temp()
        print("But tomato soup is even hotter!")

Created by the classes checker.

  too-many-try-statements / W0717

Message emitted:

%s

Description:

Try clause contains too many statements.

Problematic code:

FRUITS = {"apple": 1, "orange": 10}
def pick_fruit(name):
    try:  # [too-many-try-statements]
        count = FRUITS[name]
        count += 1
        print(f"Got fruit count {count}")
    except KeyError:
        return

Correct code:

FRUITS = {"apple": 1, "orange": 10}
def pick_fruit(name):
    try:
        count = FRUITS[name]
    except KeyError:
        return
    count += 1
    print(f"Got fruit count {count}")

Configuration file:

[MAIN]
load-plugins=pylint.extensions.broad_try_clause,

NOTE:

This message is emitted by the optional 'broad_try_clause'
    checker which requires the pylint.extensions.broad_try_clause plugin to be loaded.

    Created by the broad_try_clause checker.

  try-except-raise / W0706

Message emitted:

The except handler raises immediately

Description:

Used when an except handler uses raise as its first or only operator. This is useless because it raises back the exception immediately. Remove the raise operator or the entire try-except-raise block!

Problematic code:

try:
    1 / 0
except ZeroDivisionError as e:  # [try-except-raise]
    raise

Correct code:

# The try except might be removed entirely:
1 / 0
# Or another more detailed exception can be raised:
try:
    1 / 0
except ZeroDivisionError as e:
    raise ValueError("The area of the rectangle cannot be zero") from e

Additional details:

There is a legitimate use case for re-raising immediately. E.g. with the following inheritance tree:

+-- ArithmeticError
     +-- FloatingPointError
     +-- OverflowError
     +-- ZeroDivisionError

The following code shows valid case for re-raising exception immediately:

def execute_calculation(a, b):
    try:
        return some_calculation(a, b)
    except ZeroDivisionError:
        raise
    except ArithmeticError:
        return float('nan')

The pylint is able to detect this case and does not produce error.

Created by the exceptions checker.

  unbalanced-dict-unpacking / W0644

Message emitted:

Possible unbalanced dict unpacking with %s: left side has %d label%s, right side has %d value%s

Description:

Used when there is an unbalanced dict unpacking in assignment or for loop

Problematic code:

FRUITS = {"apple": 2, "orange": 3, "mellon": 10}
for fruit, price in FRUITS.values():  # [unbalanced-dict-unpacking]
    print(fruit)

Correct code:

FRUITS = {"apple": 2, "orange": 3, "mellon": 10}
for fruit, price in FRUITS.items():
    print(fruit)

Created by the variables checker.

  undefined-loop-variable / W0631

Message emitted:

Using possibly undefined loop variable %r

Description:

Used when a loop variable (i.e. defined by a for loop or a list comprehension or a generator expression) is used outside the loop.

Problematic code:

def find_even_number(numbers):
    for x in numbers:
        if x % 2 == 0:
            break
    return x  # [undefined-loop-variable]

Correct code:

def find_even_number(numbers):
    for x in numbers:
        if x % 2:
            return x
    return None

Created by the variables checker.

  unnecessary-ellipsis / W2301

Message emitted:

Unnecessary ellipsis constant

Description:

Used when the ellipsis constant is encountered and can be avoided. A line of code consisting of an ellipsis is unnecessary if there is a docstring on the preceding line or if there is a statement in the same scope.

Problematic code:

def my_function():
    """My docstring"""
    ...  # [unnecessary-ellipsis]

Correct code:

def my_function():
    """My docstring"""

Created by the unnecessary_ellipsis checker.

  unnecessary-lambda / W0108

Message emitted:

Lambda may not be necessary

Description:

Used when the body of a lambda expression is a function call on the same argument list as the lambda itself; such lambda expressions are in all but a few cases replaceable with the function being called in the body of the lambda.

Problematic code:

function = lambda x: print(x)  # [unnecessary-lambda]
function("Hello world !")
df.apply(lambda x: str(x))  # [unnecessary-lambda]

Correct code:

print("Hello world !")
df.apply(str)

Created by the basic checker.

  unnecessary-pass / W0107

Message emitted:

Unnecessary pass statement

Description:

Used when a "pass" statement that can be avoided is encountered.

Problematic code:

class Foo:
    """Foo docstring."""
    pass  # [unnecessary-pass]

Correct code:

class Foo:
    """Foo docstring."""

Created by the basic checker.

  unnecessary-semicolon / W0301

Message emitted:

Unnecessary semicolon

Description:

Used when a statement is ended by a semi-colon (";"), which isn't necessary (that's python, not C ;).

Problematic code:

print("Hello World!");  # [unnecessary-semicolon]

Correct code:

print("Hello World!")

Created by the format checker.

  unreachable / W0101

Message emitted:

Unreachable code

Description:

Used when there is some code behind a "return" or "raise" statement, which will never be accessed.

Problematic code:

def say_hello():
    return True
    print("Hello World!, Outside function.")  # [unreachable]

Correct code:

def say_hello():
    print("Hello World!, Inside function.")
    return True

Created by the basic checker.

  unspecified-encoding / W1514

Message emitted:

Using open without explicitly specifying an encoding

Description:

It is better to specify an encoding when opening documents. Using the system default implicitly can create problems on other operating systems. See https://peps.python.org/pep-0597/

Problematic code:

def foo(file_path):
    with open(file_path) as file:  # [unspecified-encoding]
        contents = file.read()

Correct code:

def foo(file_path):
    with open(file_path, encoding="utf-8") as file:
        contents = file.read()

Created by the stdlib checker.

  unused-argument / W0613

Message emitted:

Unused argument %r

Description:

Used when a function or method argument is not used.

Problematic code:

def print_point(x, y):  # [unused-argument]
    print(f"Point is located at {x},{x}")

Correct code:

def print_point(x, y):
    print(f"Point is located at {x},{y}")

Created by the variables checker.

  unused-format-string-argument / W1304

Message emitted:

Unused format argument %r

Description:

Used when a PEP 3101 format string that uses named fields is used with an argument that is not required by the format string.

Problematic code:

print("{x} {y}".format(x=1, y=2, z=3))  # [unused-format-string-argument]

Correct code:

print("{x} {y} {z}".format(x=1, y=2, z=3))
# or
print("{x} {y}".format(x=1, y=2))

Created by the string checker.

  unused-format-string-key / W1301

Message emitted:

Unused key %r in format string dictionary

Description:

Used when a format string that uses named conversion specifiers is used with a dictionary that contains keys not required by the format string.

Problematic code:

"The quick %(color)s fox jumps over the lazy dog." % {"color": "brown", "action": "hops"}
# -1: [unused-format-string-key]

Correct code:

"The quick %(color)s fox %(action)s over the lazy dog." % {"color": "brown", "action": "hops"}

Created by the string checker.

  unused-import / W0611

Message emitted:

Unused %s

Description:

Used when an imported module or variable is not used.

Problematic code:

from logging import getLogger
from pathlib import Path  # [unused-import]
LOGGER = getLogger(__name__)

Correct code:

from logging import getLogger
LOGGER = getLogger(__name__)

Created by the variables checker.

  unused-private-member / W0238

Message emitted:

Unused private member `%s.%s`

Description:

Emitted when a private member of a class is defined but not used.

Problematic code:

class Fruit:
    FRUITS = {"apple": "red", "orange": "orange"}
    def __print_color(self):  # [unused-private-member]
        pass

Correct code:

class Fruit:
    FRUITS = {"apple": "red", "orange": "orange"}
    def __print_color(self, name, color):
        print(f"{name}: {color}")
    def print(self):
        for fruit, color in self.FRUITS.items():
            self.__print_color(fruit, color)

Created by the classes checker.

  unused-variable / W0612

Message emitted:

Unused variable %r

Description:

Used when a variable is defined but not used.

Problematic code:

def print_fruits():
    fruit1 = "orange"
    fruit2 = "apple"  # [unused-variable]
    print(fruit1)

Correct code:

def print_fruits():
    fruit1 = "orange"
    fruit2 = "apple"
    print(fruit1, fruit2)

Created by the variables checker.

  unused-wildcard-import / W0614

Message emitted:

Unused import(s) %s from wildcard import of %s

Description:

Used when an imported module or variable is not used from a `'from X import *'` style import.

Problematic code:

from abc import *  # [unused-wildcard-import]
class Animal(ABC): ...

Correct code:

from abc import ABC
class Animal(ABC): ...

Created by the variables checker.

  useless-else-on-loop / W0120

Message emitted:

Else clause on loop without a break statement, remove the else and de-indent all the code inside it

Description:

Loops should only have an else clause if they can exit early with a break statement, otherwise the statements under else should be on the same scope as the loop itself.

Problematic code:

def find_even_number(numbers):
    for x in numbers:
        if x % 2 == 0:
            return x
    else:  # [useless-else-on-loop]
        print("Did not find an even number")

Correct code:

def find_even_number(numbers):
    for x in numbers:
        if x % 2 == 0:
            return x
    print("Did not find an even number")

Created by the basic checker.

  useless-param-doc / W9019

Message emitted:

"%s" useless ignored parameter documentation

Description:

Please remove the ignored parameter documentation.

Problematic code:

def say_hello(_new: str) -> str:  # [useless-param-doc]
    """say hello!
    :param _new:
    :return: comment
    """
    return "hello"

Correct code:

def say_hello(_new: str) -> str:
    """say hello!
    :return: comment
    """
    return "hello"

Configuration file:

[MAIN]
load-plugins=pylint.extensions.docparams,

NOTE:

This message is emitted by the optional 'parameter_documentation'
    checker which requires the pylint.extensions.docparams plugin to be loaded.

    Created by the parameter_documentation checker.

  useless-parent-delegation / W0246

Message emitted:

Useless parent or super() delegation in method %r

Description:

Used whenever we can detect that an overridden method is useless, relying on parent or super() delegation to do the same thing as another method from the MRO.

Problematic code:

class Animal:
    def eat(self, food):
        print(f"Eating {food}")
class Human(Animal):
    def eat(self, food):  # [useless-parent-delegation]
        super(Human, self).eat(food)

Correct code:

class Animal:
    def eat(self, food):
        print(f"Eating {food}")
class Human(Animal):
    """There is no need to override 'eat' it has the same signature as the implementation in Animal."""

Related links:

•   Stackoverflow explanation for 'useless-super-delegation'

    Created by the classes checker.

  useless-type-doc / W9020

Message emitted:

"%s" useless ignored parameter type documentation

Description:

Please remove the ignored parameter type documentation.

Problematic code:

def print_fruit(fruit, _):  # [useless-type-doc]
    """docstring ...
    Args:
        fruit (str): A fruit.
        _ (float): Another argument.
    """
    print(fruit)

Correct code:

def print_fruit(fruit):
    """docstring ...
    Args:
        fruit (str): A fruit.
    """
    print(fruit)

Configuration file:

[MAIN]
load-plugins=pylint.extensions.docparams,

NOTE:

This message is emitted by the optional 'parameter_documentation'
    checker which requires the pylint.extensions.docparams plugin to be loaded.

    Created by the parameter_documentation checker.

  useless-with-lock / W2101

Message emitted:

'%s()' directly created in 'with' has no effect

Description:

Used when a new lock instance is created by using with statement which has no effect. Instead, an existing instance should be used to acquire lock.

Problematic code:

import threading
with threading.Lock():  # [useless-with-lock]
    print("Make your bed.")
with threading.Lock():  # [useless-with-lock]
    print("Sleep in it")

Correct code:

import threading
lock = threading.Lock()
with lock:
    print("Make your bed.")
with lock:
    print("Sleep in it.")

Created by the threading checker.

  using-constant-test / W0125

Message emitted:

Using a conditional statement with a constant value

Description:

Emitted when a conditional statement (If or ternary if) uses a constant value for its test. This might not be what the user intended to do.

Problematic code:

if 0:  # [using-constant-test]
    print('This code is never executed.')
if 1:  # [using-constant-test]
    print('This code is always executed.')

Correct code:

print('This code is always executed.')

Created by the basic checker.

  using-f-string-in-unsupported-version / W2601

Message emitted:

F-strings are not supported by all versions included in the py-version setting

Description:

Used when the py-version set by the user is lower than 3.6 and pylint encounters a f-string.

Problematic code:

f"python {3.5} is past end of life"  # [using-f-string-in-unsupported-version]

Correct code:

"python {} is past end of life".format(3.5)

Configuration file:

[main]
py-version=3.5

Additional details:

f-strings were introduced in Python version 3.6; to use them, please use a more recent version of Python.

Created by the unsupported_version checker.

  using-final-decorator-in-unsupported-version / W2602

Message emitted:

typing.final is not supported by all versions included in the py-version setting

Description:

Used when the py-version set by the user is lower than 3.8 and pylint encounters a ``typing.final`` decorator.

Problematic code:

from typing import final
@final  # [using-final-decorator-in-unsupported-version]
class Playtypus(Animal):
    @final  # [using-final-decorator-in-unsupported-version]
    def lay_egg(self):
        ...

Correct code:

class Playtypus(Animal):
    def lay_egg(self):
        ...

Configuration file:

[main]
py-version=3.7

Additional details:

The message is emitted when the final decorator is used with a Python version less than 3.8. The final decorator was introduced in Python version 3.8.

Related links:

•   PEP 591

    Created by the unsupported_version checker.

  while-used / W0149

Message emitted:

Used `while` loop

Description:

Unbounded `while` loops can often be rewritten as bounded `for` loops. Exceptions can be made for cases such as event loops, listeners, etc.

Problematic code:

import requests
def fetch_data():
    i = 1
    while i < 6:  # [while-used]
        print(f'Attempt {i}...')
        try:
            return requests.get('https://example.com/data')
        except requests.exceptions.RequestException:
            pass
        i += 1

Correct code:

import requests
def fetch_data():
    for i in range(1, 6):
        print(f'Attempt {i}...')
        try:
            return requests.get('https://example.com/data')
        except requests.exceptions.RequestException:
            pass

Configuration file:

[main]
load-plugins=pylint.extensions.while_used

Related links:

•   Stackoverflow discussion

    NOTE:

This message is emitted by the optional 'while_used'
    checker which requires the pylint.extensions.while_used plugin to be loaded.

    Created by the while_used checker.

  wildcard-import / W0401

Message emitted:

Wildcard import %s

Description:

Used when `from module import *` is detected.

Problematic code:

from abc import *  # [wildcard-import]

Correct code:

# Either import module or
# only import required objects from module.
import abc
from abc import ABC, abstractmethod

Created by the imports checker.

  wrong-exception-operation / W0716

Message emitted:

Invalid exception operation. %s

Description:

Used when an operation is done against an exception, but the operation is not valid for the exception in question. Usually emitted when having binary operations between exceptions in except handlers.

Problematic code:

try:
    1/0
except (ValueError + TypeError):  # [wrong-exception-operation]
    pass

Correct code:

try:
    1/0
except (ValueError, TypeError):
    pass

Created by the exceptions checker.

All renamed messages in the warning category:

  broad-except / W0703

'broad-except' has been renamed. The new message can be found at:

  cache-max-size-none / W1517

'cache-max-size-none' has been renamed. The new message can be found at:

  implicit-str-concat-in-sequence / W1403

'implicit-str-concat-in-sequence' has been renamed. The new message can be found at:

  lru-cache-decorating-method / W1516

'lru-cache-decorating-method' has been renamed. The new message can be found at:

  old-assignment-from-none / W1111

'old-assignment-from-none' has been renamed. The new message can be found at:

  old-deprecated-argument / W1511

'old-deprecated-argument' has been renamed. The new message can be found at:

  old-deprecated-class / W1512

'old-deprecated-class' has been renamed. The new message can be found at:

  old-deprecated-decorator / W1513

'old-deprecated-decorator' has been renamed. The new message can be found at:

  old-deprecated-method / W1505

'old-deprecated-method' has been renamed. The new message can be found at:

  old-deprecated-module / W0402

'old-deprecated-module' has been renamed. The new message can be found at:

  old-empty-docstring / W0132

'old-empty-docstring' has been renamed. The new message can be found at:

  empty-docstring / C0112

Message emitted:

Empty %s docstring

Description:

Used when a module, function, class or method has an empty docstring (it would be too easy ;).

Problematic code:

def foo():  # [empty-docstring]
    """"""

Correct code:

def foo():
    """A dummy description."""

Created by the basic checker.

  old-missing-param-doc / W9003

'old-missing-param-doc' has been renamed. The new message can be found at:

  old-missing-returns-doc / W9007

'old-missing-returns-doc' has been renamed. The new message can be found at:

  old-missing-type-doc / W9004

'old-missing-type-doc' has been renamed. The new message can be found at:

  old-missing-yields-doc / W9009

'old-missing-yields-doc' has been renamed. The new message can be found at:

  old-non-iterator-returned-1 / W0234

'old-non-iterator-returned-1' has been renamed. The new message can be found at:

  old-unidiomatic-typecheck / W0154

'old-unidiomatic-typecheck' has been renamed. The new message can be found at:

  unidiomatic-typecheck / C0123

Message emitted:

Use isinstance() rather than type() for a typecheck.

Description:

The idiomatic way to perform an explicit typecheck in Python is to use isinstance(x, Y) rather than type(x) == Y, type(x) is Y. Though there are unusual situations where these give different results.

Problematic code:

test_score = {"Biology": 95, "History": 80}
if type(test_score) is dict:  # [unidiomatic-typecheck]
    pass

Correct code:

test_score = {"Biology": 95, "History": 80}
if isinstance(test_score, dict):
    pass

Related links:

•   Builtin function type()

•   Builtin function isinstance()

    Created by the basic checker.

  old-unpacking-non-sequence / W0633

'old-unpacking-non-sequence' has been renamed. The new message can be found at:

  useless-super-delegation / W0235

'useless-super-delegation' has been renamed. The new message can be found at:

  Convention

All messages in the convention category:

  bad-classmethod-argument / C0202

Message emitted:

Class method %s should have %s as first argument

Description:

Used when a class method has a first argument named differently than the value specified in valid-classmethod-first-arg option (default to "cls"), recommended to easily differentiate them from regular instance methods.

Problematic code:

class Klass:
    @classmethod
    def get_instance(self):  # [bad-classmethod-argument]
        return self()

Correct code:

class Klass:
    @classmethod
    def get_instance(cls):
        return cls()

Created by the classes checker.

  bad-docstring-quotes / C0198

Message emitted:

Bad docstring quotes in %s, expected """, given %s

Description:

Used when a docstring does not have triple double quotes.

Problematic code:

def foo():  # [bad-docstring-quotes]
    'Docstring.'
    return

Correct code:

def foo():
    """Docstring."""
    return

Configuration file:

[main]
load-plugins=pylint.extensions.docstyle

Additional details:

From PEP 257:
    "For consistency, always use """triple double quotes""" around docstrings."

    Related links:

•   PEP 257 – Docstring Conventions

    NOTE:

This message is emitted by the optional 'docstyle'
    checker which requires the pylint.extensions.docstyle plugin to be loaded.

    Created by the docstyle checker.

  bad-file-encoding / C2503

Message emitted:

PEP8 recommends UTF-8 as encoding for Python files

Description:

PEP8 recommends UTF-8 default encoding for Python files. See https://peps.python.org/pep-0008/#source-file-encoding

Correct code:

# This is a placeholder for correct code for this message.

Additional details:

You can help us make the doc better by contributing !

Created by the unicode_checker checker.

  bad-mcs-classmethod-argument / C0204

Message emitted:

Metaclass class method %s should have %s as first argument

Description:

Used when a metaclass class method has a first argument named differently than the value specified in valid-metaclass-classmethod-first-arg option (default to "mcs"), recommended to easily differentiate them from regular instance methods.

Problematic code:

class Meta(type):
    @classmethod
    def foo(some):  # [bad-mcs-classmethod-argument]
        pass

Correct code:

class Meta(type):
    @classmethod
    def foo(mcs):
        pass

Created by the classes checker.

  bad-mcs-method-argument / C0203

Message emitted:

Metaclass method %s should have %s as first argument

Description:

Used when a metaclass method has a first argument named differently than the value specified in valid-classmethod-first-arg option (default to "cls"), recommended to easily differentiate them from regular instance methods.

Problematic code:

class Meta(type):
    def func(some):  # [bad-mcs-method-argument]
        pass

Correct code:

class Meta(type):
    def func(cls):
        pass

Created by the classes checker.

  compare-to-empty-string / C1901

Message emitted:

"%s" can be simplified to "%s" as an empty string is falsey

Description:

Used when Pylint detects comparison to an empty string constant.

Problematic code:

x = ""
y = "hello"
if x == "":  # [compare-to-empty-string]
    print("x is an empty string")
if y != "":  # [compare-to-empty-string]
    print("y is not an empty string")

Correct code:

x = ""
y = "hello"
if not x:
    print("x is an empty string")
if y:
    print("y is not an empty string")

Configuration file:

[main]
load-plugins=pylint.extensions.emptystring

NOTE:

This message is emitted by the optional 'compare-to-empty-string'
    checker which requires the pylint.extensions.emptystring plugin to be loaded.

    Created by the compare-to-empty-string checker.

  compare-to-zero / C2001

Message emitted:

"%s" can be simplified to "%s" as 0 is falsey

Description:

Used when Pylint detects comparison to a 0 constant.

Problematic code:

x = 0
y = 1
if x == 0:   # [compare-to-zero]
    print("x is equal to zero")
if y != 0:   # [compare-to-zero]
    print("y is not equal to zero")

Correct code:

x = 0
y = 1
if not x:
    print("x is equal to zero")
if y:
    print("y is not equal to zero")

Configuration file:

[main]
load-plugins=pylint.extensions.comparetozero

NOTE:

This message is emitted by the optional 'compare-to-zero'
    checker which requires the pylint.extensions.comparetozero plugin to be loaded.

    Created by the compare-to-zero checker.

  consider-iterating-dictionary / C0201

Message emitted:

Consider iterating the dictionary directly instead of calling .keys()

Description:

Emitted when the keys of a dictionary are iterated through the ``.keys()`` method or when ``.keys()`` is used for a membership check. It is enough to iterate through the dictionary itself, ``for key in dictionary``. For membership checks, ``if key in dictionary`` is faster.

Problematic code:

FRUITS = {"apple": 1, "pear": 5, "peach": 10}
for fruit in FRUITS.keys():  # [consider-iterating-dictionary]
    print(fruit)

Correct code:

FRUITS = {"apple": 1, "pear": 5, "peach": 10}
for fruit in FRUITS:
    print(fruit)

Created by the refactoring checker.

  consider-using-any-or-all / C0501

Message emitted:

`for` loop could be `%s`

Description:

A for loop that checks for a condition and return a bool can be replaced with any or all.

Problematic code:

def any_even(items):
    """Return True if the list contains any even numbers"""
    for item in items:  # [consider-using-any-or-all]
        if item % 2 == 0:
            return True
    return False
def all_even(items):
    """Return True if the list contains all even numbers"""
    for item in items:  # [consider-using-any-or-all]
        if not item % 2 == 0:
            return False
    return True

Correct code:

def any_even(items):
    """Return True if the list contains any even numbers"""
    return any(item % 2 == 0 for item in items)
def all_even(items):
    """Return True if the list contains all even numbers"""
    return all(item % 2 == 0 for item in items)

Configuration file:

[MAIN]
load-plugins=pylint.extensions.for_any_all

NOTE:

This message is emitted by the optional 'consider-using-any-or-all'
    checker which requires the pylint.extensions.for_any_all plugin to be loaded.

    Created by the consider-using-any-or-all checker.

  consider-using-dict-items / C0206

Message emitted:

Consider iterating with .items()

Description:

Emitted when iterating over the keys of a dictionary and accessing the value by index lookup. Both the key and value can be accessed by iterating using the .items() method of the dictionary instead.

Problematic code:

ORCHESTRA = {
    "violin": "strings",
    "oboe": "woodwind",
    "tuba": "brass",
    "gong": "percussion",
}
for instrument in ORCHESTRA:  # [consider-using-dict-items]
    print(f"{instrument}: {ORCHESTRA[instrument]}")

Correct code:

ORCHESTRA = {
    "violin": "strings",
    "oboe": "woodwind",
    "tuba": "brass",
    "gong": "percussion",
}
for instrument, section in ORCHESTRA.items():
    print(f"{instrument}: {section}")

Created by the refactoring checker.

  consider-using-enumerate / C0200

Message emitted:

Consider using enumerate instead of iterating with range and len

Description:

Emitted when code that iterates with range and len is encountered. Such code can be simplified by using the enumerate builtin.

Problematic code:

seasons = ['Spring', 'Summer', 'Fall', 'Winter']
for i in range(len(seasons)):  # [consider-using-enumerate]
    print(i, seasons[i])

Correct code:

seasons = ['Spring', 'Summer', 'Fall', 'Winter']
for i, season in enumerate(seasons):
    print(i, season)

Created by the refactoring checker.

  consider-using-f-string / C0209

Message emitted:

Formatting a regular string which could be a f-string

Description:

Used when we detect a string that is being formatted with format() or % which could potentially be a f-string. The use of f-strings is preferred. Requires Python 3.6 and ``py-version >= 3.6``.

Problematic code:

from string import Template
menu = ("eggs", "spam", 42.4)
old_order = "%s and %s: %.2f ¤" % menu  # [consider-using-f-string]
beginner_order = menu[0] + " and " + menu[1] + ": " + str(menu[2]) + " ¤"
joined_order = " and ".join(menu[:2])
# +1: [consider-using-f-string]
format_order = "{} and {}: {:0.2f} ¤".format(menu[0], menu[1], menu[2])
# +1: [consider-using-f-string]
named_format_order = "{eggs} and {spam}: {price:0.2f} ¤".format(
    eggs=menu[0], spam=menu[1], price=menu[2]
)
template_order = Template("$eggs and $spam: $price ¤").substitute(
    eggs=menu[0], spam=menu[1], price=menu[2]
)

Correct code:

menu = ('eggs', 'spam', 42.4)
f_string_order = f"{menu[0]} and {menu[1]}: {menu[2]:0.2f} ¤"

Additional details:

Formatted string literals (f-strings) give a concise, consistent syntax that can replace most use cases for the % formatting operator, str.format() and string.Template.

F-strings also perform better than alternatives; see this tweet for a simple example.

Created by the refactoring checker.

  dict-init-mutate / C3401

Message emitted:

Declare all known key/values when initializing the dictionary.

Description:

Dictionaries can be initialized with a single statement using dictionary literal syntax.

Problematic code:

fruit_prices = {}  # [dict-init-mutate]
fruit_prices['apple'] = 1
fruit_prices['banana'] = 10

Correct code:

fruit_prices = {"apple": 1, "banana": 10}

Configuration file:

[MAIN]
load-plugins=pylint.extensions.dict_init_mutate,

NOTE:

This message is emitted by the optional 'dict-init-mutate'
    checker which requires the pylint.extensions.dict_init_mutate plugin to be loaded.

    Created by the dict-init-mutate checker.

  disallowed-name / C0104

Message emitted:

Disallowed name "%s"

Description:

Used when the name matches bad-names or bad-names-rgxs- (unauthorized names).

Problematic code:

def foo():  # [disallowed-name]
    print("apples")

Correct code:

def print_fruit():
    print("apples")

Configuration file:

[MAIN]
bad-names=foo,bar,baz

Created by the basic checker.

  docstring-first-line-empty / C0199

Message emitted:

First line empty in %s docstring

Description:

Used when a blank line is found at the beginning of a docstring.

Problematic code:

def foo():  # [docstring-first-line-empty]
    """
    Lorem Ipsum is simply dummy text of the printing and typesetting
    industry.
    Lorem Ipsum has been the industry's standard dummy text ever since the
    1500s, when an unknown printer took a galley of type and scrambled it
    to make a type specimen book
    """

Correct code:

def foo():
    """Lorem Ipsum is simply dummy text of the printing and typesetting
    industry.
    Lorem Ipsum has been the industry's standard dummy text ever since the
    1500s, when an unknown printer took a galley of type and scrambled it
    to make a type specimen book
    """

Configuration file:

[MAIN]
load-plugins = pylint.extensions.docstyle

NOTE:

This message is emitted by the optional 'docstyle'
    checker which requires the pylint.extensions.docstyle plugin to be loaded.

    Created by the docstyle checker.

  import-outside-toplevel / C0415

Message emitted:

Import outside toplevel (%s)

Description:

Used when an import statement is used anywhere other than the module toplevel. Move this import to the top of the file.

Problematic code:

def print_python_version():
    import sys  # [import-outside-toplevel]
    print(sys.version_info)

Correct code:

import sys
def print_python_version():
    print(sys.version_info)

Created by the imports checker.

  import-private-name / C2701

Message emitted:

Imported private %s (%s)

Description:

Used when a private module or object prefixed with _ is imported. PEP8 guidance on Naming Conventions states that public attributes with leading underscores should be considered private.

Problematic code:

from argparse import _AttributeHolder, _SubParsersAction  # [import-private-name]
attr_holder = _AttributeHolder()
def add_sub_parser(sub_parsers: _SubParsersAction):
    sub_parsers.add_parser('my_subparser')
    # ...

Correct code:

"""Private import can be used as type annotations."""
from argparse import _SubParsersAction
def add_sub_parser(sub_parsers: _SubParsersAction):
    sub_parsers.add_parser('my_subparser')
    # ...

Configuration file:

[main]
load-plugins = pylint.extensions.private_import

Additional details:

Using private imports expose you to unexpected breaking changes for any version bump of your dependencies, even in patch versions.

NOTE:

This message is emitted by the optional 'import-private-name'
    checker which requires the pylint.extensions.private_import plugin to be loaded.

    Created by the import-private-name checker.

  invalid-characters-in-docstring / C0403

Message emitted:

Invalid characters %r in a docstring

Description:

Used when a word in docstring cannot be checked by enchant.

Additional details:

This is a message linked to an internal problem in enchant. There's nothing to change in your code, but maybe in pylint's configuration or the way you installed the 'enchant' system library.

Created by the spelling checker.

  invalid-name / C0103

Message emitted:

%s name "%s" doesn't conform to %s

Description:

Used when the name doesn't conform to naming rules associated to its type (constant, variable, class...).

Problematic code:

class cat:  # [invalid-name]
    def Meow(self, NUMBER_OF_MEOW):  # [invalid-name, invalid-name]
        print("Meow" * NUMBER_OF_MEOW)
        return NUMBER_OF_MEOW
Cat = cat().Meow(42)  # [invalid-name]

Correct code:

class Cat:
    def meow(self, number_of_meow):
        print("Meow" * number_of_meow)
        return number_of_meow
CAT = Cat().meow(42)

Additional details:

Pylint recognizes a number of different name types internally. With a few exceptions, the type of the name is governed by the location the assignment to a name is found in, and not the type of object assigned.
Name Type | Description
module | Module and package names, same as the file names.
const | Module-level constants, any variable defined at module level that is not bound to a class object.
class | Names in class statements, as well as names bound to class objects at module level.
function | Functions, toplevel or nested in functions or methods.
method | Methods, functions defined in class bodies. Includes static and class methods.
attr | Attributes created on class instances inside methods.
argument | Arguments to any function type, including lambdas.
variable | Local variables in function scopes.
class-attribute | Attributes defined in class bodies.
class-const | Enum constants and class variables annotated with ClassVar
inlinevar | Loop variables in list comprehensions and generator expressions.
typevar | Type variable declared with TypeVar.
typealias | Type alias declared with TypeAlias or assignments of Union.

  Default behavior

By default, Pylint will enforce PEP8-suggested names.

  Predefined Naming Styles

Pylint provides set of predefined naming styles. Those predefined naming styles may be used to adjust Pylint configuration to coding style used in linted project.

Following predefined naming styles are available:

•   snake_case

•   camelCase

•   PascalCase

•   UPPER_CASE

•   any - fake style which does not enforce any limitations

    Following options are exposed:

--module-naming-style=<style>

--const-naming-style=<style>

--class-naming-style=<style>

--function-naming-style=<style>

--method-naming-style=<style>

--attr-naming-style=<style>

--argument-naming-style=<style>

--variable-naming-style=<style>

--class-attribute-naming-style=<style>

--class-const-naming-style=<style>

--inlinevar-naming-style=<style>

  Predefined Naming Patterns

Pylint provides predefined naming patterns for some names. These patterns are often based on a Naming Style but there is no option to choose one of the styles mentioned above. The pattern can be overwritten with the options discussed below.

The following type of names are checked with a predefined pattern:
Name type | Good names | Bad names
typevar | T, _CallableT, _T_co, AnyStr, DeviceTypeT, IPAddressT | DICT_T, CALLABLE_T, ENUM_T, DeviceType, _StrType
typealias | GoodName2 and other PascalCase variants that don't start with T or Type. This is to distinguish them from typevars. Note that TopName is allowed but TTopName isn't. | _1BadName

  Custom regular expressions

If predefined naming styles are too limited, checker behavior may be further customized. For each name type, a separate regular expression matching valid names of this type can be defined. If any of custom regular expressions are defined, it overrides *-naming-style option value.

Regular expressions for the names are anchored at the beginning, any anchor for the end must be supplied explicitly. Any name not matching the regular expression will lead to an instance of invalid-name.

--module-rgx=<regex>

--const-rgx=<regex>

--class-rgx=<regex>

--function-rgx=<regex>

--method-rgx=<regex>

--attr-rgx=<regex>

--argument-rgx=<regex>

--variable-rgx=<regex>

--class-attribute-rgx=<regex>

--class-const-rgx=<regex>

--inlinevar-rgx=<regex>

--typevar-rgx=<regex>

--typealias-rgx=<regex>

  Multiple naming styles for custom regular expressions

Large code bases that have been worked on for multiple years often exhibit an evolution in style as well. In some cases, modules can be in the same package, but still have different naming style based on the stratum they belong to. However, intra-module consistency should still be required, to make changes inside a single file easier. For this case, Pylint supports regular expression with several named capturing group.

Rather than emitting name warnings immediately, Pylint will determine the prevalent naming style inside each module and enforce it on all names.

Consider the following (simplified) example:

pylint --function-rgx='(?:(?P<snake>[a-z_]+)|(?P<camel>[a-z]+([A-Z][a-z]*)*))$' sample.py

The regular expression defines two naming styles, snake for snake-case names, and camel for camel-case names.

In sample.py, the function name on line 1 and 7 will mark the module and enforce the match of named group snake for the remaining names in the module:

def valid_snake_case(arg):
   ...
def InvalidCamelCase(arg):
   ...
def more_valid_snake_case(arg):
 ...

Because of this, the name on line 4 will trigger an invalid-name warning, even though the name matches the given regex.

Matches named exempt or ignore can be used for non-tainting names, to prevent built-in or interface-dictated names to trigger certain naming styles.

--name-group=<name1:name2:...,...>
    Default value: empty

    Format: comma-separated groups of colon-separated names.

    This option can be used to combine name styles. For example, function:method enforces that functions and methods use the same style, and a style triggered by either name type carries over to the other. This requires that the regular expression for the combined name types use the same group names.

  Name Hints

--include-naming-hint=y|n
    Default: off

    Include a hint (regular expression used) for the correct name format with every invalid-name warning.

    Created by the basic checker.

  line-too-long / C0301

Message emitted:

Line too long (%s/%s)

Description:

Used when a line is longer than a given number of characters.

Problematic code:

# +1: [line-too-long]
FRUIT = ["apricot", "blackcurrant", "cantaloupe", "dragon fruit", "elderberry", "fig", "grapefruit", ]

Correct code:

FRUIT = [
    "apricot",
    "blackcurrant",
    "cantaloupe",
    "dragon fruit",
    "elderberry",
    "fig",
    "grapefruit",
]

Configuration file:

[MAIN]
max-line-length=100

Additional details:

Pragma controls such as # pylint: disable=all are not counted toward line length for the purposes of this message.

If you attempt to disable this message via # pylint: disable=line-too-long in a module with no code, you may receive a message for useless-suppression. This is a false positive of useless-suppression we can't easily fix.

See https://github.com/PyCQA/pylint/issues/3368 for more information.

Created by the format checker.

  misplaced-comparison-constant / C2201

Message emitted:

Comparison should be %s

Description:

Used when the constant is placed on the left side of a comparison. It is usually clearer in intent to place it in the right hand side of the comparison.

Problematic code:

def compare_apples(apples=20):
    for i in range(10):
        if 5 <= i:  # [misplaced-comparison-constant]
            pass
        if 1 == i:  # [misplaced-comparison-constant]
            pass
        if 20 < len(apples):  # [misplaced-comparison-constant]
            pass

Correct code:

def compare_apples(apples=20):
    for i in range(10):
        if i >= 5:
            pass
        if i == 1:
            pass
        if len(apples) > 20:
            pass

Configuration file:

[MAIN]
load-plugins=pylint.extensions.comparison_placement

NOTE:

This message is emitted by the optional 'comparison-placement'
    checker which requires the pylint.extensions.comparison_placement plugin to be loaded.

    Created by the comparison-placement checker.

  missing-class-docstring / C0115

Message emitted:

Missing class docstring

Description:

Used when a class has no docstring. Even an empty class must have a docstring.

Problematic code:

class Person:  # [missing-class-docstring]
    def __init__(self, first_name, last_name):
        self.first_name = first_name
        self.last_name = last_name

Correct code:

class Person:
    """Class representing a person"""
    def __init__(self, first_name, last_name):
        self.first_name = first_name
        self.last_name = last_name

Created by the basic checker.

  missing-final-newline / C0304

Message emitted:

Final newline missing

Description:

Used when the last line in a file is missing a newline.

Problematic code:

# using LF
eat("apple", "candy")  # \n
print(123)  # EOF
# using CRLF
eat("apple", "candy")  # \r\n
print(123)  # EOF
# [missing-final-newline]

Correct code:

# using LF
eat("apple", "candy") #  \n
print(123)  # \nEOF
# using CRLF
eat("apple", "candy")  # \r\n
print(123)  # \r\nEOF

Additional details:

The POSIX standard defines a line as:
    "A sequence of zero or more non- <newline> characters plus a terminating <newline> character."

    Related links:

•   POSIX Standard

•   POSIX Standard Chapter 3.206 Line

    Created by the format checker.

  missing-function-docstring / C0116

Message emitted:

Missing function or method docstring

Description:

Used when a function or method has no docstring. Some special methods like __init__ do not require a docstring.

Problematic code:

import sys
def print_python_version():  # [missing-function-docstring]
    print(sys.version)

Correct code:

import sys
def print_python_version():
    """Function printing python version."""
    print(sys.version)

Created by the basic checker.

  missing-module-docstring / C0114

Message emitted:

Missing module docstring

Description:

Used when a module has no docstring. Empty modules do not require a docstring.

Problematic code:

import sys  # [missing-module-docstring]
def print_python_version():
    print(sys.version)

Correct code:

"""Module providingFunction printing python version."""
import sys
def print_python_version():
    print(sys.version)

Created by the basic checker.

  mixed-line-endings / C0327

Message emitted:

Mixed line endings LF and CRLF

Description:

Used when there are mixed (LF and CRLF) newline signs in a file.

Correct code:

# This is a placeholder for correct code for this message.

Additional details:

You can help us make the doc better by contributing !

Created by the format checker.

  multiple-imports / C0410

Message emitted:

Multiple imports on one line (%s)

Description:

Used when import statement importing multiple modules is detected.

Problematic code:

import os, sys  # [multiple-imports]

Correct code:

import os
import sys

Created by the imports checker.

  multiple-statements / C0321

Message emitted:

More than one statement on a single line

Description:

Used when more than on statement are found on the same line.

Problematic code:

fruits = ["apple", "orange", "mango"]
if "apple" in fruits: pass  # [multiple-statements]
else:
    print("no apples!")

Correct code:

fruits = ["apple", "orange", "mango"]
if "apple" in fruits:
    pass
else:
    print("no apples!")

Created by the format checker.

  non-ascii-module-import / C2403

Message emitted:

%s name "%s" contains a non-ASCII character, use an ASCII-only alias for import.

Description:

Used when the name contains at least one non-ASCII unicode character. See https://peps.python.org/pep-0672/#confusing-features for a background why this could be bad. If your programming guideline defines that you are programming in English, then there should be no need for non ASCII characters in Python Names. If not you can simply disable this check.

Problematic code:

from os.path import join as łos  # [non-ascii-module-import]
foo = łos("a", "b")

Correct code:

from os.path import join as os_join
foo = os_join("a", "b")

Created by the nonascii-checker checker.

  non-ascii-name / C2401

Message emitted:

%s name "%s" contains a non-ASCII character, consider renaming it.

Description:

Used when the name contains at least one non-ASCII unicode character. See https://peps.python.org/pep-0672/#confusing-features for a background why this could be bad. If your programming guideline defines that you are programming in English, then there should be no need for non ASCII characters in Python Names. If not you can simply disable this check.

Problematic code:

ápple_count = 4444  # [non-ascii-name]

Correct code:

apple_count = 4444

Created by the nonascii-checker checker.

  single-string-used-for-slots / C0205

Message emitted:

Class __slots__ should be a non-string iterable

Description:

Used when a class __slots__ is a simple string, rather than an iterable.

Problematic code:

class Fruit:  # [single-string-used-for-slots]
    __slots__ = "name"
    def __init__(self, name):
        self.name = name

Correct code:

class Fruit:
    __slots__ = ("name",)
    def __init__(self, name):
        self.name = name

Created by the classes checker.

  singleton-comparison / C0121

Message emitted:

Comparison %s should be %s

Description:

Used when an expression is compared to singleton values like True, False or None.

Problematic code:

game_won = True
if game_won == True:  # [singleton-comparison]
    print("Game won !")

Correct code:

game_won = True
if game_won:
    print("Game won !")

Related links:

•   PEP 285 – Adding a bool type

    Created by the basic checker.

  superfluous-parens / C0325

Message emitted:

Unnecessary parens after %r keyword

Description:

Used when a single item in parentheses follows an if, for, or other keyword.

Problematic code:

x = input()
y = input()
if (x == y):  # [superfluous-parens]
    pass
i = 0
exclude = []
if (i - 0) in exclude:  # [superfluous-parens]
    pass

Correct code:

x = input()
y = input()
if x == y:
    pass
i = 0
exclude = []
if i - 0 in exclude:
    pass

Created by the format checker.

  too-many-lines / C0302

Message emitted:

Too many lines in module (%s/%s)

Description:

Used when a module has too many lines, reducing its readability.

Problematic code:

def is_palindrome(string):  # [too-many-lines]
    left_pos = 0
    right_pos = len(string) - 1
    while right_pos >= left_pos:
        if not string[left_pos] == string[right_pos]:
            return False
        left_pos += 1
        right_pos -= 1
    return True
def main():
    print(isPalindrome("aza"))
    print(isPalindrome("racecar"))
    print(isPalindrome("trigger"))
    print(isPalindrome("ogre"))

Correct code:

__init__.py:

__all__ = ["is_palindrome", "main"]
from is_palindrome import is_palindrome
from main import main

is_palindrome.py:

def is_palindrome(string):
    return string == string[::-1]

main.py:

from is_palindrome import is_palindrome
def main():
    for string in ["aza", "racecar", "trigger", "ogre"]:
        print(is_palindrome(string))

Configuration file:

[main]
max-module-lines=15

Additional details:

When a module has too many lines it can make it difficult to read and understand. There might be performance issue while editing the file because the IDE must parse more code. You need more expertise to navigate the file properly (go to a particular line when debugging, or search for a specific code construct, instead of navigating by clicking and scrolling)

This measure is a proxy for higher cyclomatic complexity that you might not be calculating if you're not using load-plugins=pylint.extensions.mccabe,. Cyclomatic complexity is slower to compute, but also a more fine grained measure than raw SLOC. In particular, you can't make the code less readable by making a very complex one liner if you're using cyclomatic complexity.

The example simplify the code, but it's not always possible. Most of the time bursting the file by creating a package with the same API is the only solution. Anticipating and creating the file from the get go will permit to have the same end result with a better version control history.

Created by the format checker.

  trailing-newlines / C0305

Message emitted:

Trailing newlines

Description:

Used when there are trailing blank lines in a file.

Problematic code:

print("apple")
# The file ends with 2 lines that are empty # +1: [trailing-newlines]

Correct code:

print("apple")

Created by the format checker.

  trailing-whitespace / C0303

Message emitted:

Trailing whitespace

Description:

Used when there is whitespace between the end of a line and the newline.

Problematic code:

print("Hello")  # [trailing-whitespace]
#                                       ^^^ trailing whitespaces

Correct code:

print("Hello")

Created by the format checker.

  typevar-double-variance / C0131

Message emitted:

TypeVar cannot be both covariant and contravariant

Description:

Emitted when both the "covariant" and "contravariant" keyword arguments are set to "True" in a TypeVar.

Problematic code:

from typing import TypeVar
T = TypeVar("T", covariant=True, contravariant=True)  # [typevar-double-variance]

Correct code:

from typing import TypeVar
T_co = TypeVar("T_co", covariant=True)
T_contra = TypeVar("T_contra", contravariant=True)

Created by the basic checker.

  typevar-name-incorrect-variance / C0105

Message emitted:

Type variable name does not reflect variance%s

Description:

Emitted when a TypeVar name doesn't reflect its type variance. According to PEP8, it is recommended to add suffixes '_co' and '_contra' to the variables used to declare covariant or contravariant behaviour respectively. Invariant (default) variables do not require a suffix. The message is also emitted when invariant variables do have a suffix.

Problematic code:

from typing import TypeVar
T_co = TypeVar("T_co")  # [typevar-name-incorrect-variance]

Correct code:

from typing import TypeVar
T = TypeVar("T")

Created by the basic checker.

  typevar-name-mismatch / C0132

Message emitted:

TypeVar name "%s" does not match assigned variable name "%s"

Description:

Emitted when a TypeVar is assigned to a variable that does not match its name argument.

Problematic code:

from typing import TypeVar
X = TypeVar("T")  # [typevar-name-mismatch]

Correct code:

from typing import TypeVar
T = TypeVar("T")

Created by the basic checker.

  unexpected-line-ending-format / C0328

Message emitted:

Unexpected line ending format. There is '%s' while it should be '%s'.

Description:

Used when there is different newline than expected.

Problematic code:

print("Sometimes I drink soda.")  # CRLF # [unexpected-line-ending-format]
print("Sometimes I drink sulfuric acid.")  # CRLF # [unexpected-line-ending-format]

Correct code:

print("I'm drinking tea!")  # LF
print("I'm drinking water!")  # LF

Configuration file:

[FORMAT]
expected-line-ending-format=LF

Related links:

•   History of CRLF and LF

•   Dealing with line endings in Git

•   A Collection of Useful .gitattributes Templates

    Created by the format checker.

  ungrouped-imports / C0412

Message emitted:

Imports from package %s are not grouped

Description:

Used when imports are not grouped by packages.

Problematic code:

import logging
import os
import sys
import logging.config  # [ungrouped-imports]
from logging.handlers import WatchedFileHandler

Correct code:

import logging
import logging.config
import os
import sys
from logging.handlers import FileHandler

Created by the imports checker.

  unnecessary-direct-lambda-call / C3002

Message emitted:

Lambda expression called directly. Execute the expression inline instead.

Description:

Used when a lambda expression is directly called rather than executing its contents inline.

Problematic code:

y = (lambda x: x**2 + 2*x + 1)(a)  # [unnecessary-direct-lambda-call]

Correct code:

y = a**2 + 2*a + 1

Created by the lambda-expressions checker.

  unnecessary-dunder-call / C2801

Message emitted:

Unnecessarily calls dunder method %s. %s.

Description:

Used when a dunder method is manually called instead of using the corresponding function/method/operator.

Problematic code:

three = 3.0.__str__()  # [unnecessary-dunder-call]
twelve = "1".__add__("2")  # [unnecessary-dunder-call]
def is_bigger_than_two(x):
    return x.__gt__(2)  # [unnecessary-dunder-call]

Correct code:

three = str(3.0)
twelve = "1" + "2"
def is_bigger_than_two(x):
    return x > 2

Created by the unnecessary-dunder-call checker.

  unnecessary-lambda-assignment / C3001

Message emitted:

Lambda expression assigned to a variable. Define a function using the "def" keyword instead.

Description:

Used when a lambda expression is assigned to variable rather than defining a standard function with the "def" keyword.

Problematic code:

foo = lambda x: x**2 + 2*x + 1  # [unnecessary-lambda-assignment]

Correct code:

def foo(x):
    return x**2 + 2*x + 1

Created by the lambda-expressions checker.

  unneeded-not / C0113

Message emitted:

Consider changing "%s" to "%s"

Description:

Used when a boolean expression contains an unneeded negation.

Problematic code:

if not not input():  # [unneeded-not]
    pass

Correct code:

if input():
    pass

Created by the refactoring checker.

  use-implicit-booleaness-not-comparison / C1803

Message emitted:

'%s' can be simplified to '%s' as an empty %s is falsey

Description:

Used when Pylint detects that collection literal comparison is being used to check for emptiness; Use implicit booleaness instead of a collection classes; empty collections are considered as false

Problematic code:

z = []
if z != []:  # [use-implicit-booleaness-not-comparison]
    print("z is not an empty sequence")

Correct code:

z = []
if z:
    print("z is not an empty sequence")

Created by the refactoring checker.

  use-implicit-booleaness-not-len / C1802

Message emitted:

Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty

Description:

Used when Pylint detects that len(sequence) is being used without explicit comparison inside a condition to determine if a sequence is empty. Instead of coercing the length to a boolean, either rely on the fact that empty sequences are false or compare the length against a scalar.

Problematic code:

fruits = ["orange", "apple"]
if len(fruits):  # [use-implicit-booleaness-not-len]
    print(fruits)

Correct code:

fruits = ["orange", "apple"]
if fruits:
    print(fruits)

Created by the refactoring checker.

  use-maxsplit-arg / C0207

Message emitted:

Use %s instead

Description:

Emitted when accessing only the first or last element of str.split(). The first and last element can be accessed by using str.split(sep, maxsplit=1)[0] or str.rsplit(sep, maxsplit=1)[-1] instead.

Problematic code:

url = "www.example.com"
suffix = url.split(".")[-1]  # [use-maxsplit-arg]

Correct code:

url = "www.example.com"
suffix = url.rsplit(".", maxsplit=1)[-1]

Additional details:

Be aware that the performance improvement from not splitting the string so many times will only be realized in cases presenting more instances of the splitting character than the minimal example here.

Created by the refactoring checker.

  use-sequence-for-iteration / C0208

Message emitted:

Use a sequence type when iterating over values

Description:

When iterating over values, sequence types (e.g., ``lists``, ``tuples``, ``ranges``) are more efficient than ``sets``.

Problematic code:

for food in {"apples", "lemons", "water"}:  # [use-sequence-for-iteration]
    print(f"I like {food}.")

Correct code:

# as list
for food in ["apples", "lemons", "water"]:
    print(f"I like {food}.")
# as tuple
for food in ("apples", "lemons", "water"):
    print(f"I like {food}.")

Additional details:

https://gist.github.com/hofrob/8b1c1e205a0d4c66a680b1fe4bfeba11

This example script shows a significant increase in performance when using a list, tuple or range over a set in python version 3.11.1.

Created by the refactoring checker.

  useless-import-alias / C0414

Message emitted:

Import alias does not rename original package

Description:

Used when an import alias is same as original package, e.g., using import numpy as numpy instead of import numpy as np.

Problematic code:

import pandas as pandas  # [useless-import-alias]

Correct code:

import pandas as pd

Additional details:

  Known issue

If you prefer to use "from-as" to explicitly reexport in API (from fruit import orange as orange) instead of using __all__ this message will be a false positive.

Use --allow-reexport-from-package to allow explicit reexports by alias in package __init__ files.

Related links:

•   --allow-reexport-from-package

•   PEP 8, Import Guideline

•   Pylint block-disable

•   mypy --no-implicit-reexport

    Created by the imports checker.

  wrong-import-order / C0411

Message emitted:

%s should be placed before %s

Description:

Used when PEP8 import order is not respected (standard imports first, then third-party libraries, then local imports).

Problematic code:

import os
from . import utils
import pylint  # [wrong-import-order]
import sys  # [wrong-import-order]

Correct code:

import os
import sys
import pylint
from . import utils

Created by the imports checker.

  wrong-import-position / C0413

Message emitted:

Import "%s" should be placed at the top of the module

Description:

Used when code and imports are mixed.

Problematic code:

import os
home = os.environ['HOME']
import sys  # [wrong-import-position]
print(f'Home directory is {home}', file=sys.stderr)

Correct code:

import os
import sys
home = os.environ['HOME']
print(f'Home directory is {home}', file=sys.stderr)

Created by the imports checker.

  wrong-spelling-in-comment / C0401

Message emitted:

Wrong spelling of a word '%s' in a comment: %s %s Did you mean: '%s'?

Description:

Used when a word in comment is not spelled correctly.

Problematic code:

# There's a mistkae in this string  # [wrong-spelling-in-comment]

Correct code:

# There's no mistake in this string

Configuration file:

[main]
# This might not run in your env if you don't have the en_US dict installed.
spelling-dict=en_US

Created by the spelling checker.

  wrong-spelling-in-docstring / C0402

Message emitted:

Wrong spelling of a word '%s' in a docstring: %s %s Did you mean: '%s'?

Description:

Used when a word in docstring is not spelled correctly.

Problematic code:

"""There's a mistkae in this string"""  # [wrong-spelling-in-docstring]

Correct code:

"""There's no mistake in this string"""

Configuration file:

[main]
# This might not run in your env if you don't have the en_US dict installed.
spelling-dict=en_US

Created by the spelling checker.

All renamed messages in the convention category:

  blacklisted-name / C0102

'blacklisted-name' has been renamed. The new message can be found at:

  len-as-condition / C1801

'len-as-condition' has been renamed. The new message can be found at:

  missing-docstring / C0111

'missing-docstring' has been renamed. The new message can be found at:

  old-misplaced-comparison-constant / C0122

'old-misplaced-comparison-constant' has been renamed. The new message can be found at:

  old-non-ascii-name / C0144

'old-non-ascii-name' has been renamed. The new message can be found at:

  Refactor

All messages in the refactor category:

  chained-comparison / R1716

Message emitted:

Simplify chained comparison between the operands

Description:

This message is emitted when pylint encounters boolean operation like "a < b and b < c", suggesting instead to refactor it to "a < b < c"

Problematic code:

a = int(input())
b = int(input())
c = int(input())
if a < b and b < c:  # [chained-comparison]
    pass

Correct code:

a = int(input())
b = int(input())
c = int(input())
if a < b < c:
    pass

Created by the refactoring checker.

  comparison-of-constants / R0133

Message emitted:

Comparison between constants: '%s %s %s' has a constant value

Description:

When two literals are compared with each other the result is a constant. Using the constant directly is both easier to read and more performant. Initializing 'True' and 'False' this way is not required since Python 2.3.

Problematic code:

def is_the_answer() -> bool:
    return 42 == 42  # [comparison-of-constants]

Correct code:

def is_the_answer(meaning_of_life: int) -> bool:
    return meaning_of_life == 42

Created by the basic checker.

  comparison-with-itself / R0124

Message emitted:

Redundant comparison - %s

Description:

Used when something is compared against itself.

Problematic code:

def is_an_orange(fruit):
    an_orange = "orange"
    return fruit == fruit  # [comparison-with-itself]

Correct code:

def is_an_orange(fruit):
    an_orange = "orange"
    return an_orange == fruit

Created by the basic checker.

  condition-evals-to-constant / R1727

Message emitted:

Boolean condition '%s' will always evaluate to '%s'

Description:

Emitted when a boolean condition can be simplified to a constant value.

Problematic code:

def is_a_fruit(fruit):
    return bool(fruit in {"apple", "orange"} or True)  # [condition-evals-to-constant]

Correct code:

def is_a_fruit(fruit):
    return fruit in {"apple", "orange"}

Created by the refactoring checker.

  confusing-consecutive-elif / R5601

Message emitted:

Consecutive elif with differing indentation level, consider creating a function to separate the inner elif

Description:

Used when an elif statement follows right after an indented block which itself ends with if or elif. It may not be ovious if the elif statement was willingly or mistakenly unindented. Extracting the indented if statement into a separate function might avoid confusion and prevent errors.

Problematic code:

def myfunc(shall_continue: bool, shall_exit: bool):
    if shall_continue:
        if input("Are you sure?") == "y":
            print("Moving on.")
    elif shall_exit:  # [confusing-consecutive-elif]
        print("Exiting.")

Correct code:

# Option 1: add explicit 'else'
def myfunc(shall_continue: bool, shall_exit: bool):
    if shall_continue:
        if input("Are you sure?") == "y":
            print("Moving on.")
        else:
            pass
    elif shall_exit:
        print("Exiting.")
# Option 2: extract function
def user_confirmation():
    if input("Are you sure?") == "y":
        print("Moving on.")
def myfunc2(shall_continue: bool, shall_exit: bool):
    if shall_continue:
        user_confirmation()
    elif shall_exit:
        print("Exiting.")

Configuration file:

[MAIN]
load-plugins=pylint.extensions.confusing_elif

Additional details:

Creating a function for the nested conditional, or adding an explicit else in the indented if statement, even if it only contains a pass statement, can help clarify the code.

NOTE:

This message is emitted by the optional 'confusing_elif'
    checker which requires the pylint.extensions.confusing_elif plugin to be loaded.

    Created by the confusing_elif checker.

  consider-alternative-union-syntax / R6003

Message emitted:

Consider using alternative Union syntax instead of '%s'%s

Description:

Emitted when 'typing.Union' or 'typing.Optional' is used instead of the alternative Union syntax 'int | None'.

Problematic code:

from typing import Union
cats: Union[int, str]  # [consider-alternative-union-syntax]

Correct code:

cats: (int | str)

Configuration file:

[MAIN]
load-plugins = pylint.extensions.typing

NOTE:

This message is emitted by the optional 'typing'
    checker which requires the pylint.extensions.typing plugin to be loaded.

    Created by the typing checker.

  consider-merging-isinstance / R1701

Message emitted:

Consider merging these isinstance calls to isinstance(%s, (%s))

Description:

Used when multiple consecutive isinstance calls can be merged into one.

Problematic code:

from typing import Any
def is_number(value: Any) -> bool:
    return isinstance(value, int) or isinstance(value, float)  # [consider-merging-isinstance]

Correct code:

from typing import Any
def is_number(value: Any) -> bool:
    return isinstance(value, (int, float))

Created by the refactoring checker.

  consider-refactoring-into-while-condition / R3501

Message emitted:

Consider using 'while %s' instead of 'while %s:' an 'if', and a 'break'

Description:

Emitted when `while True:` loop is used and the first statement is a break condition. The ``if / break`` construct can be removed if the check is inverted and moved to the ``while`` statement.

Problematic code:

fruit_basket = ["apple", "orange", "banana", "cherry", "guava"]
while True:  # [consider-refactoring-into-while-condition]
    if len(fruit_basket) == 0:
        break
    fruit = fruit_basket.pop()
    print(f"We removed {fruit} from the basket")

Correct code:

fruit_basket = ["apple", "orange", "banana", "cherry", "guava"]
while len(fruit_basket) != 0:
    fruit = fruit_basket.pop()
    print(f"We removed {fruit} from the basket")

Configuration file:

[MAIN]
load-plugins=pylint.extensions.consider_refactoring_into_while_condition

NOTE:

This message is emitted by the optional 'consider_refactoring_into_while'
    checker which requires the pylint.extensions.consider_refactoring_into_while_condition plugin to be loaded.

    Created by the consider_refactoring_into_while checker.

  consider-swap-variables / R1712

Message emitted:

Consider using tuple unpacking for swapping variables

Description:

You do not have to use a temporary variable in order to swap variables. Using "tuple unpacking" to directly swap variables makes the intention more clear.

Problematic code:

a = 1
b = 2
temp = a  # [consider-swap-variables]
a = b
b = temp

Correct code:

a = 1
b = 2
a, b = b, a

Created by the refactoring checker.

  consider-using-alias / R6002

Message emitted:

'%s' will be deprecated with PY39, consider using '%s' instead%s

Description:

Only emitted if 'runtime-typing=no' and a deprecated typing alias is used in a type annotation context in Python 3.7 or 3.8.

Problematic code:

import typing
cats: typing.Dict[str, int]  # [consider-using-alias]

Correct code:

import typing
cats: typing.cast(dict[str, int], "string")

Configuration file:

[main]
load-plugins = pylint.extensions.typing
py-version = 3.7
runtime-typing=no

NOTE:

This message is emitted by the optional 'typing'
    checker which requires the pylint.extensions.typing plugin to be loaded.

    Created by the typing checker.

  consider-using-assignment-expr / R6103

Message emitted:

Use '%s' instead

Description:

Emitted when an if assignment is directly followed by an if statement and both can be combined by using an assignment expression ``:=``. Requires Python 3.8 and ``py-version >= 3.8``.

Problematic code:

apples = 2
if apples:  # [consider-using-assignment-expr]
    print("God apples!")

Correct code:

if apples := 2:
    print("God apples!")

Configuration file:

[MAIN]
py-version=3.8
load-plugins=pylint.extensions.code_style

NOTE:

This message is emitted by the optional 'code_style'
    checker which requires the pylint.extensions.code_style plugin to be loaded.

    Created by the code_style checker.

  consider-using-augmented-assign / R6104

Message emitted:

Use '%s' to do an augmented assign directly

Description:

Emitted when an assignment is referring to the object that it is assigning to. This can be changed to be an augmented assign. Disabled by default!

CAUTION: This message is disabled by default. To enable it, add consider-using-augmented-assign to the enable option.

Problematic code:

x = 1
x = x + 1  # [consider-using-augmented-assign]

Correct code:

x = 1
x += 1

Configuration file:

[MAIN]
load-plugins=pylint.extensions.code_style
enable=consider-using-augmented-assign

NOTE:

This message is emitted by the optional 'code_style'
    checker which requires the pylint.extensions.code_style plugin to be loaded.

    Created by the code_style checker.

  consider-using-dict-comprehension / R1717

Message emitted:

Consider using a dictionary comprehension

Description:

Emitted when we detect the creation of a dictionary using the dict() callable and a transient list. Although there is nothing syntactically wrong with this code, it is hard to read and can be simplified to a dict comprehension. Also it is faster since you don't need to create another transient list

Problematic code:

NUMBERS = [1, 2, 3]
# +1: [consider-using-dict-comprehension]
DOUBLED_NUMBERS = dict([(number, number * 2) for number in NUMBERS])

Correct code:

NUMBERS = [1, 2, 3]
DOUBLED_NUMBERS = {number: number * 2 for number in NUMBERS}

Additional details:

pyupgrade can fix this issue automatically.

Created by the refactoring checker.

  consider-using-from-import / R0402

Message emitted:

Use 'from %s import %s' instead

Description:

Emitted when a submodule of a package is imported and aliased with the same name, e.g., instead of ``import concurrent.futures as futures`` use ``from concurrent import futures``.

Problematic code:

import os.path as path  # [consider-using-from-import]

Correct code:

from os import path

Created by the imports checker.

  consider-using-generator / R1728

Message emitted:

Consider using a generator instead '%s(%s)'

Description:

If your container can be large using a generator will bring better performance.

Problematic code:

list([0 for y in list(range(10))])  # [consider-using-generator]
tuple([0 for y in list(range(10))])  # [consider-using-generator]
sum([y**2 for y in list(range(10))])  # [consider-using-generator]
max([y**2 for y in list(range(10))])  # [consider-using-generator]
min([y**2 for y in list(range(10))])  # [consider-using-generator]

Correct code:

list(0 for y in list(range(10)))
tuple(0 for y in list(range(10)))
sum(y**2 for y in list(range(10)))
max(y**2 for y in list(range(10)))
min(y**2 for y in list(range(10)))

Additional details:

Removing [] inside calls that can use containers or generators should be considered for performance reasons since a generator will have an upfront cost to pay. The performance will be better if you are working with long lists or sets.

For max, min and sum using a generator is also recommended by pep289.

Related links:

•   PEP 289

•   Benchmark and discussion for any/all/list/tuple

•   Benchmark and discussion for sum/max/min

    Created by the refactoring checker.

  consider-using-get / R1715

Message emitted:

Consider using dict.get for getting values from a dict if a key is present or a default if not

Description:

Using the builtin dict.get for getting a value from a dictionary if a key is present or a default if not, is simpler and considered more idiomatic, although sometimes a bit slower

Problematic code:

knights = {"Gallahad": "the pure", "Robin": "the brave"}
if "Gallahad" in knights:  # [consider-using-get]
    DESCRIPTION = knights["Gallahad"]
else:
    DESCRIPTION = ""

Correct code:

knights = {"Gallahad": "the pure", "Robin": "the brave"}
description = knights.get("Gallahad", "")

Created by the refactoring checker.

  consider-using-in / R1714

Message emitted:

Consider merging these comparisons with 'in' by using '%s %sin (%s)'. Use a set instead if elements are hashable.

Description:

To check if a variable is equal to one of many values, combine the values into a set or tuple and check if the variable is contained "in" it instead of checking for equality against each of the values. This is faster and less verbose.

Problematic code:

def fruit_is_round(fruit):
    return fruit == "apple" or fruit == "orange" or fruit == "melon"  # [consider-using-in]

Correct code:

def fruit_is_round(fruit):
    return fruit in {"apple", "orange", "melon"}

Created by the refactoring checker.

  consider-using-join / R1713

Message emitted:

Consider using str.join(sequence) for concatenating strings from an iterable

Description:

Using str.join(sequence) is faster, uses less memory and increases readability compared to for-loop iteration.

Problematic code:

def fruits_to_string(fruits):
    formatted_fruit = ""
    for fruit in fruits:
        formatted_fruit += fruit  # [consider-using-join]
    return formatted_fruit
print(fruits_to_string(["apple", "pear", "peach"]))

Correct code:

print("".join(["apple", "pear", "peach"]))

Created by the refactoring checker.

  consider-using-max-builtin / R1731

Message emitted:

Consider using '%s' instead of unnecessary if block

Description:

Using the max builtin instead of a conditional improves readability and conciseness.

Problematic code:

def get_max(value1, value2):
    if value1 < value2:  # [consider-using-max-builtin]
        value1 = value2
    return value1
print(get_max(1, 2))

Correct code:

print(max(1, 2))

Created by the refactoring checker.

  consider-using-min-builtin / R1730

Message emitted:

Consider using '%s' instead of unnecessary if block

Description:

Using the min builtin instead of a conditional improves readability and conciseness.

Problematic code:

def get_min(value1, value2):
    if value1 > value2:  # [consider-using-min-builtin]
        value1 = value2
    return value1
print(get_min(1, 2))

Correct code:

print(min(1, 2))

Created by the refactoring checker.

  consider-using-namedtuple-or-dataclass / R6101

Message emitted:

Consider using namedtuple or dataclass for dictionary values

Description:

Emitted when dictionary values can be replaced by namedtuples or dataclass instances.

Problematic code:

FELIDAES = {  # [consider-using-namedtuple-or-dataclass]
    "The queen's cymric, fragile furry friend": {
        "tail_length_cm": 1,
        "paws": 4,
        "eyes": 2,
        "Elizabethan collar": 1,
    },
    "Rackat the red, terror of the sea": {
        "tail_length_cm": 13,
        "paws": 3,
        "eyes": 1,
        "Red Hat": 1,
    },
}

Correct code:

from typing import NamedTuple
class FelidaeCharacteristics(NamedTuple):
    tail_length_cm: int
    paws: int
    eyes: int
    hat: str | None
FELIDAES = {
    "The queen's cymric, fragile furry friend": FelidaeCharacteristics(
        tail_length_cm=1, paws=4, eyes=2, hat="Elizabethan collar"
    ),
    "Rackat the red, terror of the sea": FelidaeCharacteristics(
        tail_length_cm=21, paws=3, eyes=1, hat="Red Hat"
    ),
}

Configuration file:

[MAIN]
load-plugins=pylint.extensions.code_style

NOTE:

This message is emitted by the optional 'code_style'
    checker which requires the pylint.extensions.code_style plugin to be loaded.

    Created by the code_style checker.

  consider-using-set-comprehension / R1718

Message emitted:

Consider using a set comprehension

Description:

Although there is nothing syntactically wrong with this code, it is hard to read and can be simplified to a set comprehension. Also it is faster since you don't need to create another transient list

Problematic code:

NUMBERS = [1, 2, 2, 3, 4, 4]
# +1: [consider-using-set-comprehension]
UNIQUE_EVEN_NUMBERS = set([number for number in NUMBERS if number % 2 == 0])

Correct code:

NUMBERS = [1, 2, 2, 3, 4, 4]
UNIQUE_EVEN_NUMBERS = {number for number in NUMBERS if number % 2 == 0}

Additional details:

pyupgrade can fix this issue automatically.

Created by the refactoring checker.

  consider-using-sys-exit / R1722

Message emitted:

Consider using 'sys.exit' instead

Description:

Contrary to 'exit()' or 'quit()', 'sys.exit' does not rely on the site module being available (as the 'sys' module is always available).

Problematic code:

if __name__ == "__main__":
    user = input("Enter user name: ")
    print(f"Hello, {user}")
    exit(0)  # [consider-using-sys-exit]

Correct code:

import sys
if __name__ == "__main__":
    user = input("Enter user name: ")
    print(f"Hello, {user}")
    sys.exit(0)

Created by the refactoring checker.

  consider-using-ternary / R1706

Message emitted:

Consider using ternary (%s)

Description:

Used when one of known pre-python 2.5 ternary syntax is used.

Problematic code:

x, y = 1, 2
maximum = x >= y and x or y  # [consider-using-ternary]

Correct code:

x, y = 1, 2
maximum = x if x >= y else y

Created by the refactoring checker.

  consider-using-tuple / R6102

Message emitted:

Consider using an in-place tuple instead of list

Description:

Only for style consistency! Emitted where an in-place defined ``list`` can be replaced by a ``tuple``. Due to optimizations by CPython, there is no performance benefit from it.

Problematic code:

for i in [1, 2, 3]:  # [consider-using-tuple]
    print(i)

Correct code:

for i in (1, 2, 3):
    print(i)

Configuration file:

[MAIN]
load-plugins=pylint.extensions.code_style

NOTE:

This message is emitted by the optional 'code_style'
    checker which requires the pylint.extensions.code_style plugin to be loaded.

    Created by the code_style checker.

  consider-using-with / R1732

Message emitted:

Consider using 'with' for resource-allocating operations

Description:

Emitted if a resource-allocating assignment or call may be replaced by a 'with' block. By using 'with' the release of the allocated resources is ensured even in the case of an exception.

Problematic code:

file = open("apple.txt", "r", encoding="utf8")  # [consider-using-with]
contents = file.read()
file.close()
worst = open("banana.txt", "r", encoding="utf8").read()  # [consider-using-with]

Correct code:

with open("apple.txt", "r", encoding="utf8") as file:
    contents = file.read()
with open("banana.txt", "r", encoding="utf8") as f:
    best = f.read()

Additional details:

Calling write() without using the with keyword or calling close() might result in the arguments of write() not being completely written to the disk, even if the program exits successfully.

This message applies to callables of Python's stdlib which can be replaced by a with statement. It is suppressed in the following cases:

•   the call is located inside a context manager

•   the call result is returned from the enclosing function

•   the call result is used in a with statement itself

    Related links:

•   Python doc: Reading and writing files

•   PEP 343

•   Context managers in Python by John Lekberg

•   Rationale

    Created by the refactoring checker.

  cyclic-import / R0401

Message emitted:

Cyclic import (%s)

Description:

Used when a cyclic import between two or more modules is detected.

Correct code:

# This is a placeholder for correct code for this message.

Additional details:

You can help us make the doc better by contributing !

Created by the imports checker.

  duplicate-code / R0801

Message emitted:

Similar lines in %s files %s

Description:

Indicates that a set of similar lines has been detected among multiple file. This usually means that the code should be refactored to avoid this duplication.

Problematic code:

apple.py:

class Apple:
    def __init__(self):
        self.remaining_bites = 3
    def take_bite(self):
        if self.remaining_bites > 0:
            print("You take a bite of the apple.")
            self.remaining_bites -= 1
        else:
            print("The apple is already eaten up!")
    def eaten_by_animal(self, animal):
        self.remaining_bites = 0
        print("The apple has been eaten by an animal.")

orange.py:

class Orange: # [duplicate-code]
    def __init__(self):
        self.remaining_bites = 3
    def take_bite(self):
        if self.remaining_bites > 0:
            print("You take a bite of the apple.")
            self.remaining_bites -= 1
        else:
            print("The orange is already eaten up!")
    def eaten_by_animal(self, animal):
        if animal == "cat":
            raise ValueError("A cat would never do that !")
        self.remaining_bites = 0
        print("The orange has been eaten by an animal.")

Correct code:

apple.py:

from fruit import Fruit
class Apple(Fruit):
    ...

fruit.py:

class Fruit:
    def __init__(self):
        self.remaining_bites = 3
    def take_bite(self):
        if self.remaining_bites > 0:
            print(f"You take a bite of the {self.__class__.__name__.lower()}.")
            self.remaining_bites -= 1
        else:
            print(f"The {self.__class__.__name__.lower()} is already eaten up!")
    def eaten_by_animal(self, animal):
        self.remaining_bites = 0
        print(f"The {self.__class__.__name__.lower()} has been eaten by an animal.")

orange.py:

from fruit import Fruit
class Orange(Fruit):
    def eaten_by_animal(self, animal):
        if animal == "cat":
            raise ValueError("A cat would never do that !")
        super().eaten_by_animal(animal)

Additional details:

If you need to make a change to the logic or functionality of the duplicated code, you will need to identify all the places that need to be changed, which can be time-consuming and error-prone. If there are multiple copies of the same code, then you will also need to test each copy to ensure that the functionality is correct. Duplicate code can be confusing for someone who is trying to understand the logic and flow of the code if they come across multiple identical or nearly identical blocks of code. The reader can then skim and think something is identical when it actually isn't. This is particularly true during review.

Created by the similarities checker.

  else-if-used / R5501

Message emitted:

Consider using "elif" instead of "else" then "if" to remove one indentation level

Description:

Used when an else statement is immediately followed by an if statement and does not contain statements that would be unrelated to it.

Problematic code:

if input():
    pass
else:
    if len(input()) >= 10:  # [else-if-used]
        pass
    else:
        pass

Correct code:

if input():
    pass
elif len(input()) >= 10:
    pass
else:
    pass

Configuration file:

[MAIN]
load-plugins=pylint.extensions.check_elif

NOTE:

This message is emitted by the optional 'else_if_used'
    checker which requires the pylint.extensions.check_elif plugin to be loaded.

    Created by the else_if_used checker.

  empty-comment / R2044

Message emitted:

Line with empty comment

Description:

Used when a # symbol appears on a line not followed by an actual comment

Problematic code:

# +1:[empty-comment]
#
# +1:[empty-comment]
x = 0  #

Correct code:

# comment
x = 0  # comment

Configuration file:

[main]
load-plugins=pylint.extensions.empty_comment

NOTE:

This message is emitted by the optional 'empty-comment'
    checker which requires the pylint.extensions.empty_comment plugin to be loaded.

    Created by the empty-comment checker.

  inconsistent-return-statements / R1710

Message emitted:

Either all return statements in a function should return an expression, or none of them should.

Description:

According to PEP8, if any return statement returns an expression, any return statements where no value is returned should explicitly state this as return None, and an explicit return statement should be present at the end of the function (if reachable)

Problematic code:

def get_the_answer(value: str) -> str | None:  # [inconsistent-return-statements]
    if value:
        return value

Correct code:

def get_the_answer(value: str) -> str | None:
    if value:
        return value
    return None

Created by the refactoring checker.

  literal-comparison / R0123

Message emitted:

In '%s', use '%s' when comparing constant literals not '%s' ('%s')

Description:

Used when comparing an object to a literal, which is usually what you do not want to do, since you can compare to a different literal than what was expected altogether.

Problematic code:

def is_an_orange(fruit):
    return fruit is "orange"  # [literal-comparison]

Correct code:

def is_an_orange(fruit):
    return fruit == "orange"

Related links:

•   Comparison operations in Python

    Created by the basic checker.

  magic-value-comparison / R2004

Message emitted:

Consider using a named constant or an enum instead of '%s'.

Description:

Using named constants instead of magic values helps improve readability and maintainability of your code, try to avoid them in comparisons.

Problematic code:

import random
measurement = random.randint(0, 200)
above_threshold = False
i = 0
while i < 5:   # [magic-value-comparison]
    above_threshold = measurement > 100   # [magic-value-comparison]
    if above_threshold:
        break
    measurement = random.randint(0, 200)

Correct code:

import random
MAX_NUM_OF_ITERATIONS = 5
THRESHOLD_VAL = 100
MIN_MEASUREMENT_VAL = 0
MAX_MEASUREMENT_VAL = 200
measurement = random.randint(MIN_MEASUREMENT_VAL, MAX_MEASUREMENT_VAL)
above_threshold = False
i = 0
while i < MAX_NUM_OF_ITERATIONS:
    above_threshold = measurement > THRESHOLD_VAL
    if above_threshold:
        break
    measurement = random.randint(MIN_MEASUREMENT_VAL, MAX_MEASUREMENT_VAL)

Configuration file:

[main]
load-plugins=pylint.extensions.magic_value

NOTE:

This message is emitted by the optional 'magic-value'
    checker which requires the pylint.extensions.magic_value plugin to be loaded.

    Created by the magic-value checker.

  no-classmethod-decorator / R0202

Message emitted:

Consider using a decorator instead of calling classmethod

Description:

Used when a class method is defined without using the decorator syntax.

Problematic code:

class Fruit:
    COLORS = []
    def __init__(self, color):
        self.color = color
    def pick_colors(cls, *args):
        """classmethod to pick fruit colors"""
        cls.COLORS = args
    pick_colors = classmethod(pick_colors)  # [no-classmethod-decorator]

Correct code:

class Fruit:
    COLORS = []
    def __init__(self, color):
        self.color = color
    @classmethod
    def pick_colors(cls, *args):
        """classmethod to pick fruit colors"""
        cls.COLORS = args

Created by the classes checker.

  no-else-break / R1723

Message emitted:

Unnecessary "%s" after "break", %s

Description:

Used in order to highlight an unnecessary block of code following an if containing a break statement. As such, it will warn when it encounters an else following a chain of ifs, all of them containing a break statement.

Problematic code:

def next_seven_elements(iterator):
    for i, item in enumerate(iterator):
        if i == 7:  # [no-else-break]
            break
        else:
            yield item

Correct code:

def next_seven_elements(iterator):
    for i, item in enumerate(iterator):
        if i == 7:
            break
        yield item

Created by the refactoring checker.

  no-else-continue / R1724

Message emitted:

Unnecessary "%s" after "continue", %s

Description:

Used in order to highlight an unnecessary block of code following an if containing a continue statement. As such, it will warn when it encounters an else following a chain of ifs, all of them containing a continue statement.

Problematic code:

def even_number_under(n: int):
    for i in range(n):
        if i%2 == 1:  # [no-else-continue]
            continue
        else:
            yield i

Correct code:

def even_number_under(n: int):
    for i in range(n):
        if i%2 == 1:
            continue
        yield i

Created by the refactoring checker.

  no-else-raise / R1720

Message emitted:

Unnecessary "%s" after "raise", %s

Description:

Used in order to highlight an unnecessary block of code following an if containing a raise statement. As such, it will warn when it encounters an else following a chain of ifs, all of them containing a raise statement.

Problematic code:

def integer_sum(a: int, b: int) -> int:
    if not (isinstance(a, int) and isinstance(b, int)):    # [no-else-raise]
        raise ValueError('Function supports only integer parameters.')
    else:
        return a + b

Correct code:

def integer_sum(a: int, b: int) -> int:
    if not (isinstance(a, int) and isinstance(b, int)):
        raise ValueError('Function supports only integer parameters.')
    return a + b

Created by the refactoring checker.

  no-else-return / R1705

Message emitted:

Unnecessary "%s" after "return", %s

Description:

Used in order to highlight an unnecessary block of code following an if containing a return statement. As such, it will warn when it encounters an else following a chain of ifs, all of them containing a return statement.

Problematic code:

def compare_numbers(a: int, b: int) -> int:
    if a == b:  # [no-else-return]
        return 0
    elif a < b:
        return -1
    else:
        return 1

Correct code:

def compare_numbers(a: int, b: int) -> int:
    if a == b:
        return 0
    if a < b:
        return -1
    return 1

Created by the refactoring checker.

  no-self-use / R6301

Message emitted:

Method could be a function

Description:

Used when a method doesn't use its bound instance, and so could be written as a function.

Problematic code:

class Person:
    def developer_greeting(self):  # [no-self-use]
        print("Greetings developer!")
    def greeting_1(self):  # [no-self-use]
        print("Hello!")
    def greeting_2(self):  # [no-self-use]
        print("Hi!")

Correct code:

def developer_greeting():
    print("Greetings developer!")
class Person:
    name = "Paris"
    def greeting_1(self):
        print(f"Hello from {self.name} !")
    @staticmethod
    def greeting_2():
        print("Hi!")

Configuration file:

[MAIN]
load-plugins=pylint.extensions.no_self_use,

Additional details:

If a function is not using any class attribute it can be a @staticmethod, or a function outside the class.

NOTE:

This message is emitted by the optional 'no_self_use'
    checker which requires the pylint.extensions.no_self_use plugin to be loaded.

    Created by the no_self_use checker.

  no-staticmethod-decorator / R0203

Message emitted:

Consider using a decorator instead of calling staticmethod

Description:

Used when a static method is defined without using the decorator syntax.

Problematic code:

class Worm:
    def bore(self):
        pass
    bore = staticmethod(bore)  # [no-staticmethod-decorator]

Correct code:

class Worm:
    @staticmethod
    def bore(self):
        pass

Created by the classes checker.

  property-with-parameters / R0206

Message emitted:

Cannot have defined parameters for properties

Description:

Used when we detect that a property also has parameters, which are useless, given that properties cannot be called with additional arguments.

Problematic code:

class Worm:
    @property
    def bore(self, depth):  # [property-with-parameters]
        pass

Correct code:

class Worm:
    @property
    def bore(self):
        """Property accessed with '.bore'."""
        pass
    def bore_with_depth(depth):
        """Function called with .bore_with_depth(depth)."""
        pass

Created by the classes checker.

  redefined-argument-from-local / R1704

Message emitted:

Redefining argument with the local name %r

Description:

Used when a local name is redefining an argument, which might suggest a potential error. This is taken in account only for a handful of name binding operations, such as for iteration, with statement assignment and exception handler assignment.

Problematic code:

def show(host_id=10.11):
    for host_id, host in [[12.13, 'Venus'], [14.15, 'Mars']]:  # [redefined-argument-from-local]
        print(host_id, host)

Correct code:

def show(host_id=10.11):
    for inner_host_id, host in [[12.13, 'Venus'], [14.15, 'Mars']]:
        print(host_id, inner_host_id, host)

Created by the refactoring checker.

  redefined-variable-type / R0204

Message emitted:

Redefinition of %s type from %s to %s

Description:

Used when the type of a variable changes inside a method or a function.

Problematic code:

x = 1
x = "2"  # [redefined-variable-type]

Correct code:

x = 1
x = 2

Configuration file:

[MAIN]
load-plugins=pylint.extensions.redefined_variable_type,

NOTE:

This message is emitted by the optional 'multiple_types'
    checker which requires the pylint.extensions.redefined_variable_type plugin to be loaded.

    Created by the multiple_types checker.

  redundant-typehint-argument / R6006

Message emitted:

Type `%s` is used more than once in union type annotation. Remove redundant typehints.

Description:

Duplicated type arguments will be skipped by `mypy` tool, therefore should be removed to avoid confusion.

Problematic code:

from typing import Union
sweet_count: Union[int, str, int] = 42  # [redundant-typehint-argument]

Correct code:

from typing import Union
sweet_count: Union[str, int] = 42

Configuration file:

[main]
load-plugins=pylint.extensions.typing
[testoptions]
min_pyver=3.7

NOTE:

This message is emitted by the optional 'typing'
    checker which requires the pylint.extensions.typing plugin to be loaded.

    Created by the typing checker.

  simplifiable-condition / R1726

Message emitted:

Boolean condition '%s' may be simplified to '%s'

Description:

Emitted when a boolean condition is able to be simplified.

Problematic code:

def has_apples(apples) -> bool:
    return bool(apples or False)  # [simplifiable-condition]

Correct code:

def has_apples(apples) -> bool:
    return bool(apples)

Created by the refactoring checker.

  simplifiable-if-expression / R1719

Message emitted:

The if expression can be replaced with %s

Description:

Used when an if expression can be replaced with 'bool(test)' or simply 'test' if the boolean cast is implicit.

Problematic code:

FLYING_THINGS = ["bird", "plane", "superman", "this example"]
def is_flying_thing(an_object):
    return True if an_object in FLYING_THINGS else False  # [simplifiable-if-expression]
def is_not_flying_thing(an_object):
    return False if an_object in FLYING_THINGS else True  # [simplifiable-if-expression]

Correct code:

FLYING_THINGS = ["bird", "plane", "superman", "this example"]
def is_flying_thing(an_object):
    return an_object in FLYING_THINGS
def is_not_flying_thing(an_object):
    return an_object not in FLYING_THINGS

Related links:

•   Simplifying an 'if' statement with bool()

    Created by the refactoring checker.

  simplifiable-if-statement / R1703

Message emitted:

The if statement can be replaced with %s

Description:

Used when an if statement can be replaced with 'bool(test)'.

Problematic code:

FLYING_THINGS = ["bird", "plane", "superman", "this example"]
def is_flying_animal(an_object):
    if isinstance(an_object, Animal) and an_object in FLYING_THINGS:  # [simplifiable-if-statement]
        is_flying = True
    else:
        is_flying = False
    return is_flying

Correct code:

FLYING_THINGS = ["bird", "plane", "superman", "this example"]
def is_flying_animal(an_object):
    is_flying = isinstance(an_object, Animal) and an_object.name in FLYING_THINGS
    return is_flying

Created by the refactoring checker.

  simplify-boolean-expression / R1709

Message emitted:

Boolean expression may be simplified to %s

Description:

Emitted when redundant pre-python 2.5 ternary syntax is used.

Problematic code:

def has_oranges(oranges, apples=None) -> bool:
    return apples and False or oranges  # [simplify-boolean-expression]

Correct code:

def has_oranges(oranges, apples=None) -> bool:
    return oranges

Created by the refactoring checker.

  stop-iteration-return / R1708

Message emitted:

Do not raise StopIteration in generator, use return statement instead

Description:

According to PEP479, the raise of StopIteration to end the loop of a generator may lead to hard to find bugs. This PEP specify that raise StopIteration has to be replaced by a simple return statement

Problematic code:

def fruit_generator():
    for fruit in ["apple", "banana"]:
        yield fruit
    raise StopIteration  # [stop-iteration-return]
def two_fruits_generator(fruits):
    for fruit in fruits:
        yield fruit, next(fruits)  # [stop-iteration-return]
def two_good_fruits_generator(fruits):
    for fruit in fruits:
        if not fruit.is_tasty():
            continue
        while True:
            next_fruit = next(fruits)  # [stop-iteration-return]
            if next_fruit.is_tasty():
                yield fruit, next_fruit
                break

Correct code:

def fruit_generator():
    """The example is simple enough you don't need an explicit return."""
    for fruit in ["apple", "banana"]:
        yield fruit
def two_fruits_generator(fruits):
    """Catching the StopIteration."""
    for fruit in fruits:
        try:
            yield fruit, next(fruits)
        except StopIteration:
            print("Sorry there is only one fruit left.")
            yield fruit, None
def two_good_fruits_generator(fruits):
    """A return can be used to end the iterator early, but not a StopIteration."""
    for fruit in fruits:
        if not fruit.is_tasty():
            continue
        while True:
            next_fruit = next(fruits, None)
            if next_fruit is None:
                print("Sorry there is only one fruit left.")
                yield fruit, None
                # We reached the end of the 'fruits' generator but raising a
                # StopIteration instead of returning would create a RuntimeError
                return
            if next_fruit.is_tasty():
                yield fruit, next_fruit
                break

Additional details:

It's possible to give a default value to next or catch the StopIteration, or return directly. A StopIteration cannot be propagated from a generator.

Related links:

•   PEP 479

    Created by the refactoring checker.

  super-with-arguments / R1725

Message emitted:

Consider using Python 3 style super() without arguments

Description:

Emitted when calling the super() builtin with the current class and instance. On Python 3 these arguments are the default and they can be omitted.

Problematic code:

class Fruit:
    pass
class Orange(Fruit):
    def __init__(self):
        super(Orange, self).__init__()  # [super-with-arguments]

Correct code:

class Fruit:
    pass
class Orange(Fruit):
    def __init__(self):
        super().__init__()

Created by the refactoring checker.

  too-complex / R1260

Message emitted:

%s is too complex. The McCabe rating is %d

Description:

Used when a method or function is too complex based on McCabe Complexity Cyclomatic

Problematic code:

def fifty_percent_off(whole):
    return (float(whole)) * 50 / 100
def calculate_sum_and_display_price_of_fruits(*fruits):  # [too-complex]
    # McCabe rating is 13 here (by default 10)
    shopping_list = []
    if "apple" in fruits:
        v = fifty_percent_off(1.1)
        shopping_list.append(v)
    if "pear" in fruits:
        shopping_list.append(0.8)
    if "banana" in fruits:
        shopping_list.append(1.2)
    if "mango" in fruits:
        shopping_list.append(3.5)
    if "peach" in fruits:
        shopping_list.append(0.5)
    if "melon" in fruits:
        shopping_list.append(4.9)
    if "orange" in fruits:
        shopping_list.append(2.0)
    if "strawberry" in fruits:
        shopping_list.append(2.5)
    if "mandarin" in fruits:
        shopping_list.append(2.3)
    if "plum" in fruits:
        shopping_list.append(0.5)
    if "watermelon" in fruits:
        v = fifty_percent_off(6.4)
        shopping_list.append(v)
    combine = zip(fruits, shopping_list)
    for i in combine:
        print(f"{i[0]} ${i[1]:.2f}")
    total = sum(shopping_list)
    print(f"Total price is ${total:.2f}")
fruits_to_buy = ["apple", "orange", "watermelon"]
calculate_sum_and_display_price_of_fruits(*fruits_to_buy)

Correct code:

FRUIT_PRICES = {
    "apple": 1.1,
    "pear": 0.8,
    "banana": 1.2,
    "mango": 3.5,
    "peach": 0.5,
    "melon": 4.9,
    "orange": 2.0,
    "strawberry": 2.5,
    "mandarin": 2.3,
    "plum": 0.5,
    "watermelon": 6.4,
}
DISCOUNTED_FRUITS = ["apple", "watermelon"]
def fifty_percent_off(whole):
    return (float(whole)) * 50 / 100
def get_price(fruit):
    full_price = FRUIT_PRICES.get(fruit)
    if fruit in DISCOUNTED_FRUITS:
        return fifty_percent_off(full_price)
    else:
        return full_price
def display_fruit_and_price(fruits):
    for fruit in fruits:
        print(f"{fruit} ${get_price(fruit) :.2f}")
def get_total(fruits):
    return sum(get_price(f) for f in fruits)
fruits_to_buy = ["apple", "orange", "watermelon"]
display_fruit_and_price(fruits_to_buy)
print(f"Total price is ${get_total(fruits_to_buy):.2f}")

Configuration file:

[main]
load-plugins=pylint.extensions.mccabe

NOTE:

This message is emitted by the optional 'design'
    checker which requires the pylint.extensions.mccabe plugin to be loaded.

    Created by the design checker.

  too-few-public-methods / R0903

Message emitted:

Too few public methods (%s/%s)

Description:

Used when class has too few public methods, so be sure it's really worth it.

Problematic code:

class Worm:  # [too-few-public-methods]
    def __init__(self, name: str, fruit_of_residence: Fruit):
        self.name = name
        self.fruit_of_residence = fruit_of_residence
    def bore(self):
        print(f"{self.name} is boring into {self.fruit_of_residence}")

Correct code:

import dataclasses
class Worm:
    def __init__(self, name: str, fruit_of_residence: Fruit):
        self.name = name
        self.fruit_of_residence = fruit_of_residence
    def bore(self):
        print(f"{self.name} is boring into {self.fruit_of_residence}")
    def wiggle(self):
        print(f"{self.name} wiggle around wormily.")
# or
@dataclasses.dataclass
class Worm:
    name:str
    fruit_of_residence: Fruit
def bore(worm: Worm):
    print(f"{worm.name} is boring into {worm.fruit_of_residence}")
# or
def bore(fruit: Fruit, worm_name: str):
    print(f"{worm_name} is boring into {fruit}")

Created by the design checker.

  too-many-ancestors / R0901

Message emitted:

Too many ancestors (%s/%s)

Description:

Used when class has too many parent classes, try to reduce this to get a simpler (and so easier to use) class.

Problematic code:

class Animal: ...
class BeakyAnimal(Animal): ...
class FurryAnimal(Animal): ...
class Swimmer(Animal): ...
class EggLayer(Animal): ...
class VenomousAnimal(Animal): ...
class ProtectedSpecie(Animal): ...
class BeaverTailedAnimal(Animal): ...
class Vertebrate(Animal): ...
# max of 7 by default, can be configured
# each edge of a diamond inheritance counts
class Playtypus(  # [too-many-ancestors]
    BeakyAnimal,
    FurryAnimal,
    Swimmer,
    EggLayer,
    VenomousAnimal,
    ProtectedSpecie,
    BeaverTailedAnimal,
    Vertebrate,
):
    pass

Correct code:

class Animal:
    beaver_tailed: bool
    can_swim: bool
    has_beak: bool
    has_fur: bool
    has_vertebrae: bool
    lays_egg: bool
    protected_specie: bool
    venomous: bool
class Invertebrate(Animal):
    has_vertebrae = False
class Vertebrate(Animal):
    has_vertebrae = True
class Mammal(Vertebrate):
    has_beak = False
    has_fur = True
    lays_egg = False
    venomous = False
class Playtypus(Mammal):
    beaver_tailed = True
    can_swim = True
    has_beak = True
    lays_egg = False
    protected_specie = True
    venomous = True

Created by the design checker.

  too-many-arguments / R0913

Message emitted:

Too many arguments (%s/%s)

Description:

Used when a function or method takes too many arguments.

Problematic code:

def three_d_chess_move(  # [too-many-arguments]
    x_white,
    y_white,
    z_white,
    piece_white,
    x_black,
    y_black,
    z_black,
    piece_black,
    x_blue,
    y_blue,
    z_blue,
    piece_blue,
    current_player,
):
    pass

Correct code:

from dataclasses import dataclass
@dataclass
class ThreeDChessPiece:
    x: int
    y: int
    z: int
    type: str
def three_d_chess_move(
    white: ThreeDChessPiece,
    black: ThreeDChessPiece,
    blue: ThreeDChessPiece,
    current_player,
):
    pass

Created by the design checker.

  too-many-boolean-expressions / R0916

Message emitted:

Too many boolean expressions in if statement (%s/%s)

Description:

Used when an if statement contains too many boolean expressions.

Problematic code:

def can_be_divided_by_two_and_are_not_zero(x, y, z):
    # Maximum number of boolean expressions in an if statement (by default 5)
    # +1: [too-many-boolean-expressions]
    if (x and y and z) and (x % 2 == 0 and y % 2 == 0 and z % 2 == 0):
        pass

Correct code:

def can_be_divided_by_two_and_are_not_zero(x, y, z):
    if all(i and i%2==0 for i in [x, y, z]):
        pass

Created by the design checker.

  too-many-branches / R0912

Message emitted:

Too many branches (%s/%s)

Description:

Used when a function or method has too many branches, making it hard to follow.

Problematic code:

def num_to_word(x):  # [too-many-branches]
    if x == 0:
        return "zero"
    elif x == 1:
        return "one"
    elif x == 2:
        return "two"
    elif x == 3:
        return "three"
    elif x == 4:
        return "four"
    elif x == 5:
        return "five"
    elif x == 6:
        return "six"
    elif x == 7:
        return "seven"
    elif x == 8:
        return "eight"
    elif x == 9:
        return "nine"
    else:
        return None

Correct code:

def num_to_word(x):
    return {
        0: "zero",
        1: "one",
        2: "two",
        3: "three",
        4: "for",
        5: "fie",
        6: "six",
        7: "seven",
        8: "eight",
        9: "nine",
    }.get(x)

Configuration file:

[main]
max-branches=10

Created by the design checker.

  too-many-instance-attributes / R0902

Message emitted:

Too many instance attributes (%s/%s)

Description:

Used when class has too many instance attributes, try to reduce this to get a simpler (and so easier to use) class.

Problematic code:

class Fruit:  # [too-many-instance-attributes]
    def __init__(self):
        # max of 7 attributes by default, can be configured
        self.worm_name = "Jimmy"
        self.worm_type = "Codling Moths"
        self.worm_color = "light brown"
        self.fruit_name = "Little Apple"
        self.fruit_color = "Bright red"
        self.fruit_vitamins = ["A", "B1"]
        self.fruit_antioxidants = None
        self.secondary_worm_name = "Kim"
        self.secondary_worm_type = "Apple maggot"
        self.secondary_worm_color = "Whitish"

Correct code:

import dataclasses
@dataclasses.dataclass
class Worm:
    name: str
    type: str
    color: str
class Fruit:
    def __init__(self):
        self.name = "Little Apple"
        self.color = "Bright red"
        self.vitamins = ["A", "B1"]
        self.antioxidants = None
        self.worms = [
            Worm(name="Jimmy", type="Codling Moths", color="light brown"),
            Worm(name="Kim", type="Apple maggot", color="Whitish"),
        ]

Created by the design checker.

  too-many-locals / R0914

Message emitted:

Too many local variables (%s/%s)

Description:

Used when a function or method has too many local variables.

Problematic code:

from childhood import Child, Sweet
def handle_sweets(infos):  # [too-many-locals]
    # Create children
    children = [Child(info) for info in infos]
    number_of_sweets = 87
    sweets = [Sweet() * number_of_sweets]
    number_of_sweet_per_child = 5
    money = 45.0
    sweets_given = 0
    time_to_eat_sweet = 54
    price_of_sweet = 0.42
    # distribute sweet
    for child in children:
        sweets_given += number_of_sweet_per_child
        child.give(sweets[number_of_sweet_per_child:])
    # calculate prices
    cost_of_children = sweets_given * price_of_sweet
    # Calculate remaining money
    remaining_money = money - cost_of_children
    # Calculate time it took
    time_it_took_assuming_parallel_eating = time_to_eat_sweet * number_of_sweet_per_child
    print(
        f"{children} ate {cost_of_children}¤ of sweets in {time_it_took_assuming_parallel_eating}, "
        f"you still have {remaining_money}"
    )

Correct code:

from typing import NamedTuple
from childhood import Child, Sweet
class SweetDistrubutionCharacteristics(NamedTuple):
    number_of_sweets: int
    number_of_sweet_per_child: int
    number_of_children: int
    @property
    def sweets_given(self):
        return self.number_of_sweet_per_child * self.number_of_children
def handle_sweets(infos):
    children = [Child(info) for info in infos]
    characteristics = SweetDistrubutionCharacteristics(87, 5, len(children))
    _allocate_sweets_to_children(children, characteristics)
    financial_impact = _assess_financial_impact(characteristics)
    print(f"{children} ate {financial_impact}")
def _allocate_sweets_to_children(
    children, characteristics: SweetDistrubutionCharacteristics
) -> None:
    sweets = [Sweet() * characteristics.number_of_sweets]
    for child in children:
        child.give(sweets[characteristics.number_of_sweet_per_child :])
def _assess_financial_impact(characteristics: SweetDistrubutionCharacteristics) -> str:
    time_to_eat_sweet = 54
    money = 45.0
    price_of_sweet = 0.42
    cost_of_children = characteristics.sweets_given * price_of_sweet
    remaining_money = money - cost_of_children
    time_it_took_assuming_parallel_eating = (
        time_to_eat_sweet * characteristics.number_of_sweet_per_child
    )
    return (
        f"{cost_of_children}¤ of sweets in "
        f"{time_it_took_assuming_parallel_eating}, you still have {remaining_money}"
    )

Configuration file:

[design]
max-locals = 11

Additional details:

Having too many locals may indicate that you're doing too much in a function and that classes regrouping some attributes could be created. Maybe operations could be separated in multiple functions. Are all your variables really closely related ?

Created by the design checker.

  too-many-nested-blocks / R1702

Message emitted:

Too many nested blocks (%s/%s)

Description:

Used when a function or a method has too many nested blocks. This makes the code less understandable and maintainable.

Problematic code:

def correct_fruits(fruits):
    if len(fruits) > 1:  # [too-many-nested-blocks]
        if "apple" in fruits:
            if "orange" in fruits:
                count = fruits["orange"]
                if count % 2:
                    if "kiwi" in fruits:
                        if count == 2:
                            return True
    return False

Correct code:

def correct_fruits(fruits):
    if len(fruits) > 1 and "apple" in fruits and "orange" in fruits:
        count = fruits["orange"]
        if count % 2 and "kiwi" in fruits and count == 2:
            return True
    return False

Created by the refactoring checker.

  too-many-public-methods / R0904

Message emitted:

Too many public methods (%s/%s)

Description:

Used when class has too many public methods, try to reduce this to get a simpler (and so easier to use) class.

Problematic code:

class SpaceInvaders:  # [too-many-public-methods]
    def __init__(self):
        pass
    def fire_laser_beam(self):
        pass
    def deploy_shield(self):
        pass
    def launch_missile(self):
        pass
    def activate_super_laser(self):
        pass
    def summon_mothership(self):
        pass
    def destroy_planet(self):
        pass
    def teleport(self):
        pass
    def invoke_aliens(self):
        pass
    def invade_earth(self):
        pass
    def takeover_galaxy(self):
        pass

Correct code:

class LaserBeam:
    def __init__(self):
        pass
    def fire(self):
        pass
    def activate_super(self):
        pass
    def destroy_planet(self):
        pass
class Shield:
    def deploy(self):
        pass
class Missile:
    def launch(self):
        pass
class SpaceInvaders:
    def __init__(self):
        self.laser = LaserBeam()
        self.shield = Shield()
        self.missile = Missile()
    def summon_mothership(self):
        pass
    def destroy_planet(self):
        pass
    def teleport(self):
        pass
    def invoke_aliens(self):
        pass
    def invade_earth(self):
        pass
    def takeover_galaxy(self):
        pass

Configuration file:

[main]
max-public-methods=7

Additional details:

Having too many public methods is an indication that you might not be respecting the Single-responsibility principle (S of SOLID).

The class should have only one reason to change, but in the example the spaceship has at least 4 persons that could ask for change to it (laser manager, shield manager, missile manager, teleportation officer...).

Related links:

•   Single-responsibility principle

    Created by the design checker.

  too-many-return-statements / R0911

Message emitted:

Too many return statements (%s/%s)

Description:

Used when a function or method has too many return statement, making it hard to follow.

Problematic code:

def to_string(x):  # [too-many-return-statements]
    # max of 6 by default, can be configured
    if x == 1:
        return 'This is one.'
    if x == 2:
        return 'This is two.'
    if x == 3:
        return 'This is three.'
    if x == 4:
        return 'This is four.'
    if x == 5:
        return 'This is five.'
    if x == 6:
        return 'This is six.'
    if x == 7:
        return 'This is seven.'

Correct code:

NUMBERS_TO_STRINGS = {
    1: 'one',
    2: 'two',
    3: 'three',
    4: 'four',
    5: 'five',
    6: 'six',
    7: 'seven'
}
def to_string(x):
    return f'This is {NUMBERS_TO_STRINGS.get(x)}.'

Created by the design checker.

  too-many-statements / R0915

Message emitted:

Too many statements (%s/%s)

Description:

Used when a function or method has too many statements. You should then split it in smaller functions / methods.

Problematic code:

import random
def distribute_candies(  # [too-many-statements]
    children: list[Child], candies_per_child: int
):
    # This function is a masterpiece of code that embodies the epitome of efficiency
    # it's also an essential part of a high-priority project with extremely tight deadlines
    # and there is absolutely no time to refactor it to make it more concise.
    # The lead developer on the project, who has decades of experience,
    # has personally reviewed this implementation and deemed it good enough as it is.
    # The person writing this code has a demanding job and multiple responsibilities,
    # and simply does not have the luxury of spending time making this code more readable.
    total_candies = len(children) * candies_per_child
    eaten_candies = 0
    # Counting candies given to each child
    for child in children:
        # If a child eat more than 1 candies they're going to eat all
        # the candies for sure
        eaten_for_child = random.choices([0, 1, candies_per_child])
        print(
            f"Child {child} gets {candies_per_child} candies and eat {eaten_for_child}"
        )
        remaining_candies_for_children = child.eat_candies(eaten_for_child)
        if remaining_candies_for_children == 0:
            print(f"All the candies have been devoured by {child.name}!")
        else:
            print(
                f"{child.name} still have {remaining_candies_for_children} candies left."
            )
        eaten_candies += eaten_for_child
    return eaten_candies, total_candies

Correct code:

import random
def distribute_candies(children: list[Child], candies_per_child: int):
    total_candies = len(children) * candies_per_child
    eaten_candies = 0
    for child in children:
        eaten_candies += _distribute_candies_to_child(candies_per_child, child)
    return eaten_candies, total_candies
def _distribute_candies_to_child(candies_per_child: int, child: Child):
    # If a child eat more than 1 candies they're going to eat all
    # the candies for sure
    eaten_for_child = random.choices([0, 1, candies_per_child])
    print(f"Child {child} gets {candies_per_child} candies and eat {eaten_for_child}")
    remaining_candies_for_children = child.eat_candies(eaten_for_child)
    if remaining_candies_for_children == 0:
        print(f"All the candies have been devoured by {child.name}!")
    else:
        print(f"{child.name} still have {remaining_candies_for_children} candies left.")
    return eaten_for_child

Configuration file:

[DESIGN]
max-statements=7

Created by the design checker.

  trailing-comma-tuple / R1707

Message emitted:

Disallow trailing comma tuple

Description:

In Python, a tuple is actually created by the comma symbol, not by the parentheses. Unfortunately, one can actually create a tuple by misplacing a trailing comma, which can lead to potential weird bugs in your code. You should always use parentheses explicitly for creating a tuple.

Problematic code:

COMPASS = "north", "south", "east", "west",  # [trailing-comma-tuple]

Correct code:

COMPASS = ("north", "south", "east", "west")

Created by the refactoring checker.

  unnecessary-comprehension / R1721

Message emitted:

Unnecessary use of a comprehension, use %s instead.

Description:

Instead of using an identity comprehension, consider using the list, dict or set constructor. It is faster and simpler.

Problematic code:

NUMBERS = [1, 1, 2, 2, 3, 3]
UNIQUE_NUMBERS = {number for number in NUMBERS}  # [unnecessary-comprehension]

Correct code:

NUMBERS = [1, 1, 2, 2, 3, 3]
UNIQUE_NUMBERS = set(NUMBERS)

Created by the refactoring checker.

  unnecessary-dict-index-lookup / R1733

Message emitted:

Unnecessary dictionary index lookup, use '%s' instead

Description:

Emitted when iterating over the dictionary items (key-item pairs) and accessing the value by index lookup. The value can be accessed directly instead.

Problematic code:

FRUITS = {"apple": 1, "orange": 10, "berry": 22}
for fruit_name, fruit_count in FRUITS.items():
    print(FRUITS[fruit_name])  # [unnecessary-dict-index-lookup]

Correct code:

FRUITS = {"apple": 1, "orange": 10, "berry": 22}
for fruit_name, fruit_count in FRUITS.items():
    print(fruit_count)

Created by the refactoring checker.

  unnecessary-list-index-lookup / R1736

Message emitted:

Unnecessary list index lookup, use '%s' instead

Description:

Emitted when iterating over an enumeration and accessing the value by index lookup. The value can be accessed directly instead.

Problematic code:

letters = ['a', 'b', 'c']
for index, letter in enumerate(letters):
    print(letters[index])  # [unnecessary-list-index-lookup]

Correct code:

letters = ['a', 'b', 'c']
for index, letter in enumerate(letters):
    print(letter)

Created by the refactoring checker.

  use-a-generator / R1729

Message emitted:

Use a generator instead '%s(%s)'

Description:

Comprehension inside of 'any', 'all', 'max', 'min' or 'sum' is unnecessary. A generator would be sufficient and faster.

Problematic code:

from random import randint
all([randint(-5, 5) > 0 for _ in range(10)])  # [use-a-generator]
any([randint(-5, 5) > 0 for _ in range(10)])  # [use-a-generator]

Correct code:

from random import randint
all(randint(-5, 5) > 0 for _ in range(10))
any(randint(-5, 5) > 0 for _ in range(10))

Additional details:

By using a generator you can cut the execution tree and exit directly at the first element that is False for all or True for any instead of calculating all the elements. Except in the worst possible case where you still need to evaluate everything (all values are True for all or all values are false for any) performance will be better.

Related links:

•   PEP 289 – Generator Expressions

•   Benchmark and discussion during initial implementation

    Created by the refactoring checker.

  use-dict-literal / R1735

Message emitted:

Consider using '%s' instead of a call to 'dict'.

Description:

Emitted when using dict() to create a dictionary instead of a literal '{ ... }'. The literal is faster as it avoids an additional function call.

Problematic code:

empty_dict = dict()  # [use-dict-literal]
new_dict = dict(foo="bar")  # [use-dict-literal]
new_dict = dict(**another_dict)  # [use-dict-literal]

Correct code:

empty_dict = {}
# create using a literal dict
new_dict = {"foo": "bar"}
# shallow copy a dict
new_dict = {**another_dict}

Additional details:

https://gist.github.com/hofrob/ad143aaa84c096f42489c2520a3875f9

This example script shows an 18% increase in performance when using a literal over the constructor in python version 3.10.6.

Created by the refactoring checker.

  use-list-literal / R1734

Message emitted:

Consider using [] instead of list()

Description:

Emitted when using list() to create an empty list instead of the literal []. The literal is faster as it avoids an additional function call.

Problematic code:

empty_list = list()  # [use-list-literal]

Correct code:

empty_list = []

Created by the refactoring checker.

  use-set-for-membership / R6201

Message emitted:

Consider using set for membership test

Description:

Membership tests are more efficient when performed on a lookup optimized datatype like ``sets``.

Problematic code:

def fruit_is_dangerous_for_cat(fruit: str) -> bool:
    """This list is only a silly example, don't make decision regarding your cat diet based on it."""
    return fruit in ["cherry", "grapes"]  # [use-set-for-membership]

Correct code:

def fruit_is_dangerous_for_cat(fruit: str) -> bool:
    """This list is only a silly example, don't make decision regarding your cat diet based on it."""
    return fruit in {"cherry", "grapes"}

Configuration file:

[MAIN]
load-plugins=pylint.extensions.set_membership

NOTE:

This message is emitted by the optional 'set_membership'
    checker which requires the pylint.extensions.set_membership plugin to be loaded.

    Created by the set_membership checker.

  useless-object-inheritance / R0205

Message emitted:

Class %r inherits from object, can be safely removed from bases in python3

Description:

Used when a class inherit from object, which under python3 is implicit, hence can be safely removed from bases.

Problematic code:

class Banana(object):  # [useless-object-inheritance]
    ...

Correct code:

class Banana:
    ...

Created by the classes checker.

  useless-return / R1711

Message emitted:

Useless return at end of function or method

Description:

Emitted when a single "return" or "return None" statement is found at the end of function or method definition. This statement can safely be removed because Python will implicitly return None

Problematic code:

import sys
def print_python_version():  # [useless-return]
    print(sys.version)
    return None

Correct code:

import sys
def print_python_version():
    print(sys.version)

Created by the refactoring checker.

All renamed messages in the refactor category:

  old-no-self-use / R0201

'old-no-self-use' has been renamed. The new message can be found at:

  old-simplifiable-if-statement / R0102

'old-simplifiable-if-statement' has been renamed. The new message can be found at:

  old-too-many-nested-blocks / R0101

'old-too-many-nested-blocks' has been renamed. The new message can be found at:

  Information

All messages in the information category:

  bad-inline-option / I0010

Message emitted:

Unable to consider inline option %r

Description:

Used when an inline option is either badly formatted or can't be used inside modules.

Problematic code:

# 2:[bad-inline-option]
# pylint: disable line-too-long

Correct code:

# pylint: disable=line-too-long

Created by the main checker.

  c-extension-no-member / I1101

Message emitted:

%s %r has no %r member%s, but source is unavailable. Consider adding this module to extension-pkg-allow-list if you want to perform analysis based on run-time introspection of living objects.

Description:

Used when a variable is accessed for non-existent member of C extension. Due to unavailability of source static analysis is impossible, but it may be performed by introspecting living objects in run-time.

Correct code:

# This is a placeholder for correct code for this message.

Additional details:

You can help us make the doc better by contributing !

Created by the typecheck checker.

  deprecated-pragma / I0022

Message emitted:

Pragma "%s" is deprecated, use "%s" instead

Description:

Some inline pylint options have been renamed or reworked, only the most recent form should be used. NOTE:skip-all is only available with pylint >= 0.26

Problematic code:

# pylint: disable-msg=eval-used # [deprecated-pragma]

Correct code:

# pylint: disable = eval-used

Created by the main checker.

  file-ignored / I0013

Message emitted:

Ignoring entire file

Description:

Used to inform that the file will not be checked

Problematic code:

# pylint: skip-file
# -1: [file-ignored]

Correct code:

Additional details:

There's no checks at all for a file if it starts by # pylint: skip-file.

Created by the main checker.

  locally-disabled / I0011

Message emitted:

Locally disabling %s (%s)

Description:

Used when an inline option disables a message or a messages category.

Problematic code:

def wizard_spells(spell_book):
    # pylint: disable=maybe-no-member # [locally-disabled]
    for spell in spell_book:
        print(f"Abracadabra! {spell}.")
spell_list = ["Levitation", "Invisibility", "Fireball", "Teleportation"]
wizard_spells(spell_list)

Correct code:

def wizard_spells(spell_book):
    for spell in spell_book:
        print(f"Abracadabra! {spell}.")
spell_list = ["Levitation", "Invisibility", "Fireball", "Teleportation"]
wizard_spells(spell_list)

Created by the main checker.

  raw-checker-failed / I0001

Message emitted:

Unable to run raw checkers on built-in module %s

Description:

Used to inform that a built-in module has not been checked using the raw checkers.

Correct code:

# This is a placeholder for correct code for this message.

Additional details:

You can help us make the doc better by contributing !

Created by the main checker.

  suppressed-message / I0020

Message emitted:

Suppressed %s (from line %d)

Description:

A message was triggered on a line, but suppressed explicitly by a disable= comment in the file. This message is not generated for messages that are ignored due to configuration settings.

Problematic code:

### This is a contrived example, to show how suppressed-message works.
### First we enable all messages
# pylint: enable=all
### Here we disable two messages so we get two warnings
# pylint: disable=locally-disabled, useless-suppression # [suppressed-message, suppressed-message]
### Here we disable a message, so we get a warning for suppressed-message again.
"A"  # pylint: disable=pointless-statement # [suppressed-message, suppressed-message]

Correct code:

"""Instead of a single string somewhere in the file, write a module docstring!"""

Additional details:

suppressed-message is simply a way to see messages that would be raised without the disable in your codebase. It should not be activated most of the time. See also useless-suppression if you want to see the message that are disabled for no reasons.

Created by the main checker.

  use-symbolic-message-instead / I0023

Message emitted:

%s

Description:

Used when a message is enabled or disabled by id.

Problematic code:

fruit_name = "plum"
# pylint: disable-next=W0621
def eat(fruit_name: str):  # [use-symbolic-message-instead]
    ...

Correct code:

fruit_name = "plum"
# pylint: disable-next=redefined-outer-name
def eat(fruit_name: str):
    ...

Created by the miscellaneous checker.

  useless-suppression / I0021

Message emitted:

Useless suppression of %s

Description:

Reported when a message is explicitly disabled for a line or a block of code, but never triggered.

Problematic code:

fruit_counter = 0
# pylint: disable-next=redefined-outer-name
def eat(fruit_name: str):  # [useless-suppression]
    ...

Correct code:

fruit_counter = 0
def eat(fruit_name: str):
    ...

Created by the main checker.

All renamed messages in the information category:

  deprecated-disable-all / I0014

'deprecated-disable-all' has been renamed. The new message can be found at:

  Messages control

In order to control messages, pylint accepts the following values:

•   a symbolic message: no-member, undefined-variable etc.

•   a numerical ID: E1101, E1102 etc.

•   The name of the group of checks. You can grab those with pylint --list-groups. For example, you can disable / enable all the checks related to type checking, with typecheck or all the checks related to variables with variables

•   Corresponding category of the checks

•   C convention related checks

•   R refactoring related checks

•   W various warnings

•   E errors, for probable bugs in the code

•   F fatal, if an error occurred which prevented pylint from doing further processing.

•   All the checks with all

  Block disables

This describes how the pragma controls operate at a code level.

The pragma controls can disable / enable:

•   All the violations on a single line

    a, b = ... # pylint: disable=unbalanced-tuple-unpacking

•   All the violations on the following line

    # pylint: disable-next=unbalanced-tuple-unpacking
    a, b = ...

•   All the violations in a single scope

    def test():
        # Disable all the no-member violations in this function
        # pylint: disable=no-member
        ...

•   All the violations in a block. For instance, each separate branch of an if statement is considered a separate block, as in the following example:

    def meth5(self):
        # pylint: disable=no-member
        # no error
        print(self.bla)
        if self.blop:
            # pylint: enable=no-member
            # enable all no-members for this block
            print(self.blip)
        else:
            # This is affected by the scope disable
            print(self.blip)
        # pylint: enable=no-member
        print(self.blip)
        if self.blop:
            # pylint: disable=no-member
            # disable all no-members for this block
            print(self.blip)
        else:
            # This emits a violation
            print(self.blip)

•   If the violation occurs on a block starting line, then it applies only to that line

    if self.blop: # pylint: disable=no-member; applies only to this line
        # Here we get an error
        print(self.blip)
    else:
        # error
        print(self.blip)

    Here's an example with all these rules in a single place:

    """pylint option block-disable"""
    __revision__ = None
    class Foo(object):
        """block-disable test"""
        def __init__(self):
            pass
        def meth1(self, arg):
            """this issues a message"""
            print(self)
        def meth2(self, arg):
            """and this one not"""
            # pylint: disable=unused-argument
            print(self\
                  + "foo")
        def meth3(self):
            """test one line disabling"""
            # no error
            print(self.bla) # pylint: disable=no-member
            # error
            print(self.blop)
        def meth4(self):
            """test re-enabling"""
            # pylint: disable=no-member
            # no error
            print(self.bla)
            print(self.blop)
            # pylint: enable=no-member
            # error
            print(self.blip)
        def meth5(self):
            """test IF sub-block re-enabling"""
            # pylint: disable=no-member
            # no error
            print(self.bla)
            if self.blop:
                # pylint: enable=no-member
                # error
                print(self.blip)
            else:
                # no error
                print(self.blip)
            # no error
            print(self.blip)
        def meth6(self):
            """test TRY/EXCEPT sub-block re-enabling"""
            # pylint: disable=no-member
            # no error
            print(self.bla)
            try:
                # pylint: enable=no-member
                # error
                print(self.blip)
            except UndefinedName: # pylint: disable=undefined-variable
                # no error
                print(self.blip)
            # no error
            print(self.blip)
        def meth7(self):
            """test one line block opening disabling"""
            if self.blop: # pylint: disable=no-member
                # error
                print(self.blip)
            else:
                # error
                print(self.blip)
            # error
            print(self.blip)
        def meth8(self):
            """test late disabling"""
            # error
            print(self.blip)
            # pylint: disable=no-member
            # no error
            print(self.bla)
            print(self.blop)
        def meth9(self):
            """test next line disabling"""
            # no error
            # pylint: disable-next=no-member
            print(self.bla)
            # error
            print(self.blop)

  Detecting useless disables

As pylint gets better and false positives are removed, disables that became useless can accumulate and clutter the code. In order to clean them you can enable the useless-suppression warning.

  Messages categories

Pylint can emit various messages. These are categorized according to categories corresponding to bit-encoded exit codes:

•   Fatal (1)

•   Error (2)

•   Warning (4)

•   Convention (8)

•   Refactor (16)

•   Information (NA)

    An overview of these messages can be found in Messages overview

  Disabling messages

pylint has an advanced message control for its checks, offering the ability to enable / disable a message either from the command line or from the configuration file, as well as from the code itself.

For more detail see Messages control

  Configuration

Pylint is highly configurable. There are a lot of options to follow the needs of various projects and a lot of checks to activate if they suit your style.

You can generate a sample configuration file with --generate-toml-config or --generate-rcfile. Every option present on the command line before this will be included in the file.

For example:

pylint --disable=bare-except,invalid-name --class-rgx='[A-Z][a-z]+' --generate-toml-config

In practice, it is often better to create a minimal configuration file which only contains configuration overrides. For all other options, Pylint will use its default values.

NOTE: The internals that create the configuration files fall back to the default values if no other value was given. This means that some values depend on the interpreter that was used to generate the file. Most notably py-version which defaults to the current interpreter.

  Standard Checkers

  Main Checker

  --analyse-fallback-blocks

Analyse import fallback blocks. This can be used to support both Python 2 and 3 compatible code, which means that the block might have code that exists only in one or another interpreter, leading to false positives when analysed.

Default: False

  --clear-cache-post-run

Clear in-memory caches upon conclusion of linting. Useful if running pylint in a server-like mode.

Default: False

  --confidence

Only show warnings with the listed confidence levels. Leave empty to show all. Valid levels: HIGH, CONTROL_FLOW, INFERENCE, INFERENCE_FAILURE, UNDEFINED.

Default: ['HIGH', 'CONTROL_FLOW', 'INFERENCE', 'INFERENCE_FAILURE', 'UNDEFINED']

  --disable

Disable the message, report, category or checker with the given id(s). You can either give multiple identifiers separated by comma (,) or put this option multiple times (only on the command line, not in the configuration file where it should appear only once). You can also use "--disable=all" to disable everything first and then re-enable specific checks. For example, if you want to run only the similarities checker, you can use "--disable=all --enable=similarities". If you want to run only the classes checker, but have no Warning level messages displayed, use "--disable=all --enable=classes --disable=W".

Default: ()

  --enable

Enable the message, report, category or checker with the given id(s). You can either give multiple identifier separated by comma (,) or put this option multiple time (only on the command line, not in the configuration file where it should appear only once). See also the "--disable" option for examples.

Default: ()

  --evaluation

Python expression which should return a score less than or equal to 10. You have access to the variables 'fatal', 'error', 'warning', 'refactor', 'convention', and 'info' which contain the number of messages in each category, as well as 'statement' which is the total number of statements analyzed. This score is used by the global evaluation report (RP0004).

Default: max(0, 0 if fatal else 10.0 - ((float(5 * error + warning + refactor + convention) / statement) * 10))

  --exit-zero

Always return a 0 (non-error) status code, even if lint errors are found. This is primarily useful in continuous integration scripts.

Default: False

  --extension-pkg-allow-list

A comma-separated list of package or module names from where C extensions may be loaded. Extensions are loading into the active Python interpreter and may run arbitrary code.

Default: []

  --extension-pkg-whitelist

A comma-separated list of package or module names from where C extensions may be loaded. Extensions are loading into the active Python interpreter and may run arbitrary code. (This is an alternative name to extension-pkg-allow-list for backward compatibility.)

Default: []

  --fail-on

Return non-zero exit code if any of these messages/categories are detected, even if score is above --fail-under value. Syntax same as enable. Messages specified are enabled, while categories only check already-enabled messages.

Default: ""

  --fail-under

Specify a score threshold under which the program will exit with error.

Default: 10

  --from-stdin

Interpret the stdin as a python script, whose filename needs to be passed as the module_or_package argument.

Default: False

  --ignore

Files or directories to be skipped. They should be base names, not paths.

Default: ('CVS',)

  --ignore-paths

Add files or directories matching the regular expressions patterns to the ignore-list. The regex matches against paths and can be in Posix or Windows format. Because '\' represents the directory delimiter on Windows systems, it can't be used as an escape character.

Default: []

  --ignore-patterns

Files or directories matching the regular expression patterns are skipped. The regex matches against base names, not paths. The default value ignores Emacs file locks

Default: (re.compile('^\\.#'),)

  --ignored-modules

List of module names for which member attributes should not be checked (useful for modules/projects where namespaces are manipulated during runtime and thus existing member attributes cannot be deduced by static analysis). It supports qualified module names, as well as Unix pattern matching.

Default: ()

  --jobs

Use multiple processes to speed up Pylint. Specifying 0 will auto-detect the number of processors available to use, and will cap the count on Windows to avoid hangs.

Default: 1

  --limit-inference-results

Control the amount of potential inferred values when inferring a single object. This can help the performance when dealing with large functions or complex, nested conditions.

Default: 100

  --load-plugins

List of plugins (as comma separated values of python module names) to load, usually to register additional checkers.

Default: ()

  --msg-template

Template used to display messages. This is a python new-style format string used to format the message information. See doc for all details.

Default: ""

  --output-format

Set the output format. Available formats are text, parseable, colorized, json and msvs (visual studio). You can also give a reporter class, e.g. mypackage.mymodule.MyReporterClass.

Default: text

  --persistent

Pickle collected data for later comparisons.

Default: True

  --py-version

Minimum Python version to use for version dependent checks. Will default to the version used to run pylint.

Default: (3, 10)

  --recursive

Discover python modules and packages in the file system subtree.

Default: False

  --reports

Tells whether to display a full report or only the messages.

Default: False

  --score

Activate the evaluation score.

Default: True

  --source-roots

Add paths to the list of the source roots. Supports globbing patterns. The source root is an absolute path or a path relative to the current working directory used to determine a package namespace for modules located under the source root.

Default: ()

  --suggestion-mode

When enabled, pylint would attempt to guess common misconfiguration and emit user-friendly hints instead of false-positive error messages.

Default: True

  --unsafe-load-any-extension

Allow loading of arbitrary C extensions. Extensions are imported into the active Python interpreter and may run arbitrary code.

Default: False

Note: Only tool.pylint is required, the section title is not. These are the default values.

[tool.pylint.main]
analyse-fallback-blocks = false
clear-cache-post-run = false
confidence = ["HIGH", "CONTROL_FLOW", "INFERENCE", "INFERENCE_FAILURE", "UNDEFINED"]
disable = ["consider-using-augmented-assign"]
enable = []
evaluation = "max(0, 0 if fatal else 10.0 - ((float(5 * error + warning + refactor + convention) / statement) * 10))"
exit-zero = false
extension-pkg-allow-list = []
extension-pkg-whitelist = []
fail-on = []
fail-under = 10
from-stdin = false
ignore = ["CVS"]
ignore-paths = []
ignore-patterns = ["^\\.#"]
ignored-modules = []
jobs = 1
limit-inference-results = 100
load-plugins = []
msg-template = ""
# output-format =
persistent = true
py-version = [3, 10]
recursive = false
reports = false
score = true
source-roots = []
suggestion-mode = true
unsafe-load-any-extension = false

  Basic Checker

  --argument-naming-style

Naming style matching correct argument names.

Default: snake_case

  --argument-rgx

Regular expression matching correct argument names. Overrides argument-naming-style. If left empty, argument names will be checked with the set naming style.

Default: None

  --attr-naming-style

Naming style matching correct attribute names.

Default: snake_case

  --attr-rgx

Regular expression matching correct attribute names. Overrides attr-naming-style. If left empty, attribute names will be checked with the set naming style.

Default: None

  --bad-names

Bad variable names which should always be refused, separated by a comma.

Default: ('foo', 'bar', 'baz', 'toto', 'tutu', 'tata')

  --bad-names-rgxs

Bad variable names regexes, separated by a comma. If names match any regex, they will always be refused

Default: ""

  --class-attribute-naming-style

Naming style matching correct class attribute names.

Default: any

  --class-attribute-rgx

Regular expression matching correct class attribute names. Overrides class-attribute-naming-style. If left empty, class attribute names will be checked with the set naming style.

Default: None

  --class-const-naming-style

Naming style matching correct class constant names.

Default: UPPER_CASE

  --class-const-rgx

Regular expression matching correct class constant names. Overrides class-const-naming-style. If left empty, class constant names will be checked with the set naming style.

Default: None

  --class-naming-style

Naming style matching correct class names.

Default: PascalCase

  --class-rgx

Regular expression matching correct class names. Overrides class-naming-style. If left empty, class names will be checked with the set naming style.

Default: None

  --const-naming-style

Naming style matching correct constant names.

Default: UPPER_CASE

  --const-rgx

Regular expression matching correct constant names. Overrides const-naming-style. If left empty, constant names will be checked with the set naming style.

Default: None

  --docstring-min-length

Minimum line length for functions/classes that require docstrings, shorter ones are exempt.

Default: -1

  --function-naming-style

Naming style matching correct function names.

Default: snake_case

  --function-rgx

Regular expression matching correct function names. Overrides function-naming-style. If left empty, function names will be checked with the set naming style.

Default: None

  --good-names

Good variable names which should always be accepted, separated by a comma.

Default: ('i', 'j', 'k', 'ex', 'Run', '_')

  --good-names-rgxs

Good variable names regexes, separated by a comma. If names match any regex, they will always be accepted

Default: ""

  --include-naming-hint

Include a hint for the correct naming format with invalid-name.

Default: False

  --inlinevar-naming-style

Naming style matching correct inline iteration names.

Default: any

  --inlinevar-rgx

Regular expression matching correct inline iteration names. Overrides inlinevar-naming-style. If left empty, inline iteration names will be checked with the set naming style.

Default: None

  --method-naming-style

Naming style matching correct method names.

Default: snake_case

  --method-rgx

Regular expression matching correct method names. Overrides method-naming-style. If left empty, method names will be checked with the set naming style.

Default: None

  --module-naming-style

Naming style matching correct module names.

Default: snake_case

  --module-rgx

Regular expression matching correct module names. Overrides module-naming-style. If left empty, module names will be checked with the set naming style.

Default: None

  --name-group

Colon-delimited sets of names that determine each other's naming style when the name regexes allow several styles.

Default: ()

  --no-docstring-rgx

Regular expression which should only match function or class names that do not require a docstring.

Default: re.compile('^_')

  --property-classes

List of decorators that produce properties, such as abc.abstractproperty. Add to this list to register other decorators that produce valid properties. These decorators are taken in consideration only for invalid-name.

Default: ('abc.abstractproperty',)

  --typealias-rgx

Regular expression matching correct type alias names. If left empty, type alias names will be checked with the set naming style.

Default: None

  --typevar-rgx

Regular expression matching correct type variable names. If left empty, type variable names will be checked with the set naming style.

Default: None

  --variable-naming-style

Naming style matching correct variable names.

Default: snake_case

  --variable-rgx

Regular expression matching correct variable names. Overrides variable-naming-style. If left empty, variable names will be checked with the set naming style.

Default: None

Note: Only tool.pylint is required, the section title is not. These are the default values.

[tool.pylint.basic]
argument-naming-style = "snake_case"
# argument-rgx =
attr-naming-style = "snake_case"
# attr-rgx =
bad-names = ["foo", "bar", "baz", "toto", "tutu", "tata"]
bad-names-rgxs = []
class-attribute-naming-style = "any"
# class-attribute-rgx =
class-const-naming-style = "UPPER_CASE"
# class-const-rgx =
class-naming-style = "PascalCase"
# class-rgx =
const-naming-style = "UPPER_CASE"
# const-rgx =
docstring-min-length = -1
function-naming-style = "snake_case"
# function-rgx =
good-names = ["i", "j", "k", "ex", "Run", "_"]
good-names-rgxs = []
include-naming-hint = false
inlinevar-naming-style = "any"
# inlinevar-rgx =
method-naming-style = "snake_case"
# method-rgx =
module-naming-style = "snake_case"
# module-rgx =
name-group = []
no-docstring-rgx = "^_"
property-classes = ["abc.abstractproperty"]
# typealias-rgx =
# typevar-rgx =
variable-naming-style = "snake_case"
# variable-rgx =

  Classes Checker

  --check-protected-access-in-special-methods

Warn about protected attribute access inside special methods

Default: False

  --defining-attr-methods

List of method names used to declare (i.e. assign) instance attributes.

Default: ('__init__', '__new__', 'setUp', 'asyncSetUp', '__post_init__')

  --exclude-protected

List of member names, which should be excluded from the protected access warning.

Default: ('_asdict', '_fields', '_replace', '_source', '_make', 'os._exit')

  --valid-classmethod-first-arg

List of valid names for the first argument in a class method.

Default: ('cls',)

  --valid-metaclass-classmethod-first-arg

List of valid names for the first argument in a metaclass class method.

Default: ('mcs',)

Note: Only tool.pylint is required, the section title is not. These are the default values.

[tool.pylint.classes]
check-protected-access-in-special-methods = false
defining-attr-methods = ["__init__", "__new__", "setUp", "asyncSetUp", "__post_init__"]
exclude-protected = ["_asdict", "_fields", "_replace", "_source", "_make", "os._exit"]
valid-classmethod-first-arg = ["cls"]
valid-metaclass-classmethod-first-arg = ["mcs"]

  Design Checker

  --exclude-too-few-public-methods

List of regular expressions of class ancestor names to ignore when counting public methods (see R0903)

Default: []

  --ignored-parents

List of qualified class names to ignore when counting class parents (see R0901)

Default: ()

  --max-args

Maximum number of arguments for function / method.

Default: 5

  --max-attributes

Maximum number of attributes for a class (see R0902).

Default: 7

  --max-bool-expr

Maximum number of boolean expressions in an if statement (see R0916).

Default: 5

  --max-branches

Maximum number of branch for function / method body.

Default: 12

  --max-complexity

McCabe complexity cyclomatic threshold

Default: 10

  --max-locals

Maximum number of locals for function / method body.

Default: 15

  --max-parents

Maximum number of parents for a class (see R0901).

Default: 7

  --max-public-methods

Maximum number of public methods for a class (see R0904).

Default: 20

  --max-returns

Maximum number of return / yield for function / method body.

Default: 6

  --max-statements

Maximum number of statements in function / method body.

Default: 50

  --min-public-methods

Minimum number of public methods for a class (see R0903).

Default: 2

Note: Only tool.pylint is required, the section title is not. These are the default values.

[tool.pylint.design]
exclude-too-few-public-methods = []
ignored-parents = []
max-args = 5
max-attributes = 7
max-bool-expr = 5
max-branches = 12
max-complexity = 10
max-locals = 15
max-parents = 7
max-public-methods = 20
max-returns = 6
max-statements = 50
min-public-methods = 2

  Exceptions Checker

  --overgeneral-exceptions

Exceptions that will emit a warning when caught.

Default: ('builtins.BaseException', 'builtins.Exception')

Note: Only tool.pylint is required, the section title is not. These are the default values.

[tool.pylint.exceptions]
overgeneral-exceptions = ["builtins.BaseException", "builtins.Exception"]

  Format Checker

  --expected-line-ending-format

Expected format of line ending, e.g. empty (any line ending), LF or CRLF.

Default: ""

  --ignore-long-lines

Regexp for a line that is allowed to be longer than the limit.

Default: ^\s*(# )?<?https?://\S+>?$

  --indent-after-paren

Number of spaces of indent required inside a hanging or continued line.

Default: 4

  --indent-string

String used as indentation unit. This is usually " " (4 spaces) or "t" (1 tab).

Default: `` ``

  --max-line-length

Maximum number of characters on a single line.

Default: 100

  --max-module-lines

Maximum number of lines in a module.

Default: 1000

  --single-line-class-stmt

Allow the body of a class to be on the same line as the declaration if body contains single statement.

Default: False

  --single-line-if-stmt

Allow the body of an if to be on the same line as the test if there is no else.

Default: False

Note: Only tool.pylint is required, the section title is not. These are the default values.

[tool.pylint.format]
expected-line-ending-format = ""
ignore-long-lines = "^\\s*(# )?<?https?://\\S+>?$"
indent-after-paren = 4
indent-string = "    "
max-line-length = 100
max-module-lines = 1000
single-line-class-stmt = false
single-line-if-stmt = false

  Imports Checker

  --allow-any-import-level

List of modules that can be imported at any level, not just the top level one.

Default: ()

  --allow-reexport-from-package

Allow explicit reexports by alias from a package __init__.

Default: False

  --allow-wildcard-with-all

Allow wildcard imports from modules that define __all__.

Default: False

  --deprecated-modules

Deprecated modules which should not be used, separated by a comma.

Default: ()

  --ext-import-graph

Output a graph (.gv or any supported image format) of external dependencies to the given file (report RP0402 must not be disabled).

Default: ""

  --import-graph

Output a graph (.gv or any supported image format) of all (i.e. internal and external) dependencies to the given file (report RP0402 must not be disabled).

Default: ""

  --int-import-graph

Output a graph (.gv or any supported image format) of internal dependencies to the given file (report RP0402 must not be disabled).

Default: ""

  --known-standard-library

Force import order to recognize a module as part of the standard compatibility libraries.

Default: ()

  --known-third-party

Force import order to recognize a module as part of a third party library.

Default: ('enchant',)

  --preferred-modules

Couples of modules and preferred modules, separated by a comma.

Default: ()

Note: Only tool.pylint is required, the section title is not. These are the default values.

[tool.pylint.imports]
allow-any-import-level = []
allow-reexport-from-package = false
allow-wildcard-with-all = false
deprecated-modules = []
ext-import-graph = ""
import-graph = ""
int-import-graph = ""
known-standard-library = []
known-third-party = ["enchant"]
preferred-modules = []

  Logging Checker

  --logging-format-style

The type of string formatting that logging methods do. `old` means using % formatting, `new` is for `{}` formatting.

Default: old

  --logging-modules

Logging modules to check that the string format arguments are in logging function parameter format.

Default: ('logging',)

Note: Only tool.pylint is required, the section title is not. These are the default values.

[tool.pylint.logging]
logging-format-style = "old"
logging-modules = ["logging"]

  Method_args Checker

  --timeout-methods

List of qualified names (i.e., library.method) which require a timeout parameter e.g. 'requests.api.get,requests.api.post'

Default: ('requests.api.delete', 'requests.api.get', 'requests.api.head', 'requests.api.options', 'requests.api.patch', 'requests.api.post', 'requests.api.put', 'requests.api.request')

Note: Only tool.pylint is required, the section title is not. These are the default values.

[tool.pylint.method_args]
timeout-methods = ["requests.api.delete", "requests.api.get", "requests.api.head", "requests.api.options", "requests.api.patch", "requests.api.post", "requests.api.put", "requests.api.request"]

  Miscellaneous Checker

  --notes

List of note tags to take in consideration, separated by a comma.

Default: ('FIXME', 'XXX', 'TODO')

  --notes-rgx

Regular expression of note tags to take in consideration.

Default: ""

Note: Only tool.pylint is required, the section title is not. These are the default values.

[tool.pylint.miscellaneous]
notes = ["FIXME", "XXX", "TODO"]
notes-rgx = ""

  Refactoring Checker

  --max-nested-blocks

Maximum number of nested blocks for function / method body

Default: 5

  --never-returning-functions

Complete name of functions that never returns. When checking for inconsistent-return-statements if a never returning function is called then it will be considered as an explicit return statement and no message will be printed.

Default: ('sys.exit', 'argparse.parse_error')

Note: Only tool.pylint is required, the section title is not. These are the default values.

[tool.pylint.refactoring]
max-nested-blocks = 5
never-returning-functions = ["sys.exit", "argparse.parse_error"]

  Similarities Checker

  --ignore-comments

Comments are removed from the similarity computation

Default: True

  --ignore-docstrings

Docstrings are removed from the similarity computation

Default: True

  --ignore-imports

Imports are removed from the similarity computation

Default: True

  --ignore-signatures

Signatures are removed from the similarity computation

Default: True

  --min-similarity-lines

Minimum lines number of a similarity.

Default: 4

Note: Only tool.pylint is required, the section title is not. These are the default values.

[tool.pylint.similarities]
ignore-comments = true
ignore-docstrings = true
ignore-imports = true
ignore-signatures = true
min-similarity-lines = 4

  Spelling Checker

  --max-spelling-suggestions

Limits count of emitted suggestions for spelling mistakes.

Default: 4

  --spelling-dict

Spelling dictionary name. No available dictionaries : You need to install both the python package and the system dependency for enchant to work..

Default: ""

  --spelling-ignore-comment-directives

List of comma separated words that should be considered directives if they appear at the beginning of a comment and should not be checked.

Default: fmt: on,fmt: off,noqa:,noqa,nosec,isort:skip,mypy:

  --spelling-ignore-words

List of comma separated words that should not be checked.

Default: ""

  --spelling-private-dict-file

A path to a file that contains the private dictionary; one word per line.

Default: ""

  --spelling-store-unknown-words

Tells whether to store unknown words to the private dictionary (see the --spelling-private-dict-file option) instead of raising a message.

Default: n

Note: Only tool.pylint is required, the section title is not. These are the default values.

[tool.pylint.spelling]
max-spelling-suggestions = 4
spelling-dict = ""
spelling-ignore-comment-directives = "fmt: on,fmt: off,noqa:,noqa,nosec,isort:skip,mypy:"
spelling-ignore-words = ""
spelling-private-dict-file = ""
spelling-store-unknown-words = false

  String Checker

  --check-quote-consistency

This flag controls whether inconsistent-quotes generates a warning when the character used as a quote delimiter is used inconsistently within a module.

Default: False

  --check-str-concat-over-line-jumps

This flag controls whether the implicit-str-concat should generate a warning on implicit string concatenation in sequences defined over several lines.

Default: False

Note: Only tool.pylint is required, the section title is not. These are the default values.

[tool.pylint.string]
check-quote-consistency = false
check-str-concat-over-line-jumps = false

  Typecheck Checker

  --contextmanager-decorators

List of decorators that produce context managers, such as contextlib.contextmanager. Add to this list to register other decorators that produce valid context managers.

Default: ['contextlib.contextmanager']

  --generated-members

List of members which are set dynamically and missed by pylint inference system, and so shouldn't trigger E1101 when accessed. Python regular expressions are accepted.

Default: ()

  --ignore-mixin-members

Tells whether missing members accessed in mixin class should be ignored. A class is considered mixin if its name matches the mixin-class-rgx option.

Default: True

  --ignore-none

Tells whether to warn about missing members when the owner of the attribute is inferred to be None.

Default: True

  --ignore-on-opaque-inference

This flag controls whether pylint should warn about no-member and similar checks whenever an opaque object is returned when inferring. The inference can return multiple potential results while evaluating a Python object, but some branches might not be evaluated, which results in partial inference. In that case, it might be useful to still emit no-member and other checks for the rest of the inferred objects.

Default: True

  --ignored-checks-for-mixins

List of symbolic message names to ignore for Mixin members.

Default: ['no-member', 'not-async-context-manager', 'not-context-manager', 'attribute-defined-outside-init']

  --ignored-classes

List of class names for which member attributes should not be checked (useful for classes with dynamically set attributes). This supports the use of qualified names.

Default: ('optparse.Values', 'thread._local', '_thread._local', 'argparse.Namespace')

  --missing-member-hint

Show a hint with possible names when a member name was not found. The aspect of finding the hint is based on edit distance.

Default: True

  --missing-member-hint-distance

The minimum edit distance a name should have in order to be considered a similar match for a missing member name.

Default: 1

  --missing-member-max-choices

The total number of similar names that should be taken in consideration when showing a hint for a missing member.

Default: 1

  --mixin-class-rgx

Regex pattern to define which classes are considered mixins.

Default: .*[Mm]ixin

  --signature-mutators

List of decorators that change the signature of a decorated function.

Default: []

Note: Only tool.pylint is required, the section title is not. These are the default values.

[tool.pylint.typecheck]
contextmanager-decorators = ["contextlib.contextmanager"]
generated-members = []
ignore-mixin-members = true
ignore-none = true
ignore-on-opaque-inference = true
ignored-checks-for-mixins = ["no-member", "not-async-context-manager", "not-context-manager", "attribute-defined-outside-init"]
ignored-classes = ["optparse.Values", "thread._local", "_thread._local", "argparse.Namespace"]
missing-member-hint = true
missing-member-hint-distance = 1
missing-member-max-choices = 1
mixin-class-rgx = ".*[Mm]ixin"
signature-mutators = []

  Variables Checker

  --additional-builtins

List of additional names supposed to be defined in builtins. Remember that you should avoid defining new builtins when possible.

Default: ()

  --allow-global-unused-variables

Tells whether unused global variables should be treated as a violation.

Default: True

  --allowed-redefined-builtins

List of names allowed to shadow builtins

Default: ()

  --callbacks

List of strings which can identify a callback function by name. A callback name must start or end with one of those strings.

Default: ('cb_', '_cb')

  --dummy-variables-rgx

A regular expression matching the name of dummy variables (i.e. expected to not be used).

Default: _+$|(_[a-zA-Z0-9_]*[a-zA-Z0-9]+?$)|dummy|^ignored_|^unused_

  --ignored-argument-names

Argument names that match this expression will be ignored.

Default: re.compile('_.*|^ignored_|^unused_')

  --init-import

Tells whether we should check for unused import in __init__ files.

Default: False

  --redefining-builtins-modules

List of qualified module names which can have objects that can redefine builtins.

Default: ('six.moves', 'past.builtins', 'future.builtins', 'builtins', 'io')

Note: Only tool.pylint is required, the section title is not. These are the default values.

[tool.pylint.variables]
additional-builtins = []
allow-global-unused-variables = true
allowed-redefined-builtins = []
callbacks = ["cb_", "_cb"]
dummy-variables-rgx = "_+$|(_[a-zA-Z0-9_]*[a-zA-Z0-9]+?$)|dummy|^ignored_|^unused_"
ignored-argument-names = "_.*|^ignored_|^unused_"
init-import = false
redefining-builtins-modules = ["six.moves", "past.builtins", "future.builtins", "builtins", "io"]

  Extensions

  Broad_try_clause Checker

  --max-try-statements

Maximum number of statements allowed in a try clause

Default: 1

Note: Only tool.pylint is required, the section title is not. These are the default values.

[tool.pylint.broad_try_clause]
max-try-statements = 1

  Code_style Checker

  --max-line-length-suggestions

Max line length for which to sill emit suggestions. Used to prevent optional suggestions which would get split by a code formatter (e.g., black). Will default to the setting for ``max-line-length``.

Default: 0

Note: Only tool.pylint is required, the section title is not. These are the default values.

[tool.pylint.code_style]
max-line-length-suggestions = 0

  Deprecated_builtins Checker

  --bad-functions

List of builtins function names that should not be used, separated by a comma

Default: ['map', 'filter']

Note: Only tool.pylint is required, the section title is not. These are the default values.

[tool.pylint.deprecated_builtins]
bad-functions = ["map", "filter"]

  Dunder Checker

  --good-dunder-names

Good dunder names which should always be accepted.

Default: []

Note: Only tool.pylint is required, the section title is not. These are the default values.

[tool.pylint.dunder]
good-dunder-names = []

  Magic-value Checker

  --valid-magic-values

List of valid magic values that `magic-value-compare` will not detect. Supports integers, floats, negative numbers, for empty string enter ``''``, for backslash values just use one backslash e.g n.

Default: (0, -1, 1, '', '__main__')

Note: Only tool.pylint is required, the section title is not. These are the default values.

[tool.pylint.magic-value]
valid-magic-values = [0, -1, 1, "", "__main__"]

  Parameter_documentation Checker

  --accept-no-param-doc

Whether to accept totally missing parameter documentation in the docstring of a function that has parameters.

Default: True

  --accept-no-raise-doc

Whether to accept totally missing raises documentation in the docstring of a function that raises an exception.

Default: True

  --accept-no-return-doc

Whether to accept totally missing return documentation in the docstring of a function that returns a statement.

Default: True

  --accept-no-yields-doc

Whether to accept totally missing yields documentation in the docstring of a generator.

Default: True

  --default-docstring-type

If the docstring type cannot be guessed the specified docstring type will be used.

Default: default

Note: Only tool.pylint is required, the section title is not. These are the default values.

[tool.pylint.parameter_documentation]
accept-no-param-doc = true
accept-no-raise-doc = true
accept-no-return-doc = true
accept-no-yields-doc = true
default-docstring-type = "default"

  Typing Checker

  --runtime-typing

Set to ``no`` if the app / library does **NOT* need to support runtime introspection of type annotations. If you use type annotations exclusively for type checking of an application, you're probably fine. For libraries, evaluate if some users want to access the type hints at runtime first, e.g., through typing.get_type_hints. Applies to Python versions 3.7 - 3.9*

Default: True

Note: Only tool.pylint is required, the section title is not. These are the default values.

[tool.pylint.typing]
runtime-typing = true

  Checkers

  Pylint features

  Pylint checkers' options and switches

Pylint checkers can provide three set of features:

•   options that control their execution,

•   messages that they can raise,

•   reports that they can generate.

    Below is a list of all checkers and their features.

  Async checker

Verbatim name of the checker is async.

  Async checker Messages

not-async-context-manager (E1701)
    Async context manager '%s' doesn't implement __aenter__ and __aexit__. Used when an async context manager is used with an object that does not implement the async context management protocol. This message can't be emitted when using Python < 3.5.

yield-inside-async-function (E1700)
    Yield inside async function Used when an yield or yield from statement is found inside an async function. This message can't be emitted when using Python < 3.5.

  Bad-Chained-Comparison checker

Verbatim name of the checker is bad-chained-comparison.

  Bad-Chained-Comparison checker Messages

bad-chained-comparison (W3601)
    Suspicious %s-part chained comparison using semantically incompatible operators (%s) Used when there is a chained comparison where one expression is part of two comparisons that belong to different semantic groups ("<" does not mean the same thing as "is", chaining them in "0 < x is None" is probably a mistake).

  Basic checker

Verbatim name of the checker is basic.

See also basic checker's options' documentation

  Basic checker Messages

not-in-loop (E0103)
    %r not properly in loop Used when break or continue keywords are used outside a loop.

function-redefined (E0102)
    %s already defined line %s Used when a function / class / method is redefined.

continue-in-finally (E0116)
    'continue' not supported inside 'finally' clause Emitted when the continue keyword is found inside a finally clause, which is a SyntaxError.

abstract-class-instantiated (E0110)
    Abstract class %r with abstract methods instantiated Used when an abstract class with abc.ABCMeta as metaclass has abstract methods and is instantiated.

star-needs-assignment-target (E0114)
    Can use starred expression only in assignment target Emitted when a star expression is not used in an assignment target.

duplicate-argument-name (E0108)
    Duplicate argument name %s in function definition Duplicate argument names in function definitions are syntax errors.

return-in-init (E0101)
    Explicit return in __init__ Used when the special class method __init__ has an explicit return value.

too-many-star-expressions (E0112)
    More than one starred expression in assignment Emitted when there are more than one starred expressions (*x) in an assignment. This is a SyntaxError.

nonlocal-and-global (E0115)
    Name %r is nonlocal and global Emitted when a name is both nonlocal and global.

used-prior-global-declaration (E0118)
    Name %r is used prior to global declaration Emitted when a name is used prior a global declaration, which results in an error since Python 3.6. This message can't be emitted when using Python < 3.6.

return-outside-function (E0104)
    Return outside function Used when a "return" statement is found outside a function or method.

return-arg-in-generator (E0106)
    Return with argument inside generator Used when a "return" statement with an argument is found outside in a generator function or method (e.g. with some "yield" statements). This message can't be emitted when using Python >= 3.3.

invalid-star-assignment-target (E0113)
    Starred assignment target must be in a list or tuple Emitted when a star expression is used as a starred assignment target.

bad-reversed-sequence (E0111)
    The first reversed() argument is not a sequence Used when the first argument to reversed() builtin isn't a sequence (does not implement __reversed__, nor __getitem__ and __len__

nonexistent-operator (E0107)
    Use of the non-existent %s operator Used when you attempt to use the C-style pre-increment or pre-decrement operator -- and ++, which doesn't exist in Python.

yield-outside-function (E0105)
    Yield outside function Used when a "yield" statement is found outside a function or method.

init-is-generator (E0100)
    __init__ method is a generator Used when the special class method __init__ is turned into a generator by a yield in its body.

misplaced-format-function (E0119)
    format function is not called on str Emitted when format function is not called on str object. e.g doing print("value: {}").format(123) instead of print("value: {}".format(123)). This might not be what the user intended to do.

nonlocal-without-binding (E0117)
    nonlocal name %s found without binding Emitted when a nonlocal variable does not have an attached name somewhere in the parent scopes

lost-exception (W0150)
    %s statement in finally block may swallow exception Used when a break or a return statement is found inside the finally clause of a try...finally block: the exceptions raised in the try clause will be silently swallowed instead of being re-raised.

assert-on-tuple (W0199)
    Assert called on a populated tuple. Did you mean 'assert x,y'? A call of assert on a tuple will always evaluate to true if the tuple is not empty, and will always evaluate to false if it is.

assert-on-string-literal (W0129)
    Assert statement has a string literal as its first argument. The assert will %s fail. Used when an assert statement has a string literal as its first argument, which will cause the assert to always pass.

self-assigning-variable (W0127)
    Assigning the same variable %r to itself Emitted when we detect that a variable is assigned to itself

comparison-with-callable (W0143)
    Comparing against a callable, did you omit the parenthesis? This message is emitted when pylint detects that a comparison with a callable was made, which might suggest that some parenthesis were omitted, resulting in potential unwanted behaviour.

nan-comparison (W0177)
    Comparison %s should be %s Used when an expression is compared to NaN values like numpy.NaN and float('nan').

dangerous-default-value (W0102)
    Dangerous default value %s as argument Used when a mutable value as list or dictionary is detected in a default value for an argument.

duplicate-key (W0109)
    Duplicate key %r in dictionary Used when a dictionary expression binds the same key multiple times.

duplicate-value (W0130)
    Duplicate value %r in set This message is emitted when a set contains the same value two or more times.

useless-else-on-loop (W0120)
    Else clause on loop without a break statement, remove the else and de-indent all the code inside it Loops should only have an else clause if they can exit early with a break statement, otherwise the statements under else should be on the same scope as the loop itself.

pointless-exception-statement (W0133)
    Exception statement has no effect Used when an exception is created without being assigned, raised or returned for subsequent use elsewhere.

expression-not-assigned (W0106)
    Expression "%s" is assigned to nothing Used when an expression that is not a function call is assigned to nothing. Probably something else was intended.

confusing-with-statement (W0124)
    Following "as" with another context manager looks like a tuple. Emitted when a with statement component returns multiple values and uses name binding with as only for a part of those values, as in with ctx() as a, b. This can be misleading, since it's not clear if the context manager returns a tuple or if the node without a name binding is another context manager.

unnecessary-lambda (W0108)
    Lambda may not be necessary Used when the body of a lambda expression is a function call on the same argument list as the lambda itself; such lambda expressions are in all but a few cases replaceable with the function being called in the body of the lambda.

named-expr-without-context (W0131)
    Named expression used without context Emitted if named expression is used to do a regular assignment outside a context like if, for, while, or a comprehension.

redeclared-assigned-name (W0128)
    Redeclared variable %r in assignment Emitted when we detect that a variable was redeclared in the same assignment.

pointless-statement (W0104)
    Statement seems to have no effect Used when a statement doesn't have (or at least seems to) any effect.

pointless-string-statement (W0105)
    String statement has no effect Used when a string is used as a statement (which of course has no effect). This is a particular case of W0104 with its own message so you can easily disable it if you're using those strings as documentation, instead of comments.

unnecessary-pass (W0107)
    Unnecessary pass statement Used when a "pass" statement that can be avoided is encountered.

unreachable (W0101)
    Unreachable code Used when there is some code behind a "return" or "raise" statement, which will never be accessed.

eval-used (W0123)
    Use of eval Used when you use the "eval" function, to discourage its usage. Consider using ast.literal_eval for safely evaluating strings containing Python expressions from untrusted sources.

exec-used (W0122)
    Use of exec Raised when the 'exec' statement is used. It's dangerous to use this function for a user input, and it's also slower than actual code in general. This doesn't mean you should never use it, but you should consider alternatives first and restrict the functions available.

using-constant-test (W0125)
    Using a conditional statement with a constant value Emitted when a conditional statement (If or ternary if) uses a constant value for its test. This might not be what the user intended to do.

missing-parentheses-for-call-in-test (W0126)
    Using a conditional statement with potentially wrong function or method call due to missing parentheses Emitted when a conditional statement (If or ternary if) seems to wrongly call a function due to missing parentheses

comparison-of-constants (R0133)
    Comparison between constants: '%s %s %s' has a constant value When two literals are compared with each other the result is a constant. Using the constant directly is both easier to read and more performant. Initializing 'True' and 'False' this way is not required since Python 2.3.

literal-comparison (R0123)
    In '%s', use '%s' when comparing constant literals not '%s' ('%s') Used when comparing an object to a literal, which is usually what you do not want to do, since you can compare to a different literal than what was expected altogether.

comparison-with-itself (R0124)
    Redundant comparison - %s Used when something is compared against itself.

invalid-name (C0103)
    %s name "%s" doesn't conform to %s Used when the name doesn't conform to naming rules associated to its type (constant, variable, class...).

singleton-comparison (C0121)
    Comparison %s should be %s Used when an expression is compared to singleton values like True, False or None.

disallowed-name (C0104)
    Disallowed name "%s" Used when the name matches bad-names or bad-names-rgxs- (unauthorized names).

empty-docstring (C0112)
    Empty %s docstring Used when a module, function, class or method has an empty docstring (it would be too easy ;).

missing-class-docstring (C0115)
    Missing class docstring Used when a class has no docstring. Even an empty class must have a docstring.

missing-function-docstring (C0116)
    Missing function or method docstring Used when a function or method has no docstring. Some special methods like __init__ do not require a docstring.

missing-module-docstring (C0114)
    Missing module docstring Used when a module has no docstring. Empty modules do not require a docstring.

typevar-name-incorrect-variance (C0105)
    Type variable name does not reflect variance%s Emitted when a TypeVar name doesn't reflect its type variance. According to PEP8, it is recommended to add suffixes '_co' and '_contra' to the variables used to declare covariant or contravariant behaviour respectively. Invariant (default) variables do not require a suffix. The message is also emitted when invariant variables do have a suffix.

typevar-double-variance (C0131)
    TypeVar cannot be both covariant and contravariant Emitted when both the "covariant" and "contravariant" keyword arguments are set to "True" in a TypeVar.

typevar-name-mismatch (C0132)
    TypeVar name "%s" does not match assigned variable name "%s" Emitted when a TypeVar is assigned to a variable that does not match its name argument.

unidiomatic-typecheck (C0123)
    Use isinstance() rather than type() for a typecheck. The idiomatic way to perform an explicit typecheck in Python is to use isinstance(x, Y) rather than type(x) == Y, type(x) is Y. Though there are unusual situations where these give different results.

  Basic checker Reports

RP0101
    Statistics by type

  Classes checker

Verbatim name of the checker is classes.

See also classes checker's options' documentation

  Classes checker Messages

access-member-before-definition (E0203)
    Access to member %r before its definition line %s Used when an instance member is accessed before it's actually assigned.

method-hidden (E0202)
    An attribute defined in %s line %s hides this method Used when a class defines a method which is hidden by an instance attribute from an ancestor class or set by some client code.

assigning-non-slot (E0237)
    Assigning to attribute %r not defined in class slots Used when assigning to an attribute not defined in the class slots.

duplicate-bases (E0241)
    Duplicate bases for class %r Duplicate use of base classes in derived classes raise TypeErrors.

invalid-enum-extension (E0244)
    Extending inherited Enum class "%s" Used when a class tries to extend an inherited Enum class. Doing so will raise a TypeError at runtime.

inconsistent-mro (E0240)
    Inconsistent method resolution order for class %r Used when a class has an inconsistent method resolution order.

inherit-non-class (E0239)
    Inheriting %r, which is not a class. Used when a class inherits from something which is not a class.

invalid-slots (E0238)
    Invalid __slots__ object Used when an invalid __slots__ is found in class. Only a string, an iterable or a sequence is permitted.

invalid-class-object (E0243)
    Invalid assignment to '__class__'. Should be a class definition but got a '%s' Used when an invalid object is assigned to a __class__ property. Only a class is permitted.

invalid-slots-object (E0236)
    Invalid object %r in __slots__, must contain only non empty strings Used when an invalid (non-string) object occurs in __slots__.

no-method-argument (E0211)
    Method %r has no argument Used when a method which should have the bound instance as first argument has no argument defined.

no-self-argument (E0213)
    Method %r should have "self" as first argument Used when a method has an attribute different the "self" as first argument. This is considered as an error since this is a so common convention that you shouldn't break it!

unexpected-special-method-signature (E0302)
    The special method %r expects %s param(s), %d %s given Emitted when a special method was defined with an invalid number of parameters. If it has too few or too many, it might not work at all.

class-variable-slots-conflict (E0242)
    Value %r in slots conflicts with class variable Used when a value in __slots__ conflicts with a class variable, property or method.

invalid-bool-returned (E0304)
    __bool__ does not return bool Used when a __bool__ method returns something which is not a bool

invalid-bytes-returned (E0308)
    __bytes__ does not return bytes Used when a __bytes__ method returns something which is not bytes

invalid-format-returned (E0311)
    __format__ does not return str Used when a __format__ method returns something which is not a string

invalid-getnewargs-returned (E0312)
    __getnewargs__ does not return a tuple Used when a __getnewargs__ method returns something which is not a tuple

invalid-getnewargs-ex-returned (E0313)
    __getnewargs_ex__ does not return a tuple containing (tuple, dict) Used when a __getnewargs_ex__ method returns something which is not of the form tuple(tuple, dict)

invalid-hash-returned (E0309)
    __hash__ does not return int Used when a __hash__ method returns something which is not an integer

invalid-index-returned (E0305)
    __index__ does not return int Used when an __index__ method returns something which is not an integer

non-iterator-returned (E0301)
    __iter__ returns non-iterator Used when an __iter__ method returns something which is not an iterable (i.e. has no __next__ method)

invalid-length-returned (E0303)
    __len__ does not return non-negative integer Used when a __len__ method returns something which is not a non-negative integer

invalid-length-hint-returned (E0310)
    __length_hint__ does not return non-negative integer Used when a __length_hint__ method returns something which is not a non- negative integer

invalid-repr-returned (E0306)
    __repr__ does not return str Used when a __repr__ method returns something which is not a string

invalid-str-returned (E0307)
    __str__ does not return str Used when a __str__ method returns something which is not a string

arguments-differ (W0221)
    %s %s %r method Used when a method has a different number of arguments than in the implemented interface or in an overridden method. Extra arguments with default values are ignored.

arguments-renamed (W0237)
    %s %s %r method Used when a method parameter has a different name than in the implemented interface or in an overridden method.

protected-access (W0212)
    Access to a protected member %s of a client class Used when a protected member (i.e. class member with a name beginning with an underscore) is access outside the class or a descendant of the class where it's defined.

attribute-defined-outside-init (W0201)
    Attribute %r defined outside __init__ Used when an instance attribute is defined outside the __init__ method.

subclassed-final-class (W0240)
    Class %r is a subclass of a class decorated with typing.final: %r Used when a class decorated with typing.final has been subclassed.

implicit-flag-alias (W0213)
    Flag member %(overlap)s shares bit positions with %(sources)s Used when multiple integer values declared within an enum.IntFlag class share a common bit position.

abstract-method (W0223)
    Method %r is abstract in class %r but is not overridden in child class %r Used when an abstract method (i.e. raise NotImplementedError) is not overridden in concrete class.

overridden-final-method (W0239)
    Method %r overrides a method decorated with typing.final which is defined in class %r Used when a method decorated with typing.final has been overridden.

invalid-overridden-method (W0236)
    Method %r was expected to be %r, found it instead as %r Used when we detect that a method was overridden in a way that does not match its base class which could result in potential bugs at runtime.

redefined-slots-in-subclass (W0244)
    Redefined slots %r in subclass Used when a slot is re-defined in a subclass.

signature-differs (W0222)
    Signature differs from %s %r method Used when a method signature is different than in the implemented interface or in an overridden method.

bad-staticmethod-argument (W0211)
    Static method with %r as first argument Used when a static method has "self" or a value specified in valid- classmethod-first-arg option or valid-metaclass-classmethod-first-arg option as first argument.

super-without-brackets (W0245)
    Super call without brackets Used when a call to super does not have brackets and thus is not an actual call and does not work as expected.

unused-private-member (W0238)
    Unused private member `%s.%s` Emitted when a private member of a class is defined but not used.

useless-parent-delegation (W0246)
    Useless parent or super() delegation in method %r Used whenever we can detect that an overridden method is useless, relying on parent or super() delegation to do the same thing as another method from the MRO.

non-parent-init-called (W0233)
    __init__ method from a non direct base class %r is called Used when an __init__ method is called on a class which is not in the direct ancestors for the analysed class.

super-init-not-called (W0231)
    __init__ method from base class %r is not called Used when an ancestor class method has an __init__ method which is not called by a derived class.

property-with-parameters (R0206)
    Cannot have defined parameters for properties Used when we detect that a property also has parameters, which are useless, given that properties cannot be called with additional arguments.

useless-object-inheritance (R0205)
    Class %r inherits from object, can be safely removed from bases in python3 Used when a class inherit from object, which under python3 is implicit, hence can be safely removed from bases.

no-classmethod-decorator (R0202)
    Consider using a decorator instead of calling classmethod Used when a class method is defined without using the decorator syntax.

no-staticmethod-decorator (R0203)
    Consider using a decorator instead of calling staticmethod Used when a static method is defined without using the decorator syntax.

single-string-used-for-slots (C0205)
    Class __slots__ should be a non-string iterable Used when a class __slots__ is a simple string, rather than an iterable.

bad-classmethod-argument (C0202)
    Class method %s should have %s as first argument Used when a class method has a first argument named differently than the value specified in valid-classmethod-first-arg option (default to "cls"), recommended to easily differentiate them from regular instance methods.

bad-mcs-classmethod-argument (C0204)
    Metaclass class method %s should have %s as first argument Used when a metaclass class method has a first argument named differently than the value specified in valid-metaclass-classmethod-first-arg option (default to "mcs"), recommended to easily differentiate them from regular instance methods.

bad-mcs-method-argument (C0203)
    Metaclass method %s should have %s as first argument Used when a metaclass method has a first argument named differently than the value specified in valid-classmethod-first-arg option (default to "cls"), recommended to easily differentiate them from regular instance methods.

method-check-failed (F0202)
    Unable to check methods signature (%s / %s) Used when Pylint has been unable to check methods signature compatibility for an unexpected reason. Please report this kind if you don't make sense of it.

  Design checker

Verbatim name of the checker is design.

See also design checker's options' documentation

  Design checker Messages

too-few-public-methods (R0903)
    Too few public methods (%s/%s) Used when class has too few public methods, so be sure it's really worth it.

too-many-ancestors (R0901)
    Too many ancestors (%s/%s) Used when class has too many parent classes, try to reduce this to get a simpler (and so easier to use) class.

too-many-arguments (R0913)
    Too many arguments (%s/%s) Used when a function or method takes too many arguments.

too-many-boolean-expressions (R0916)
    Too many boolean expressions in if statement (%s/%s) Used when an if statement contains too many boolean expressions.

too-many-branches (R0912)
    Too many branches (%s/%s) Used when a function or method has too many branches, making it hard to follow.

too-many-instance-attributes (R0902)
    Too many instance attributes (%s/%s) Used when class has too many instance attributes, try to reduce this to get a simpler (and so easier to use) class.

too-many-locals (R0914)
    Too many local variables (%s/%s) Used when a function or method has too many local variables.

too-many-public-methods (R0904)
    Too many public methods (%s/%s) Used when class has too many public methods, try to reduce this to get a simpler (and so easier to use) class.

too-many-return-statements (R0911)
    Too many return statements (%s/%s) Used when a function or method has too many return statement, making it hard to follow.

too-many-statements (R0915)
    Too many statements (%s/%s) Used when a function or method has too many statements. You should then split it in smaller functions / methods.

  Exceptions checker

Verbatim name of the checker is exceptions.

See also exceptions checker's options' documentation

  Exceptions checker Messages

bad-except-order (E0701)
    Bad except clauses order (%s) Used when except clauses are not in the correct order (from the more specific to the more generic). If you don't fix the order, some exceptions may not be caught by the most specific handler.

catching-non-exception (E0712)
    Catching an exception which doesn't inherit from Exception: %s Used when a class which doesn't inherit from Exception is used as an exception in an except clause.

bad-exception-cause (E0705)
    Exception cause set to something which is not an exception, nor None Used when using the syntax "raise ... from ...", where the exception cause is not an exception, nor None.

notimplemented-raised (E0711)
    NotImplemented raised - should raise NotImplementedError Used when NotImplemented is raised instead of NotImplementedError

raising-bad-type (E0702)
    Raising %s while only classes or instances are allowed Used when something which is neither a class nor an instance is raised (i.e. a TypeError will be raised).

raising-non-exception (E0710)
    Raising a new style class which doesn't inherit from BaseException Used when a new style class which doesn't inherit from BaseException is raised.

misplaced-bare-raise (E0704)
    The raise statement is not inside an except clause Used when a bare raise is not used inside an except clause. This generates an error, since there are no active exceptions to be reraised. An exception to this rule is represented by a bare raise inside a finally clause, which might work, as long as an exception is raised inside the try block, but it is nevertheless a code smell that must not be relied upon.

duplicate-except (W0705)
    Catching previously caught exception type %s Used when an except catches a type that was already caught by a previous handler.

broad-exception-caught (W0718)
    Catching too general exception %s If you use a naked except Exception: clause, you might end up catching exceptions other than the ones you expect to catch. This can hide bugs or make it harder to debug programs when unrelated errors are hidden.

raise-missing-from (W0707)
    Consider explicitly re-raising using %s'%s from %s' Python's exception chaining shows the traceback of the current exception, but also of the original exception. When you raise a new exception after another exception was caught it's likely that the second exception is a friendly re- wrapping of the first exception. In such cases raise from provides a better link between the two tracebacks in the final error.

raising-format-tuple (W0715)
    Exception arguments suggest string formatting might be intended Used when passing multiple arguments to an exception constructor, the first of them a string literal containing what appears to be placeholders intended for formatting

binary-op-exception (W0711)
    Exception to catch is the result of a binary "%s" operation Used when the exception to catch is of the form "except A or B:". If intending to catch multiple, rewrite as "except (A, B):"

wrong-exception-operation (W0716)
    Invalid exception operation. %s Used when an operation is done against an exception, but the operation is not valid for the exception in question. Usually emitted when having binary operations between exceptions in except handlers.

bare-except (W0702)
    No exception type(s) specified A bare except: clause will catch SystemExit and KeyboardInterrupt exceptions, making it harder to interrupt a program with Control-C, and can disguise other problems. If you want to catch all exceptions that signal program errors, use except Exception: (bare except is equivalent to except BaseException:).

broad-exception-raised (W0719)
    Raising too general exception: %s Raising exceptions that are too generic force you to catch exceptions generically too. It will force you to use a naked except Exception: clause. You might then end up catching exceptions other than the ones you expect to catch. This can hide bugs or make it harder to debug programs when unrelated errors are hidden.

try-except-raise (W0706)
    The except handler raises immediately Used when an except handler uses raise as its first or only operator. This is useless because it raises back the exception immediately. Remove the raise operator or the entire try-except-raise block!

  Format checker

Verbatim name of the checker is format.

See also format checker's options' documentation

  Format checker Messages

bad-indentation (W0311)
    Bad indentation. Found %s %s, expected %s Used when an unexpected number of indentation's tabulations or spaces has been found.

unnecessary-semicolon (W0301)
    Unnecessary semicolon Used when a statement is ended by a semi-colon (";"), which isn't necessary (that's python, not C ;).

missing-final-newline (C0304)
    Final newline missing Used when the last line in a file is missing a newline.

line-too-long (C0301)
    Line too long (%s/%s) Used when a line is longer than a given number of characters.

mixed-line-endings (C0327)
    Mixed line endings LF and CRLF Used when there are mixed (LF and CRLF) newline signs in a file.

multiple-statements (C0321)
    More than one statement on a single line Used when more than on statement are found on the same line.

too-many-lines (C0302)
    Too many lines in module (%s/%s) Used when a module has too many lines, reducing its readability.

trailing-newlines (C0305)
    Trailing newlines Used when there are trailing blank lines in a file.

trailing-whitespace (C0303)
    Trailing whitespace Used when there is whitespace between the end of a line and the newline.

unexpected-line-ending-format (C0328)
    Unexpected line ending format. There is '%s' while it should be '%s'. Used when there is different newline than expected.

superfluous-parens (C0325)
    Unnecessary parens after %r keyword Used when a single item in parentheses follows an if, for, or other keyword.

  Imports checker

Verbatim name of the checker is imports.

See also imports checker's options' documentation

  Imports checker Messages

relative-beyond-top-level (E0402)
    Attempted relative import beyond top-level package Used when a relative import tries to access too many levels in the current package.

import-error (E0401)
    Unable to import %s Used when pylint has been unable to import a module.

deprecated-module (W4901)
    Deprecated module %r A module marked as deprecated is imported.

import-self (W0406)
    Module import itself Used when a module is importing itself.

preferred-module (W0407)
    Prefer importing %r instead of %r Used when a module imported has a preferred replacement module.

reimported (W0404)
    Reimport %r (imported line %s) Used when a module is imported more than once.

shadowed-import (W0416)
    Shadowed %r (imported line %s) Used when a module is aliased with a name that shadows another import.

wildcard-import (W0401)
    Wildcard import %s Used when from module import * is detected.

misplaced-future (W0410)
    __future__ import is not the first non docstring statement Python 2.5 and greater require __future__ import to be the first non docstring statement in the module.

cyclic-import (R0401)
    Cyclic import (%s) Used when a cyclic import between two or more modules is detected.

consider-using-from-import (R0402)
    Use 'from %s import %s' instead Emitted when a submodule of a package is imported and aliased with the same name, e.g., instead of import concurrent.futures as futures use from concurrent import futures.

wrong-import-order (C0411)
    %s should be placed before %s Used when PEP8 import order is not respected (standard imports first, then third-party libraries, then local imports).

wrong-import-position (C0413)
    Import "%s" should be placed at the top of the module Used when code and imports are mixed.

useless-import-alias (C0414)
    Import alias does not rename original package Used when an import alias is same as original package, e.g., using import numpy as numpy instead of import numpy as np.

import-outside-toplevel (C0415)
    Import outside toplevel (%s) Used when an import statement is used anywhere other than the module toplevel. Move this import to the top of the file.

ungrouped-imports (C0412)
    Imports from package %s are not grouped Used when imports are not grouped by packages.

multiple-imports (C0410)
    Multiple imports on one line (%s) Used when import statement importing multiple modules is detected.

  Imports checker Reports

RP0401
    External dependencies

RP0402
    Modules dependencies graph

  Lambda-Expressions checker

Verbatim name of the checker is lambda-expressions.

  Lambda-Expressions checker Messages

unnecessary-lambda-assignment (C3001)
    Lambda expression assigned to a variable. Define a function using the "def" keyword instead. Used when a lambda expression is assigned to variable rather than defining a standard function with the "def" keyword.

unnecessary-direct-lambda-call (C3002)
    Lambda expression called directly. Execute the expression inline instead. Used when a lambda expression is directly called rather than executing its contents inline.

  Logging checker

Verbatim name of the checker is logging.

See also logging checker's options' documentation

  Logging checker Messages

logging-format-truncated (E1201)
    Logging format string ends in middle of conversion specifier Used when a logging statement format string terminates before the end of a conversion specifier.

logging-too-few-args (E1206)
    Not enough arguments for logging format string Used when a logging format string is given too few arguments.

logging-too-many-args (E1205)
    Too many arguments for logging format string Used when a logging format string is given too many arguments.

logging-unsupported-format (E1200)
    Unsupported logging format character %r (%#02x) at index %d Used when an unsupported format character is used in a logging statement format string.

logging-format-interpolation (W1202)
    Use %s formatting in logging functions Used when a logging statement has a call form of "logging.<logging method>(format_string.format(format_args...))". Use another type of string formatting instead. You can use % formatting but leave interpolation to the logging function by passing the parameters as arguments. If logging-fstring- interpolation is disabled then you can use fstring formatting. If logging- not-lazy is disabled then you can use % formatting as normal.

logging-fstring-interpolation (W1203)
    Use %s formatting in logging functions Used when a logging statement has a call form of "logging.<logging method>(f"...")".Use another type of string formatting instead. You can use % formatting but leave interpolation to the logging function by passing the parameters as arguments. If logging-format-interpolation is disabled then you can use str.format. If logging-not-lazy is disabled then you can use % formatting as normal.

logging-not-lazy (W1201)
    Use %s formatting in logging functions Used when a logging statement has a call form of "logging.<logging method>(format_string % (format_args...))". Use another type of string formatting instead. You can use % formatting but leave interpolation to the logging function by passing the parameters as arguments. If logging-fstring- interpolation is disabled then you can use fstring formatting. If logging- format-interpolation is disabled then you can use str.format.

  Method Args checker

Verbatim name of the checker is method_args.

See also method_args checker's options' documentation

  Method Args checker Messages

positional-only-arguments-expected (E3102)
    `%s()` got some positional-only arguments passed as keyword arguments: %s Emitted when positional-only arguments have been passed as keyword arguments. Remove the keywords for the affected arguments in the function call. This message can't be emitted when using Python < 3.8.

missing-timeout (W3101)
    Missing timeout argument for method '%s' can cause your program to hang indefinitely Used when a method needs a 'timeout' parameter in order to avoid waiting for a long time. If no timeout is specified explicitly the default value is used. For example for 'requests' the program will never time out (i.e. hang indefinitely).

  Metrics checker

Verbatim name of the checker is metrics.

  Metrics checker Reports

RP0701
    Raw metrics

  Miscellaneous checker

Verbatim name of the checker is miscellaneous.

See also miscellaneous checker's options' documentation

  Miscellaneous checker Messages

fixme (W0511)
    Used when a warning note as FIXME or XXX is detected.

use-symbolic-message-instead (I0023)
    Used when a message is enabled or disabled by id.

  Modified Iteration checker

Verbatim name of the checker is modified_iteration.

  Modified Iteration checker Messages

modified-iterating-dict (E4702)
    Iterated dict '%s' is being modified inside for loop body, iterate through a copy of it instead. Emitted when items are added or removed to a dict being iterated through. Doing so raises a RuntimeError.

modified-iterating-set (E4703)
    Iterated set '%s' is being modified inside for loop body, iterate through a copy of it instead. Emitted when items are added or removed to a set being iterated through. Doing so raises a RuntimeError.

modified-iterating-list (W4701)
    Iterated list '%s' is being modified inside for loop body, consider iterating through a copy of it instead. Emitted when items are added or removed to a list being iterated through. Doing so can result in unexpected behaviour, that is why it is preferred to use a copy of the list.

  Nested Min Max checker

Verbatim name of the checker is nested_min_max.

  Nested Min Max checker Messages

nested-min-max (W3301)
    Do not use nested call of '%s'; it's possible to do '%s' instead Nested calls min(1, min(2, 3)) can be rewritten as min(1, 2, 3).

  Newstyle checker

Verbatim name of the checker is newstyle.

  Newstyle checker Messages

bad-super-call (E1003)
    Bad first argument %r given to super() Used when another argument than the current class is given as first argument of the super builtin.

  Nonascii-Checker checker

Verbatim name of the checker is nonascii-checker.

  Nonascii-Checker checker Messages

non-ascii-file-name (W2402)
    %s name "%s" contains a non-ASCII character. Under python 3.5, PEP 3131 allows non-ascii identifiers, but not non-ascii file names.Since Python 3.5, even though Python supports UTF-8 files, some editors or tools don't.

non-ascii-name (C2401)
    %s name "%s" contains a non-ASCII character, consider renaming it. Used when the name contains at least one non-ASCII unicode character. See https://peps.python.org/pep-0672/#confusing-features for a background why this could be bad. If your programming guideline defines that you are programming in English, then there should be no need for non ASCII characters in Python Names. If not you can simply disable this check.

non-ascii-module-import (C2403)
    %s name "%s" contains a non-ASCII character, use an ASCII-only alias for import. Used when the name contains at least one non-ASCII unicode character. See https://peps.python.org/pep-0672/#confusing-features for a background why this could be bad. If your programming guideline defines that you are programming in English, then there should be no need for non ASCII characters in Python Names. If not you can simply disable this check.

  Refactoring checker

Verbatim name of the checker is refactoring.

See also refactoring checker's options' documentation

  Refactoring checker Messages

simplifiable-condition (R1726)
    Boolean condition '%s' may be simplified to '%s' Emitted when a boolean condition is able to be simplified.

condition-evals-to-constant (R1727)
    Boolean condition '%s' will always evaluate to '%s' Emitted when a boolean condition can be simplified to a constant value.

simplify-boolean-expression (R1709)
    Boolean expression may be simplified to %s Emitted when redundant pre-python 2.5 ternary syntax is used.

consider-using-in (R1714)
    Consider merging these comparisons with 'in' by using '%s %sin (%s)'. Use a set instead if elements are hashable. To check if a variable is equal to one of many values, combine the values into a set or tuple and check if the variable is contained "in" it instead of checking for equality against each of the values. This is faster and less verbose.

consider-merging-isinstance (R1701)
    Consider merging these isinstance calls to isinstance(%s, (%s)) Used when multiple consecutive isinstance calls can be merged into one.

use-dict-literal (R1735)
    Consider using '%s' instead of a call to 'dict'. Emitted when using dict() to create a dictionary instead of a literal '{ ... }'. The literal is faster as it avoids an additional function call.

consider-using-max-builtin (R1731)
    Consider using '%s' instead of unnecessary if block Using the max builtin instead of a conditional improves readability and conciseness.

consider-using-min-builtin (R1730)
    Consider using '%s' instead of unnecessary if block Using the min builtin instead of a conditional improves readability and conciseness.

consider-using-sys-exit (R1722)
    Consider using 'sys.exit' instead Contrary to 'exit()' or 'quit()', 'sys.exit' does not rely on the site module being available (as the 'sys' module is always available).

consider-using-with (R1732)
    Consider using 'with' for resource-allocating operations Emitted if a resource-allocating assignment or call may be replaced by a 'with' block. By using 'with' the release of the allocated resources is ensured even in the case of an exception.

super-with-arguments (R1725)
    Consider using Python 3 style super() without arguments Emitted when calling the super() builtin with the current class and instance. On Python 3 these arguments are the default and they can be omitted.

use-list-literal (R1734)
    Consider using [] instead of list() Emitted when using list() to create an empty list instead of the literal []. The literal is faster as it avoids an additional function call.

consider-using-dict-comprehension (R1717)
    Consider using a dictionary comprehension Emitted when we detect the creation of a dictionary using the dict() callable and a transient list. Although there is nothing syntactically wrong with this code, it is hard to read and can be simplified to a dict comprehension. Also it is faster since you don't need to create another transient list

consider-using-generator (R1728)
    Consider using a generator instead '%s(%s)' If your container can be large using a generator will bring better performance.

consider-using-set-comprehension (R1718)
    Consider using a set comprehension Although there is nothing syntactically wrong with this code, it is hard to read and can be simplified to a set comprehension. Also it is faster since you don't need to create another transient list

consider-using-get (R1715)
    Consider using dict.get for getting values from a dict if a key is present or a default if not Using the builtin dict.get for getting a value from a dictionary if a key is present or a default if not, is simpler and considered more idiomatic, although sometimes a bit slower

consider-using-join (R1713)
    Consider using str.join(sequence) for concatenating strings from an iterable Using str.join(sequence) is faster, uses less memory and increases readability compared to for-loop iteration.

consider-using-ternary (R1706)
    Consider using ternary (%s) Used when one of known pre-python 2.5 ternary syntax is used.

consider-swap-variables (R1712)
    Consider using tuple unpacking for swapping variables You do not have to use a temporary variable in order to swap variables. Using "tuple unpacking" to directly swap variables makes the intention more clear.

trailing-comma-tuple (R1707)
    Disallow trailing comma tuple In Python, a tuple is actually created by the comma symbol, not by the parentheses. Unfortunately, one can actually create a tuple by misplacing a trailing comma, which can lead to potential weird bugs in your code. You should always use parentheses explicitly for creating a tuple.

stop-iteration-return (R1708)
    Do not raise StopIteration in generator, use return statement instead According to PEP479, the raise of StopIteration to end the loop of a generator may lead to hard to find bugs. This PEP specify that raise StopIteration has to be replaced by a simple return statement

inconsistent-return-statements (R1710)
    Either all return statements in a function should return an expression, or none of them should. According to PEP8, if any return statement returns an expression, any return statements where no value is returned should explicitly state this as return None, and an explicit return statement should be present at the end of the function (if reachable)

redefined-argument-from-local (R1704)
    Redefining argument with the local name %r Used when a local name is redefining an argument, which might suggest a potential error. This is taken in account only for a handful of name binding operations, such as for iteration, with statement assignment and exception handler assignment.

chained-comparison (R1716)
    Simplify chained comparison between the operands This message is emitted when pylint encounters boolean operation like "a < b and b < c", suggesting instead to refactor it to "a < b < c"

simplifiable-if-expression (R1719)
    The if expression can be replaced with %s Used when an if expression can be replaced with 'bool(test)' or simply 'test' if the boolean cast is implicit.

simplifiable-if-statement (R1703)
    The if statement can be replaced with %s Used when an if statement can be replaced with 'bool(test)'.

too-many-nested-blocks (R1702)
    Too many nested blocks (%s/%s) Used when a function or a method has too many nested blocks. This makes the code less understandable and maintainable.

no-else-break (R1723)
    Unnecessary "%s" after "break", %s Used in order to highlight an unnecessary block of code following an if containing a break statement. As such, it will warn when it encounters an else following a chain of ifs, all of them containing a break statement.

no-else-continue (R1724)
    Unnecessary "%s" after "continue", %s Used in order to highlight an unnecessary block of code following an if containing a continue statement. As such, it will warn when it encounters an else following a chain of ifs, all of them containing a continue statement.

no-else-raise (R1720)
    Unnecessary "%s" after "raise", %s Used in order to highlight an unnecessary block of code following an if containing a raise statement. As such, it will warn when it encounters an else following a chain of ifs, all of them containing a raise statement.

no-else-return (R1705)
    Unnecessary "%s" after "return", %s Used in order to highlight an unnecessary block of code following an if containing a return statement. As such, it will warn when it encounters an else following a chain of ifs, all of them containing a return statement.

unnecessary-dict-index-lookup (R1733)
    Unnecessary dictionary index lookup, use '%s' instead Emitted when iterating over the dictionary items (key-item pairs) and accessing the value by index lookup. The value can be accessed directly instead.

unnecessary-list-index-lookup (R1736)
    Unnecessary list index lookup, use '%s' instead Emitted when iterating over an enumeration and accessing the value by index lookup. The value can be accessed directly instead.

unnecessary-comprehension (R1721)
    Unnecessary use of a comprehension, use %s instead. Instead of using an identity comprehension, consider using the list, dict or set constructor. It is faster and simpler.

use-a-generator (R1729)
    Use a generator instead '%s(%s)' Comprehension inside of 'any', 'all', 'max', 'min' or 'sum' is unnecessary. A generator would be sufficient and faster.

useless-return (R1711)
    Useless return at end of function or method Emitted when a single "return" or "return None" statement is found at the end of function or method definition. This statement can safely be removed because Python will implicitly return None

use-implicit-booleaness-not-comparison (C1803)
    '%s' can be simplified to '%s' as an empty %s is falsey Used when Pylint detects that collection literal comparison is being used to check for emptiness; Use implicit booleaness instead of a collection classes; empty collections are considered as false

unneeded-not (C0113)
    Consider changing "%s" to "%s" Used when a boolean expression contains an unneeded negation.

consider-iterating-dictionary (C0201)
    Consider iterating the dictionary directly instead of calling .keys() Emitted when the keys of a dictionary are iterated through the .keys() method or when .keys() is used for a membership check. It is enough to iterate through the dictionary itself, for key in dictionary. For membership checks, if key in dictionary is faster.

consider-using-dict-items (C0206)
    Consider iterating with .items() Emitted when iterating over the keys of a dictionary and accessing the value by index lookup. Both the key and value can be accessed by iterating using the .items() method of the dictionary instead.

consider-using-enumerate (C0200)
    Consider using enumerate instead of iterating with range and len Emitted when code that iterates with range and len is encountered. Such code can be simplified by using the enumerate builtin.

use-implicit-booleaness-not-len (C1802)
    Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty Used when Pylint detects that len(sequence) is being used without explicit comparison inside a condition to determine if a sequence is empty. Instead of coercing the length to a boolean, either rely on the fact that empty sequences are false or compare the length against a scalar.

consider-using-f-string (C0209)
    Formatting a regular string which could be a f-string Used when we detect a string that is being formatted with format() or % which could potentially be a f-string. The use of f-strings is preferred. Requires Python 3.6 and py-version >= 3.6.

use-maxsplit-arg (C0207)
    Use %s instead Emitted when accessing only the first or last element of str.split(). The first and last element can be accessed by using str.split(sep, maxsplit=1)[0] or str.rsplit(sep, maxsplit=1)[-1] instead.

use-sequence-for-iteration (C0208)
    Use a sequence type when iterating over values When iterating over values, sequence types (e.g., lists, tuples, ranges) are more efficient than sets.

  Similarities checker

Verbatim name of the checker is similarities.

See also similarities checker's options' documentation

  Similarities checker Messages

duplicate-code (R0801)
    Similar lines in %s files Indicates that a set of similar lines has been detected among multiple file. This usually means that the code should be refactored to avoid this duplication.

  Similarities checker Reports

RP0801
    Duplication

  Spelling checker

Verbatim name of the checker is spelling.

See also spelling checker's options' documentation

  Spelling checker Messages

invalid-characters-in-docstring (C0403)
    Invalid characters %r in a docstring Used when a word in docstring cannot be checked by enchant.

wrong-spelling-in-comment (C0401)
    Wrong spelling of a word '%s' in a comment: Used when a word in comment is not spelled correctly.

wrong-spelling-in-docstring (C0402)
    Wrong spelling of a word '%s' in a docstring: Used when a word in docstring is not spelled correctly.

  Stdlib checker

Verbatim name of the checker is stdlib.

  Stdlib checker Messages

invalid-envvar-value (E1507)
    %s does not support %s type argument Env manipulation functions support only string type arguments. See https://docs.python.org/3/library/os.html#os.getenv.

singledispatch-method (E1519)
    singledispatch decorator should not be used with methods, use singledispatchmethod instead. singledispatch should decorate functions and not class/instance methods. Use singledispatchmethod for those cases.

singledispatchmethod-function (E1520)
    singledispatchmethod decorator should not be used with functions, use singledispatch instead. singledispatchmethod should decorate class/instance methods and not functions. Use singledispatch for those cases.

bad-open-mode (W1501)
    "%s" is not a valid mode for open. Python supports: r, w, a[, x] modes with b, +, and U (only with r) options. See https://docs.python.org/3/library/functions.html#open

invalid-envvar-default (W1508)
    %s default type is %s. Expected str or None. Env manipulation functions return None or str values. Supplying anything different as a default may cause bugs. See https://docs.python.org/3/library/os.html#os.getenv.

method-cache-max-size-none (W1518)
    'lru_cache(maxsize=None)' or 'cache' will keep all method args alive indefinitely, including 'self' By decorating a method with lru_cache or cache the 'self' argument will be linked to the function and therefore never garbage collected. Unless your instance will never need to be garbage collected (singleton) it is recommended to refactor code to avoid this pattern or add a maxsize to the cache. The default value for maxsize is 128.

subprocess-run-check (W1510)
    'subprocess.run' used without explicitly defining the value for 'check'. The check keyword is set to False by default. It means the process launched by subprocess.run can exit with a non-zero exit code and fail silently. It's better to set it explicitly to make clear what the error- handling behavior is.

forgotten-debug-statement (W1515)
    Leaving functions creating breakpoints in production code is not recommended Calls to breakpoint(), sys.breakpointhook() and pdb.set_trace() should be removed from code that is not actively being debugged.

redundant-unittest-assert (W1503)
    Redundant use of %s with constant value %r The first argument of assertTrue and assertFalse is a condition. If a constant is passed as parameter, that condition will be always true. In this case a warning should be emitted.

shallow-copy-environ (W1507)
    Using copy.copy(os.environ). Use os.environ.copy() instead. os.environ is not a dict object but proxy object, so shallow copy has still effects on original object. See https://bugs.python.org/issue15373 for reference.

boolean-datetime (W1502)
    Using datetime.time in a boolean context. Using datetime.time in a boolean context can hide subtle bugs when the time they represent matches midnight UTC. This behaviour was fixed in Python 3.5. See https://bugs.python.org/issue13936 for reference. This message can't be emitted when using Python >= 3.5.

deprecated-argument (W4903)
    Using deprecated argument %s of method %s() The argument is marked as deprecated and will be removed in the future.

deprecated-class (W4904)
    Using deprecated class %s of module %s The class is marked as deprecated and will be removed in the future.

deprecated-decorator (W4905)
    Using deprecated decorator %s() The decorator is marked as deprecated and will be removed in the future.

deprecated-method (W4902)
    Using deprecated method %s() The method is marked as deprecated and will be removed in the future.

unspecified-encoding (W1514)
    Using open without explicitly specifying an encoding It is better to specify an encoding when opening documents. Using the system default implicitly can create problems on other operating systems. See https://peps.python.org/pep-0597/

subprocess-popen-preexec-fn (W1509)
    Using preexec_fn keyword which may be unsafe in the presence of threads The preexec_fn parameter is not safe to use in the presence of threads in your application. The child process could deadlock before exec is called. If you must use it, keep it trivial! Minimize the number of libraries you call into. See https://docs.python.org/3/library/subprocess.html#popen-constructor

bad-thread-instantiation (W1506)
    threading.Thread needs the target function The warning is emitted when a threading.Thread class is instantiated without the target function being passed as a kwarg or as a second argument. By default, the first parameter is the group param, not the target param.

  String checker

Verbatim name of the checker is string.

See also string checker's options' documentation

  String checker Messages

bad-string-format-type (E1307)
    Argument %r does not match format type %r Used when a type required by format string is not suitable for actual argument type

format-needs-mapping (E1303)
    Expected mapping for format string, not %s Used when a format string that uses named conversion specifiers is used with an argument that is not a mapping.

truncated-format-string (E1301)
    Format string ends in middle of conversion specifier Used when a format string terminates before the end of a conversion specifier.

missing-format-string-key (E1304)
    Missing key %r in format string dictionary Used when a format string that uses named conversion specifiers is used with a dictionary that doesn't contain all the keys required by the format string.

mixed-format-string (E1302)
    Mixing named and unnamed conversion specifiers in format string Used when a format string contains both named (e.g. '%(foo)d') and unnamed (e.g. '%d') conversion specifiers. This is also used when a named conversion specifier contains * for the minimum field width and/or precision.

too-few-format-args (E1306)
    Not enough arguments for format string Used when a format string that uses unnamed conversion specifiers is given too few arguments

bad-str-strip-call (E1310)
    Suspicious argument in %s.%s call The argument to a str.{l,r,}strip call contains a duplicate character,

too-many-format-args (E1305)
    Too many arguments for format string Used when a format string that uses unnamed conversion specifiers is given too many arguments.

bad-format-character (E1300)
    Unsupported format character %r (%#02x) at index %d Used when an unsupported format character is used in a format string.

anomalous-unicode-escape-in-string (W1402)
    Anomalous Unicode escape in byte string: '%s'. String constant might be missing an r or u prefix. Used when an escape like u is encountered in a byte string where it has no effect.

anomalous-backslash-in-string (W1401)
    Anomalous backslash in string: '%s'. String constant might be missing an r prefix. Used when a backslash is in a literal string but not as an escape.

duplicate-string-formatting-argument (W1308)
    Duplicate string formatting argument %r, consider passing as named argument Used when we detect that a string formatting is repeating an argument instead of using named string arguments

format-combined-specification (W1305)
    Format string contains both automatic field numbering and manual field specification Used when a PEP 3101 format string contains both automatic field numbering (e.g. '{}') and manual field specification (e.g. '{0}').

bad-format-string-key (W1300)
    Format string dictionary key should be a string, not %s Used when a format string that uses named conversion specifiers is used with a dictionary whose keys are not all strings.

implicit-str-concat (W1404)
    Implicit string concatenation found in %s String literals are implicitly concatenated in a literal iterable definition : maybe a comma is missing ?

bad-format-string (W1302)
    Invalid format string Used when a PEP 3101 format string is invalid.

missing-format-attribute (W1306)
    Missing format attribute %r in format specifier %r Used when a PEP 3101 format string uses an attribute specifier ({0.length}), but the argument passed for formatting doesn't have that attribute.

missing-format-argument-key (W1303)
    Missing keyword argument %r for format string Used when a PEP 3101 format string that uses named fields doesn't receive one or more required keywords.

inconsistent-quotes (W1405)
    Quote delimiter %s is inconsistent with the rest of the file Quote delimiters are not used consistently throughout a module (with allowances made for avoiding unnecessary escaping).

redundant-u-string-prefix (W1406)
    The u prefix for strings is no longer necessary in Python >=3.0 Used when we detect a string with a u prefix. These prefixes were necessary in Python 2 to indicate a string was Unicode, but since Python 3.0 strings are Unicode by default.

unused-format-string-argument (W1304)
    Unused format argument %r Used when a PEP 3101 format string that uses named fields is used with an argument that is not required by the format string.

unused-format-string-key (W1301)
    Unused key %r in format string dictionary Used when a format string that uses named conversion specifiers is used with a dictionary that contains keys not required by the format string.

f-string-without-interpolation (W1309)
    Using an f-string that does not have any interpolated variables Used when we detect an f-string that does not use any interpolation variables, in which case it can be either a normal string or a bug in the code.

format-string-without-interpolation (W1310)
    Using formatting for a string that does not have any interpolated variables Used when we detect a string that does not have any interpolation variables, in which case it can be either a normal string without formatting or a bug in the code.

invalid-format-index (W1307)
    Using invalid lookup key %r in format specifier %r Used when a PEP 3101 format string uses a lookup specifier ({a[1]}), but the argument passed for formatting doesn't contain or doesn't have that key as an attribute.

  Threading checker

Verbatim name of the checker is threading.

  Threading checker Messages

useless-with-lock (W2101)
    '%s()' directly created in 'with' has no effect Used when a new lock instance is created by using with statement which has no effect. Instead, an existing instance should be used to acquire lock.

  Typecheck checker

Verbatim name of the checker is typecheck.

See also typecheck checker's options' documentation

  Typecheck checker Messages

unsupported-assignment-operation (E1137)
    %r does not support item assignment Emitted when an object does not support item assignment (i.e. doesn't define __setitem__ method).

unsupported-delete-operation (E1138)
    %r does not support item deletion Emitted when an object does not support item deletion (i.e. doesn't define __delitem__ method).

invalid-unary-operand-type (E1130)
    Emitted when a unary operand is used on an object which does not support this type of operation.

unsupported-binary-operation (E1131)
    Emitted when a binary arithmetic operation between two operands is not supported.

no-member (E1101)
    %s %r has no %r member%s Used when a variable is accessed for a nonexistent member.

not-callable (E1102)
    %s is not callable Used when an object being called has been inferred to a non callable object.

unhashable-member (E1143)
    '%s' is unhashable and can't be used as a %s in a %s Emitted when a dict key or set member is not hashable (i.e. doesn't define __hash__ method).

await-outside-async (E1142)
    'await' should be used within an async function Emitted when await is used outside an async function.

redundant-keyword-arg (E1124)
    Argument %r passed by position and keyword in %s call Used when a function call would result in assigning multiple values to a function parameter, one value from a positional argument and one from a keyword argument.

assignment-from-no-return (E1111)
    Assigning result of a function call, where the function has no return Used when an assignment is done on a function call but the inferred function doesn't return anything.

assignment-from-none (E1128)
    Assigning result of a function call, where the function returns None Used when an assignment is done on a function call but the inferred function returns nothing but None.

not-context-manager (E1129)
    Context manager '%s' doesn't implement __enter__ and __exit__. Used when an instance in a with statement doesn't implement the context manager protocol(__enter__/__exit__).

repeated-keyword (E1132)
    Got multiple values for keyword argument %r in function call Emitted when a function call got multiple values for a keyword.

invalid-metaclass (E1139)
    Invalid metaclass %r used Emitted whenever we can detect that a class is using, as a metaclass, something which might be invalid for using as a metaclass.

missing-kwoa (E1125)
    Missing mandatory keyword argument %r in %s call Used when a function call does not pass a mandatory keyword-only argument.

no-value-for-parameter (E1120)
    No value for argument %s in %s call Used when a function call passes too few arguments.

not-an-iterable (E1133)
    Non-iterable value %s is used in an iterating context Used when a non-iterable value is used in place where iterable is expected

not-a-mapping (E1134)
    Non-mapping value %s is used in a mapping context Used when a non-mapping value is used in place where mapping is expected

invalid-sequence-index (E1126)
    Sequence index is not an int, slice, or instance with __index__ Used when a sequence type is indexed with an invalid type. Valid types are ints, slices, and objects with an __index__ method.

invalid-slice-index (E1127)
    Slice index is not an int, None, or instance with __index__ Used when a slice index is not an integer, None, or an object with an __index__ method.

invalid-slice-step (E1144)
    Slice step cannot be 0 Used when a slice step is 0 and the object doesn't implement a custom __getitem__ method.

too-many-function-args (E1121)
    Too many positional arguments for %s call Used when a function call passes too many positional arguments.

unexpected-keyword-arg (E1123)
    Unexpected keyword argument %r in %s call Used when a function call passes a keyword argument that doesn't correspond to one of the function's parameter names.

dict-iter-missing-items (E1141)
    Unpacking a dictionary in iteration without calling .items() Emitted when trying to iterate through a dict without calling .items()

unsupported-membership-test (E1135)
    Value '%s' doesn't support membership test Emitted when an instance in membership test expression doesn't implement membership protocol (__contains__/__iter__/__getitem__).

unsubscriptable-object (E1136)
    Value '%s' is unsubscriptable Emitted when a subscripted value doesn't support subscription (i.e. doesn't define __getitem__ method or __class_getitem__ for a class).

keyword-arg-before-vararg (W1113)
    Keyword argument before variable positional arguments list in the definition of %s function When defining a keyword argument before variable positional arguments, one can end up in having multiple values passed for the aforementioned parameter in case the method is called with keyword arguments.

non-str-assignment-to-dunder-name (W1115)
    Non-string value assigned to __name__ Emitted when a non-string value is assigned to __name__

arguments-out-of-order (W1114)
    Positional arguments appear to be out of order Emitted when the caller's argument names fully match the parameter names in the function signature but do not have the same order.

isinstance-second-argument-not-valid-type (W1116)
    Second argument of isinstance is not a type Emitted when the second argument of an isinstance call is not a type.

c-extension-no-member (I1101)
    %s %r has no %r member%s, but source is unavailable. Consider adding this module to extension-pkg-allow-list if you want to perform analysis based on run-time introspection of living objects. Used when a variable is accessed for non-existent member of C extension. Due to unavailability of source static analysis is impossible, but it may be performed by introspecting living objects in run-time.

  Unicode Checker checker

Verbatim name of the checker is unicode_checker.

  Unicode Checker checker Messages

bidirectional-unicode (E2502)
    Contains control characters that can permit obfuscated code executed differently than displayed bidirectional unicode are typically not displayed characters required to display right-to-left (RTL) script (i.e. Chinese, Japanese, Arabic, Hebrew, ...) correctly. So can you trust this code? Are you sure it displayed correctly in all editors? If you did not write it or your language is not RTL, remove the special characters, as they could be used to trick you into executing code, that does something else than what it looks like. More Information: https://en.wikipedia.org/wiki/Bidirectional_text https://trojansource.codes/

invalid-character-backspace (E2510)
    Invalid unescaped character backspace, use "b" instead. Moves the cursor back, so the character after it will overwrite the character before.

invalid-character-carriage-return (E2511)
    Invalid unescaped character carriage-return, use "r" instead. Moves the cursor to the start of line, subsequent characters overwrite the start of the line.

invalid-character-esc (E2513)
    Invalid unescaped character esc, use "x1B" instead. Commonly initiates escape codes which allow arbitrary control of the terminal.

invalid-character-nul (E2514)
    Invalid unescaped character nul, use "0" instead. Mostly end of input for python.

invalid-character-sub (E2512)
    Invalid unescaped character sub, use "x1A" instead. Ctrl+Z "End of text" on Windows. Some programs (such as type) ignore the rest of the file after it.

invalid-character-zero-width-space (E2515)
    Invalid unescaped character zero-width-space, use "u200B" instead. Invisible space character could hide real code execution.

invalid-unicode-codec (E2501)
    UTF-16 and UTF-32 aren't backward compatible. Use UTF-8 instead For compatibility use UTF-8 instead of UTF-16/UTF-32. See also https://bugs.python.org/issue1503789 for a history of this issue. And https://softwareengineering.stackexchange.com/questions/102205/ for some possible problems when using UTF-16 for instance.

bad-file-encoding (C2503)
    PEP8 recommends UTF-8 as encoding for Python files PEP8 recommends UTF-8 default encoding for Python files. See https://peps.python.org/pep-0008/#source-file-encoding

  Unnecessary-Dunder-Call checker

Verbatim name of the checker is unnecessary-dunder-call.

  Unnecessary-Dunder-Call checker Messages

unnecessary-dunder-call (C2801)
    Unnecessarily calls dunder method %s. %s. Used when a dunder method is manually called instead of using the corresponding function/method/operator.

  Unnecessary Ellipsis checker

Verbatim name of the checker is unnecessary_ellipsis.

  Unnecessary Ellipsis checker Messages

unnecessary-ellipsis (W2301)
    Unnecessary ellipsis constant Used when the ellipsis constant is encountered and can be avoided. A line of code consisting of an ellipsis is unnecessary if there is a docstring on the preceding line or if there is a statement in the same scope.

  Unsupported Version checker

Verbatim name of the checker is unsupported_version.

  Unsupported Version checker Messages

using-f-string-in-unsupported-version (W2601)
    F-strings are not supported by all versions included in the py-version setting Used when the py-version set by the user is lower than 3.6 and pylint encounters a f-string.

using-final-decorator-in-unsupported-version (W2602)
    typing.final is not supported by all versions included in the py-version setting Used when the py-version set by the user is lower than 3.8 and pylint encounters a typing.final decorator.

  Variables checker

Verbatim name of the checker is variables.

See also variables checker's options' documentation

  Variables checker Messages

unpacking-non-sequence (E0633)
    Attempting to unpack a non-sequence%s Used when something which is not a sequence is used in an unpack assignment

invalid-all-format (E0605)
    Invalid format for __all__, must be tuple or list Used when __all__ has an invalid format.

potential-index-error (E0643)
    Invalid index for iterable length Emitted when an index used on an iterable goes beyond the length of that iterable.

invalid-all-object (E0604)
    Invalid object %r in __all__, must contain only strings Used when an invalid (non-string) object occurs in __all__.

no-name-in-module (E0611)
    No name %r in module %r Used when a name cannot be found in a module.

undefined-variable (E0602)
    Undefined variable %r Used when an undefined variable is accessed.

undefined-all-variable (E0603)
    Undefined variable name %r in __all__ Used when an undefined variable name is referenced in __all__.

used-before-assignment (E0601)
    Using variable %r before assignment Emitted when a local variable is accessed before its assignment took place. Assignments in try blocks are assumed not to have occurred when evaluating associated except/finally blocks. Assignments in except blocks are assumed not to have occurred when evaluating statements outside the block, except when the associated try block contains a return statement.

cell-var-from-loop (W0640)
    Cell variable %s defined in loop A variable used in a closure is defined in a loop. This will result in all closures using the same value for the closed-over variable.

global-variable-undefined (W0601)
    Global variable %r undefined at the module level Used when a variable is defined through the "global" statement but the variable is not defined in the module scope.

self-cls-assignment (W0642)
    Invalid assignment to %s in method Invalid assignment to self or cls in instance or class method respectively.

unbalanced-dict-unpacking (W0644)
    Possible unbalanced dict unpacking with %s: left side has %d label%s, right side has %d value%s Used when there is an unbalanced dict unpacking in assignment or for loop

unbalanced-tuple-unpacking (W0632)
    Possible unbalanced tuple unpacking with sequence %s: left side has %d label%s, right side has %d value%s Used when there is an unbalanced tuple unpacking in assignment

possibly-unused-variable (W0641)
    Possibly unused variable %r Used when a variable is defined but might not be used. The possibility comes from the fact that locals() might be used, which could consume or not the said variable

redefined-builtin (W0622)
    Redefining built-in %r Used when a variable or function override a built-in.

redefined-outer-name (W0621)
    Redefining name %r from outer scope (line %s) Used when a variable's name hides a name defined in an outer scope or except handler.

unused-import (W0611)
    Unused %s Used when an imported module or variable is not used.

unused-argument (W0613)
    Unused argument %r Used when a function or method argument is not used.

unused-wildcard-import (W0614)
    Unused import(s) %s from wildcard import of %s Used when an imported module or variable is not used from a 'from X import *' style import.

unused-variable (W0612)
    Unused variable %r Used when a variable is defined but not used.

global-variable-not-assigned (W0602)
    Using global for %r but no assignment is done When a variable defined in the global scope is modified in an inner scope, the 'global' keyword is required in the inner scope only if there is an assignment operation done in the inner scope.

undefined-loop-variable (W0631)
    Using possibly undefined loop variable %r Used when a loop variable (i.e. defined by a for loop or a list comprehension or a generator expression) is used outside the loop.

global-statement (W0603)
    Using the global statement Used when you use the "global" statement to update a global variable. Pylint discourages its usage. That doesn't mean you cannot use it!

global-at-module-level (W0604)
    Using the global statement at the module level Used when you use the "global" statement at the module level since it has no effect.

  Optional checkers

Pylint provides the following optional plugins:

•   Deprecated Builtins checker

•   Broad Try Clause checker

•   Else If Used checker

•   Code Style checker

•   Compare-To-Zero checker

•   Comparison-Placement checker

•   Confusing Elif checker

•   Consider Refactoring Into While checker

•   Consider Ternary Expression checker

•   Dict-Init-Mutate checker

•   Parameter Documentation checker

•   Docstyle checker

•   Dunder checker

•   Empty-Comment checker

•   Compare-To-Empty-String checker

•   Eq-Without-Hash checker

•   Consider-Using-Any-Or-All checker

•   Magic-Value checker

•   Design checker

•   No Self Use checker

•   Overlap-Except checker

•   Import-Private-Name checker

•   Redefined-Loop-Name checker

•   Multiple Types checker

•   Set Membership checker

•   Typing checker

•   While Used checker

    You can activate any or all of these extensions by adding a load-plugins line to the MAIN section of your .pylintrc, for example:

    load-plugins=pylint.extensions.docparams,pylint.extensions.docstyle

  Broad Try Clause checker

This checker is provided by pylint.extensions.broad_try_clause. Verbatim name of the checker is broad_try_clause.

See also broad_try_clause checker's options' documentation

  Broad Try Clause checker Messages

too-many-try-statements (W0717)
    Try clause contains too many statements.

  Code Style checker

This checker is provided by pylint.extensions.code_style. Verbatim name of the checker is code_style.

  Code Style checker Documentation

Checkers that can improve code consistency. As such they don't necessarily provide a performance benefit and are often times opinionated.

See also code_style checker's options' documentation

  Code Style checker Messages

consider-using-tuple (R6102)
    Consider using an in-place tuple instead of list Only for style consistency! Emitted where an in-place defined list can be replaced by a tuple. Due to optimizations by CPython, there is no performance benefit from it.

consider-using-namedtuple-or-dataclass (R6101)
    Consider using namedtuple or dataclass for dictionary values Emitted when dictionary values can be replaced by namedtuples or dataclass instances.

consider-using-assignment-expr (R6103)
    Use '%s' instead Emitted when an if assignment is directly followed by an if statement and both can be combined by using an assignment expression :=. Requires Python 3.8 and py-version >= 3.8.

consider-using-augmented-assign (R6104)
    Use '%s' to do an augmented assign directly Emitted when an assignment is referring to the object that it is assigning to. This can be changed to be an augmented assign. Disabled by default!

  Compare-To-Empty-String checker

This checker is provided by pylint.extensions.emptystring. Verbatim name of the checker is compare-to-empty-string.

  Compare-To-Empty-String checker Messages

compare-to-empty-string (C1901)
    "%s" can be simplified to "%s" as an empty string is falsey Used when Pylint detects comparison to an empty string constant.

  Compare-To-Zero checker

This checker is provided by pylint.extensions.comparetozero. Verbatim name of the checker is compare-to-zero.

  Compare-To-Zero checker Messages

compare-to-zero (C2001)
    "%s" can be simplified to "%s" as 0 is falsey Used when Pylint detects comparison to a 0 constant.

  Comparison-Placement checker

This checker is provided by pylint.extensions.comparison_placement. Verbatim name of the checker is comparison-placement.

  Comparison-Placement checker Messages

misplaced-comparison-constant (C2201)
    Comparison should be %s Used when the constant is placed on the left side of a comparison. It is usually clearer in intent to place it in the right hand side of the comparison.

  Confusing Elif checker

This checker is provided by pylint.extensions.confusing_elif. Verbatim name of the checker is confusing_elif.

  Confusing Elif checker Messages

confusing-consecutive-elif (R5601)
    Consecutive elif with differing indentation level, consider creating a function to separate the inner elif Used when an elif statement follows right after an indented block which itself ends with if or elif. It may not be ovious if the elif statement was willingly or mistakenly unindented. Extracting the indented if statement into a separate function might avoid confusion and prevent errors.

  Consider-Using-Any-Or-All checker

This checker is provided by pylint.extensions.for_any_all. Verbatim name of the checker is consider-using-any-or-all.

  Consider-Using-Any-Or-All checker Messages

consider-using-any-or-all (C0501)
    `for` loop could be `%s` A for loop that checks for a condition and return a bool can be replaced with any or all.

  Consider Refactoring Into While checker

This checker is provided by pylint.extensions.consider_refactoring_into_while_condition. Verbatim name of the checker is consider_refactoring_into_while.

  Consider Refactoring Into While checker Messages

consider-refactoring-into-while-condition (R3501)
    Consider using 'while %s' instead of 'while %s:' an 'if', and a 'break' Emitted when while True: loop is used and the first statement is a break condition. The if / break construct can be removed if the check is inverted and moved to the while statement.

  Consider Ternary Expression checker

This checker is provided by pylint.extensions.consider_ternary_expression. Verbatim name of the checker is consider_ternary_expression.

  Consider Ternary Expression checker Messages

consider-ternary-expression (W0160)
    Consider rewriting as a ternary expression Multiple assign statements spread across if/else blocks can be rewritten with a single assignment and ternary expression

  Deprecated Builtins checker

This checker is provided by pylint.extensions.bad_builtin. Verbatim name of the checker is deprecated_builtins.

  Deprecated Builtins checker Documentation

This used to be the bad-builtin core checker, but it was moved to an extension instead. It can be used for finding prohibited used builtins, such as map or filter, for which other alternatives exists.

If you want to control for what builtins the checker should warn about, you can use the bad-functions option:

$ pylint a.py --load-plugins=pylint.extensions.bad_builtin --bad-functions=apply,reduce
...

See also deprecated_builtins checker's options' documentation

  Deprecated Builtins checker Messages

bad-builtin (W0141)
    Used builtin function %s Used when a disallowed builtin function is used (see the bad-function option). Usual disallowed functions are the ones like map, or filter , where Python offers now some cleaner alternative like list comprehension.

  Design checker

This checker is provided by pylint.extensions.mccabe. Verbatim name of the checker is design.

  Design checker Documentation

You can now use this plugin for finding complexity issues in your code base.

Activate it through pylint --load-plugins=pylint.extensions.mccabe. It introduces a new warning, too-complex, which is emitted when a code block has a complexity higher than a preestablished value, which can be controlled through the max-complexity option, such as in this example:

$ cat a.py
def f10():
    """McCabe rating: 11"""
    myint = 2
    if myint == 5:
        return myint
    elif myint == 6:
        return myint
    elif myint == 7:
        return myint
    elif myint == 8:
        return myint
    elif myint == 9:
        return myint
    elif myint == 10:
        if myint == 8:
            while True:
                return True
        elif myint == 8:
            with myint:
                return 8
    else:
        if myint == 2:
            return myint
        return myint
    return myint
$ pylint a.py --load-plugins=pylint.extensions.mccabe
R:1: 'f10' is too complex. The McCabe rating is 11 (too-complex)
$ pylint a.py --load-plugins=pylint.extensions.mccabe --max-complexity=50
$

See also design checker's options' documentation

  Design checker Messages

too-complex (R1260)
    %s is too complex. The McCabe rating is %d Used when a method or function is too complex based on McCabe Complexity Cyclomatic

  Dict-Init-Mutate checker

This checker is provided by pylint.extensions.dict_init_mutate. Verbatim name of the checker is dict-init-mutate.

  Dict-Init-Mutate checker Messages

dict-init-mutate (C3401)
    Declare all known key/values when initializing the dictionary. Dictionaries can be initialized with a single statement using dictionary literal syntax.

  Docstyle checker

This checker is provided by pylint.extensions.docstyle. Verbatim name of the checker is docstyle.

  Docstyle checker Messages

bad-docstring-quotes (C0198)
    Bad docstring quotes in %s, expected """, given %s Used when a docstring does not have triple double quotes.

docstring-first-line-empty (C0199)
    First line empty in %s docstring Used when a blank line is found at the beginning of a docstring.

  Dunder checker

This checker is provided by pylint.extensions.dunder. Verbatim name of the checker is dunder.

See also dunder checker's options' documentation

  Dunder checker Messages

bad-dunder-name (W3201)
    Bad or misspelled dunder method name %s. Used when a dunder method is misspelled or defined with a name not within the predefined list of dunder names.

  Else If Used checker

This checker is provided by pylint.extensions.check_elif. Verbatim name of the checker is else_if_used.

  Else If Used checker Messages

else-if-used (R5501)
    Consider using "elif" instead of "else" then "if" to remove one indentation level Used when an else statement is immediately followed by an if statement and does not contain statements that would be unrelated to it.

  Empty-Comment checker

This checker is provided by pylint.extensions.empty_comment. Verbatim name of the checker is empty-comment.

  Empty-Comment checker Messages

empty-comment (R2044)
    Line with empty comment Used when a # symbol appears on a line not followed by an actual comment

  Eq-Without-Hash checker

This checker is provided by pylint.extensions.eq_without_hash. Verbatim name of the checker is eq-without-hash.

  Eq-Without-Hash checker Messages

eq-without-hash (W1641)
    Implementing __eq__ without also implementing __hash__ Used when a class implements __eq__ but not __hash__. Objects get None as their default __hash__ implementation if they also implement __eq__.

  Import-Private-Name checker

This checker is provided by pylint.extensions.private_import. Verbatim name of the checker is import-private-name.

  Import-Private-Name checker Messages

import-private-name (C2701)
    Imported private %s (%s) Used when a private module or object prefixed with _ is imported. PEP8 guidance on Naming Conventions states that public attributes with leading underscores should be considered private.

  Magic-Value checker

This checker is provided by pylint.extensions.magic_value. Verbatim name of the checker is magic-value.

See also magic-value checker's options' documentation

  Magic-Value checker Messages

magic-value-comparison (R2004)
    Consider using a named constant or an enum instead of '%s'. Using named constants instead of magic values helps improve readability and maintainability of your code, try to avoid them in comparisons.

  Multiple Types checker

This checker is provided by pylint.extensions.redefined_variable_type. Verbatim name of the checker is multiple_types.

  Multiple Types checker Messages

redefined-variable-type (R0204)
    Redefinition of %s type from %s to %s Used when the type of a variable changes inside a method or a function.

  No Self Use checker

This checker is provided by pylint.extensions.no_self_use. Verbatim name of the checker is no_self_use.

  No Self Use checker Messages

no-self-use (R6301)
    Method could be a function Used when a method doesn't use its bound instance, and so could be written as a function.

  Overlap-Except checker

This checker is provided by pylint.extensions.overlapping_exceptions. Verbatim name of the checker is overlap-except.

  Overlap-Except checker Messages

overlapping-except (W0714)
    Overlapping exceptions (%s) Used when exceptions in handler overlap or are identical

  Parameter Documentation checker

This checker is provided by pylint.extensions.docparams. Verbatim name of the checker is parameter_documentation.

  Parameter Documentation checker Documentation

If you document the parameters of your functions, methods and constructors and their types systematically in your code this optional component might be useful for you. Sphinx style, Google style, and Numpy style are supported. (For some examples, see https://pypi.org/project/sphinxcontrib-napoleon/ .)

You can activate this checker by adding the line:

load-plugins=pylint.extensions.docparams

to the MAIN section of your .pylintrc.

This checker verifies that all function, method, and constructor docstrings include documentation of the

•   parameters and their types

•   return value and its type

•   exceptions raised

    and can handle docstrings in

•   Sphinx style (param, type, return, rtype, raise / except):

    def function_foo(x, y, z):
        '''function foo ...
        :param x: bla x
        :type x: int
        :param y: bla y
        :type y: float
        :param int z: bla z
        :return: sum
        :rtype: float
        :raises OSError: bla
        '''
        return x + y + z

•   or the Google style (Args:, Returns:, Raises:):

    def function_foo(x, y, z):
        '''function foo ...
        Args:
            x (int): bla x
            y (float): bla y
            z (int): bla z
        Returns:
            float: sum
        Raises:
            OSError: bla
        '''
        return x + y + z

•   or the Numpy style (Parameters, Returns, Raises):

    def function_foo(x, y, z):
        '''function foo ...
        Parameters
        ----------
        x: int
            bla x
        y: float
            bla y
        z: int
            bla z
        Returns
        -------
        float
            sum
        Raises
        ------
        OSError
            bla
        '''
        return x + y + z

    You'll be notified of missing parameter documentation but also of naming inconsistencies between the signature and the documentation which often arise when parameters are renamed automatically in the code, but not in the documentation. Note: by default docstrings of private and magic methods are not checked. To change this behaviour (for example, to also check __init__) add no-docstring-rgx=^(?!__init__$)_ to the BASIC section of your .pylintrc.

    Constructor parameters can be documented in either the class docstring or the __init__ docstring, but not both:

    class ClassFoo(object):
        '''Sphinx style docstring foo
        :param float x: bla x
        :param y: bla y
        :type y: int
        '''
        def __init__(self, x, y):
            pass
    class ClassBar(object):
        def __init__(self, x, y):
            '''Google style docstring bar
            Args:
                x (float): bla x
                y (int): bla y
            '''
            pass

    In some cases, having to document all parameters is a nuisance, for instance if many of your functions or methods just follow a common interface. To remove this burden, the checker accepts missing parameter documentation if one of the following phrases is found in the docstring:

•   For the other parameters, see

•   For the parameters, see

    (with arbitrary whitespace between the words). Please add a link to the docstring defining the interface, e.g. a superclass method, after "see":

    def callback(x, y, z):
        '''Sphinx style docstring for callback ...
        :param x: bla x
        :type x: int
        For the other parameters, see
        :class:`MyFrameworkUsingAndDefiningCallback`
        '''
        return x + y + z
    def callback(x, y, z):
        '''Google style docstring for callback ...
        Args:
            x (int): bla x
        For the other parameters, see
        :class:`MyFrameworkUsingAndDefiningCallback`
        '''
        return x + y + z

    Naming inconsistencies in existing parameter and their type documentations are still detected.

    See also parameter_documentation checker's options' documentation

  Parameter Documentation checker Messages

differing-param-doc (W9017)
    "%s" differing in parameter documentation Please check parameter names in declarations.

differing-type-doc (W9018)
    "%s" differing in parameter type documentation Please check parameter names in type declarations.

multiple-constructor-doc (W9005)
    "%s" has constructor parameters documented in class and __init__ Please remove parameter declarations in the class or constructor.

missing-param-doc (W9015)
    "%s" missing in parameter documentation Please add parameter declarations for all parameters.

missing-type-doc (W9016)
    "%s" missing in parameter type documentation Please add parameter type declarations for all parameters.

missing-raises-doc (W9006)
    "%s" not documented as being raised Please document exceptions for all raised exception types.

useless-param-doc (W9019)
    "%s" useless ignored parameter documentation Please remove the ignored parameter documentation.

useless-type-doc (W9020)
    "%s" useless ignored parameter type documentation Please remove the ignored parameter type documentation.

missing-any-param-doc (W9021)
    Missing any documentation in "%s" Please add parameter and/or type documentation.

missing-return-doc (W9011)
    Missing return documentation Please add documentation about what this method returns.

missing-return-type-doc (W9012)
    Missing return type documentation Please document the type returned by this method.

missing-yield-doc (W9013)
    Missing yield documentation Please add documentation about what this generator yields.

missing-yield-type-doc (W9014)
    Missing yield type documentation Please document the type yielded by this method.

redundant-returns-doc (W9008)
    Redundant returns documentation Please remove the return/rtype documentation from this method.

redundant-yields-doc (W9010)
    Redundant yields documentation Please remove the yields documentation from this method.

  Redefined-Loop-Name checker

This checker is provided by pylint.extensions.redefined_loop_name. Verbatim name of the checker is redefined-loop-name.

  Redefined-Loop-Name checker Messages

redefined-loop-name (W2901)
    Redefining %r from loop (line %s) Used when a loop variable is overwritten in the loop body.

  Set Membership checker

This checker is provided by pylint.extensions.set_membership. Verbatim name of the checker is set_membership.

  Set Membership checker Messages

use-set-for-membership (R6201)
    Consider using set for membership test Membership tests are more efficient when performed on a lookup optimized datatype like sets.

  Typing checker

This checker is provided by pylint.extensions.typing. Verbatim name of the checker is typing.

  Typing checker Documentation

Find issue specifically related to type annotations.

See also typing checker's options' documentation

  Typing checker Messages

broken-noreturn (E6004)
    'NoReturn' inside compound types is broken in 3.7.0 / 3.7.1 typing.NoReturn inside compound types is broken in Python 3.7.0 and 3.7.1. If not dependent on runtime introspection, use string annotation instead. E.g. Callable[..., 'NoReturn']. https://bugs.python.org/issue34921

broken-collections-callable (E6005)
    'collections.abc.Callable' inside Optional and Union is broken in 3.9.0 / 3.9.1 (use 'typing.Callable' instead) collections.abc.Callable inside Optional and Union is broken in Python 3.9.0 and 3.9.1. Use typing.Callable for these cases instead. https://bugs.python.org/issue42965

deprecated-typing-alias (W6001)
    '%s' is deprecated, use '%s' instead Emitted when a deprecated typing alias is used.

consider-using-alias (R6002)
    '%s' will be deprecated with PY39, consider using '%s' instead%s Only emitted if 'runtime-typing=no' and a deprecated typing alias is used in a type annotation context in Python 3.7 or 3.8.

consider-alternative-union-syntax (R6003)
    Consider using alternative Union syntax instead of '%s'%s Emitted when 'typing.Union' or 'typing.Optional' is used instead of the alternative Union syntax 'int | None'.

redundant-typehint-argument (R6006)
    Type `%s` is used more than once in union type annotation. Remove redundant typehints. Duplicated type arguments will be skipped by mypy tool, therefore should be removed to avoid confusion.

  While Used checker

This checker is provided by pylint.extensions.while_used. Verbatim name of the checker is while_used.

  While Used checker Messages

while-used (W0149)
    Used `while` loop Unbounded while loops can often be rewritten as bounded for loops. Exceptions can be made for cases such as event loops, listeners, etc.

  API

You can call Pylint, epylint, symilar and pyreverse from another Python program thanks to their APIs:

from pylint import run_pylint, run_pyreverse, run_symilar
run_pylint("--disable=C", "myfile.py")
run_pyreverse(...)
run_symilar(...)

  Pylint

  As you would launch the command line

You can use the run_pylint function, which is the same function called by the command line (using sys.argv). You can supply arguments yourself:

from pylint import run_pylint
run_pylint(argv=["--disable=line-too-long", "myfile.py"])

  Recover the result in a stream

You can also use pylint.lint.Run directly if you want to do something that can't be done using only pylint's command line options. Here's the basic example:

from pylint.lint import Run
Run(argv=["--disable=line-too-long", "myfile.py"])

With Run it is possible to invoke pylint programmatically with a reporter initialized with a custom stream:

from io import StringIO
from pylint.lint import Run
from pylint.reporters.text import TextReporter
pylint_output = StringIO()  # Custom open stream
reporter = TextReporter(pylint_output)
Run(["test_file.py"], reporter=reporter, exit=False)
print(pylint_output.getvalue())  # Retrieve and print the text report

The reporter can accept any stream object as as parameter. In this example, the stream outputs to a file:

from pylint.lint import Run
from pylint.reporters.text import TextReporter
with open("report.out", "w") as f:
    reporter = TextReporter(f)
    Run(["test_file.py"], reporter=reporter, exit=False)

This would be useful to capture pylint output in an open stream which can be passed onto another program.

If your program expects that the files being linted might be edited between runs, you will need to clear pylint's inference cache:

from pylint.lint import pylinter
pylinter.MANAGER.clear_cache()

  epylint

To silently run epylint on a module_name.py module, and get its standard output and error:

from pylint import epylint as lint
(pylint_stdout, pylint_stderr) = lint.py_run('module_name.py', return_std=True)

It is also possible to include additional Pylint options in the first argument to py_run:

from pylint import epylint as lint
(pylint_stdout, pylint_stderr) = lint.py_run('module_name.py --disable C0114', return_std=True)

The options --msg-template="{path}:{line}: {category} ({msg_id}, {symbol}, {obj}) {msg}" and --reports=n are set implicitly inside the epylint module.

  How To Guides

  How to Write a Checker

You can find some simple examples in the distribution (custom.py , custom_raw.py and deprecation_checker.py).

There are three kinds of checkers:

•   Raw checkers, which analyse each module as a raw file stream.

•   Token checkers, which analyse a file using the list of tokens that represent the source code in the file.

•   AST checkers, which work on an AST representation of the module.

    The AST representation is provided by the astroid library. astroid adds additional information and methods over ast in the standard library, to make tree navigation and code introspection easier.

  Writing an AST Checker

Let's implement a checker to make sure that all return nodes in a function return a unique constant. Firstly we will need to fill in some required boilerplate:

import astroid
from astroid import nodes
from typing import TYPE_CHECKING, Optional
from pylint.checkers import BaseChecker
if TYPE_CHECKING:
    from pylint.lint import PyLinter
class UniqueReturnChecker(BaseChecker):
    name = "unique-returns"
    msgs = {
        "W0001": (
            "Returns a non-unique constant.",
            "non-unique-returns",
            "All constants returned in a function should be unique.",
        ),
    }
    options = (
        (
            "ignore-ints",
            {
                "default": False,
                "type": "yn",
                "metavar": "<y or n>",
                "help": "Allow returning non-unique integers",
            },
        ),
    )

So far we have defined the following required components of our checker:

•

A name. The name is used to generate a special configuration
    section for the checker, when options have been provided.

•

A message dictionary. Each checker is being used for finding problems
    in your code, the problems being displayed to the user through messages. The message dictionary should specify what messages the checker is going to emit. See Defining a Message for the details about defining a new message.

    We have also defined an optional component of the checker. The options list defines any user configurable options. It has the following format:

    options = (
        ("option-symbol", {"argparse-like-kwarg": "value"}),
    )

•   The option-symbol is a unique name for the option. This is used on the command line and in config files. The hyphen is replaced by an underscore when used in the checker, similarly to how you would use argparse.Namespace:

    if not self.linter.config.ignore_ints:
        ...

    Next we'll track when we enter and leave a function.

    def __init__(self, linter: Optional["PyLinter"] = None) -> None:
        super().__init__(linter)
        self._function_stack = []
    def visit_functiondef(self, node: nodes.FunctionDef) -> None:
        self._function_stack.append([])
    def leave_functiondef(self, node: nodes.FunctionDef) -> None:
        self._function_stack.pop()

    In the constructor we initialise a stack to keep a list of return nodes for each function. An AST checker is a visitor, and should implement visit_<lowered class name> or leave_<lowered class name> methods for the nodes it's interested in. In this case we have implemented visit_functiondef and leave_functiondef to add a new list of return nodes for this function, and to remove the list of return nodes when we leave the function.

    Finally we'll implement the check. We will define a visit_return function, which is called with an .astroid.nodes.Return node.

    We'll need to be able to figure out what attributes an .astroid.nodes.Return node has available. We can use astroid.extract_node for this:

    >>> node = astroid.extract_node("return 5")
    >>> node
    <Return l.1 at 0x7efe62196390>
    >>> help(node)
    >>> node.value
    <Const.int l.1 at 0x7efe62196ef0>

    We could also construct a more complete example:

    >>> node_a, node_b = astroid.extract_node("""
    ... def test():
    ...     if True:
    ...         return 5 #@
    ...     return 5 #@
    ... """)
    >>> node_a.value
    <Const.int l.4 at 0x7efe621a74e0>
    >>> node_a.value.value
    5
    >>> node_a.value.value == node_b.value.value
    True

    For astroid.extract_node, you can use #@ at the end of a line to choose which statements will be extracted into nodes.

    For more information on astroid.extract_node, see the astroid documentation.

    Now we know how to use the astroid node, we can implement our check.

    def visit_return(self, node: nodes.Return) -> None:
        if not isinstance(node.value, nodes.Const):
            return
        for other_return in self._function_stack[-1]:
            if node.value.value == other_return.value.value and not (
                self.linter.config.ignore_ints and node.value.pytype() == int
            ):
                self.add_message("non-unique-returns", node=node)
        self._function_stack[-1].append(node)

    Once we have established that the source code has failed our check, we use ~.BaseChecker.add_message to emit our failure message.

    Finally, we need to register the checker with pylint. Add the register function to the top level of the file.

    def register(linter: "PyLinter") -> None:
        """This required method auto registers the checker during initialization.
        :param linter: The linter to register the checker to.
        """
        linter.register_checker(UniqueReturnChecker(linter))

    We are now ready to debug and test our checker!

  Debugging a Checker

It is very simple to get to a point where we can use pdb. We'll need a small test case. Put the following into a Python file:

def test():
    if True:
        return 5
    return 5
def test2():
    if True:
        return 1
    return 5

After inserting pdb into our checker and installing it, we can run pylint with only our checker:

$ pylint --load-plugins=my_plugin --disable=all --enable=non-unique-returns test.py
(Pdb)

Now we can debug our checker!

NOTE: my_plugin refers to a module called my_plugin.py. The preferred way of making this plugin available to pylint is by installing it as a package. This can be done either from a packaging index like PyPI or by installing it from a local source such as with pip install.

Alternatively, the plugin module can be made available to pylint by putting this module's parent directory in your PYTHONPATH environment variable.

If your pylint config has an init-hook that modifies sys.path to include the module's parent directory, this will also work, but only if either:

•   the init-hook and the load-plugins list are both defined in a configuration file, or...

•   the init-hook is passed as a command-line argument and the load-plugins list is in the configuration file

    So, you cannot load a custom plugin by modifying sys.path if you supply the init-hook in a configuration file, but pass the module name in via --load-plugins on the command line. This is because pylint loads plugins specified on command line before loading any configuration from other sources.

  Defining a Message

Pylint message is defined using the following format:

msgs = {
    "E0401": ( # message id
     "Unable to import %s", # template of displayed message
     "import-error", # message symbol
     "Used when pylint has been unable to import a module.",  # Message description
     { # Additional parameters:
          # message control support for the old names of the messages:
         "old_names": [("F0401", "old-import-error")]
         "minversion": (3, 5), # No check under this version
         "maxversion": (3, 7), # No check above this version
     },
 ),

The message is then formatted using the args parameter from add_message i.e. in self.add_message("import-error", args=module_we_cant_import, node=importnode), the value in module_we_cant_import say patglib will be interpolled and the final result will be: Unable to import patglib

•   The message-id should be a 4-digit number, prefixed with a message category. There are multiple message categories, these being C, W, E, F, R, standing for Convention, Warning, Error, Fatal and Refactoring. The 4 digits should not conflict with existing checkers and the first 2 digits should consistent across the checker (except shared messages).

•   The displayed-message is used for displaying the message to the user, once it is emitted.

•   The message-symbol is an alias of the message id and it can be used wherever the message id can be used.

•   The message-help is used when calling pylint --help-msg.

    Optionally message can contain optional extra options:

•   The old_names option permits to change the message id or symbol of a message without breaking the message control used on the old messages by users. The option is specified as a list of tuples (message-id, old-message-symbol) e.g. {"old_names": [("F0401", "old-import-error")]}. The symbol / msgid association must be unique so if you're changing the message id the symbol also need to change and you can generally use the old- prefix for that.

•   The minversion or maxversion options specify minimum or maximum version of python relevant for this message. The option value is specified as tuple with major version number as first number and minor version number as second number e.g. {"minversion": (3, 5)}

•   The shared option enables sharing message between multiple checkers. As mentioned previously, normally the message cannot be shared between multiple checkers. To allow having message shared between multiple checkers, the shared option must be set to True.

  Parallelize a Checker

BaseChecker has two methods get_map_data and reduce_map_data that permit to parallelize the checks when used with the -j option. If a checker actually needs to reduce data it should define get_map_data as returning something different than None and let its reduce_map_data handle a list of the types returned by get_map_data.

An example can be seen by looking at pylint/checkers/similar.py.

  Testing a Checker

Pylint is very well suited to test driven development. You can implement the template of the checker, produce all of your test cases and check that they fail, implement the checker, then check that all of your test cases work.

Pylint provides a pylint.testutils.CheckerTestCase to make test cases very simple. We can use the example code that we used for debugging as our test cases.

import astroid
import my_plugin
import pylint.testutils
class TestUniqueReturnChecker(pylint.testutils.CheckerTestCase):
    CHECKER_CLASS = my_plugin.UniqueReturnChecker
    def test_finds_non_unique_ints(self):
        func_node, return_node_a, return_node_b = astroid.extract_node("""
        def test(): #@
            if True:
                return 5 #@
            return 5 #@
        """)
        self.checker.visit_functiondef(func_node)
        self.checker.visit_return(return_node_a)
        with self.assertAddsMessages(
            pylint.testutils.MessageTest(
                msg_id="non-unique-returns",
                node=return_node_b,
            ),
        ):
            self.checker.visit_return(return_node_b)
    def test_ignores_unique_ints(self):
        func_node, return_node_a, return_node_b = astroid.extract_node("""
        def test(): #@
            if True:
                return 1 #@
            return 5 #@
        """)
        with self.assertNoMessages():
            self.checker.visit_functiondef(func_node)
            self.checker.visit_return(return_node_a)
            self.checker.visit_return(return_node_b)

Once again we are using astroid.extract_node to construct our test cases. pylint.testutils.CheckerTestCase has created the linter and checker for us, we simply simulate a traversal of the AST tree using the nodes that we are interested in.

  How To Write a Pylint Plugin

Pylint provides support for writing two types of extensions. First, there is the concept of checkers, which can be used for finding problems in your code. Secondly, there is also the concept of transform plugin, which represents a way through which the inference and the capabilities of Pylint can be enhanced and tailored to a particular module, library of framework.

In general, a plugin is a module which should have a function register, which takes an instance of pylint.lint.PyLinter as input.

A plugin can optionally define a function, load_configuration, which takes an instance of pylint.lint.PyLinter as input. This function is called after Pylint loads configuration from configuration file and command line interface. This function should load additional plugin specific configuration to Pylint.

So a basic hello-world plugin can be implemented as:

# Inside hello_plugin.py
from typing import TYPE_CHECKING
import astroid
if TYPE_CHECKING:
    from pylint.lint import PyLinter
def register(linter: "PyLinter") -> None:
  """This required method auto registers the checker during initialization.
  :param linter: The linter to register the checker to.
  """
  print('Hello world')

We can run this plugin by placing this module in the PYTHONPATH and invoking pylint as:

$ pylint -E --load-plugins hello_plugin foo.py
Hello world

We can extend hello-world plugin to ignore some specific names using load_configuration function:

# Inside hello_plugin.py
from typing import TYPE_CHECKING
import astroid
if TYPE_CHECKING:
    from pylint.lint import PyLinter
def register(linter: "PyLinter") -> None:
  """This required method auto registers the checker during initialization.
  :param linter: The linter to register the checker to.
  """
  print('Hello world')
def load_configuration(linter):
  name_checker = get_checker(linter, NameChecker)
  # We consider as good names of variables Hello and World
  name_checker.config.good_names += ('Hello', 'World')
  # We ignore bin directory
  linter.config.black_list += ('bin',)

Depending if we need a transform plugin or a checker, this might not be enough. For the former, this is enough to declare the module as a plugin, but in the case of the latter, we need to register our checker with the linter object, by calling the following inside the register function:

linter.register_checker(OurChecker(linter))

For more information on writing a checker see How to Write a Checker.

  Transform plugins

  Why write a plugin?

Pylint is a static analysis tool and Python is a dynamically typed language. So there will be cases where Pylint cannot analyze files properly (this problem can happen in statically typed languages also if reflection or dynamic evaluation is used).

The plugins are a way to tell Pylint how to handle such cases, since only the user would know what needs to be done. They are usually operating on the AST level, by modifying or changing it in a way which can ease its understanding by Pylint.

  Example

Let us run Pylint on a module from the Python source: warnings.py and see what happens:

amitdev$ pylint -E Lib/warnings.py
E:297,36: Instance of 'WarningMessage' has no 'message' member (no-member)
E:298,36: Instance of 'WarningMessage' has no 'filename' member (no-member)
E:298,51: Instance of 'WarningMessage' has no 'lineno' member (no-member)
E:298,64: Instance of 'WarningMessage' has no 'line' member (no-member)

Did we catch a genuine error? Let's open the code and look at WarningMessage class:

class WarningMessage(object):
  """Holds the result of a single showwarning() call."""
  _WARNING_DETAILS = ("message", "category", "filename", "lineno", "file",
                      "line")
  def __init__(self, message, category, filename, lineno, file=None,
                  line=None):
    local_values = locals()
    for attr in self._WARNING_DETAILS:
      setattr(self, attr, local_values[attr])
    self._category_name = category.__name__ if category else None
  def __str__(self):
    ...

Ah, the fields (message, category etc) are not defined statically on the class. Instead they are added using setattr. Pylint would have a tough time figuring this out.

  Enter Plugin

We can write a transform plugin to tell Pylint how to analyze this properly.

One way to fix our example with a plugin would be to transform the WarningMessage class, by setting the attributes so that Pylint can see them. This can be done by registering a transform function. We can transform any node in the parsed AST like Module, Class, Function etc. In our case we need to transform a class. It can be done so:

from typing import TYPE_CHECKING
import astroid
if TYPE_CHECKING:
    from pylint.lint import PyLinter
def register(linter: "PyLinter") -> None:
  """This required method auto registers the checker during initialization.
  :param linter: The linter to register the checker to.
  """
  pass
def transform(cls):
  if cls.name == 'WarningMessage':
    import warnings
    for f in warnings.WarningMessage._WARNING_DETAILS:
      cls.locals[f] = [astroid.ClassDef(f, None)]
astroid.MANAGER.register_transform(astroid.ClassDef, transform)

Let's go through the plugin. First, we need to register a class transform, which is done via the register_transform function in MANAGER. It takes the node type and function as parameters. We need to change a class, so we use astroid.ClassDef. We also pass a transform function which does the actual transformation.

transform function is simple as well. If the class is WarningMessage then we add the attributes to its locals (we are not bothered about type of attributes, so setting them as class will do. But we could set them to any type we want). That's it.

Note: We don't need to do anything in the register function of the plugin since we are not modifying anything in the linter itself.

Lets run Pylint with this plugin and see:

amitdev$ pylint -E --load-plugins warning_plugin Lib/warnings.py
amitdev$

All the false positives associated with WarningMessage are now gone. This is just an example, any code transformation can be done by plugins.

See astroid/brain for real life examples of transform plugins.

  Technical Reference

  Startup and the Linter Class

The two main classes in pylint.lint are .pylint.lint.Run and .pylint.lint.PyLinter.

The .pylint.lint.Run object is responsible for starting up pylint. It does some basic checking of the given command line options to find the initial hook to run, find the config file to use, and find which plugins have been specified. It can then create the main .pylint.lint.PyLinter instance and initialise it with the config file and plugins that were discovered when preprocessing the command line options. Finally the .pylint.lint.Run object launches any child linters for parallel jobs, and starts the linting process.

The .pylint.lint.PyLinter is responsible for coordinating the linting process. It parses the configuration and provides it for the checkers and other plugins, it handles the messages emitted by the checkers, it handles the output reporting, and it launches the checkers.

  Checkers

All of the default pylint checkers exist in pylint.checkers. This is where most of pylint's brains exist. Most checkers are AST based and so use astroid. pylint.checkers.utils provides a large number of utility methods for dealing with astroid.

  Contributing to pylint

The contributor guide will help you if you want to contribute to pylint itself.

  Contributing

  Finding something to do

Want to contribute to pylint? There's a lot of things you can do. Here's a list of links you can check depending on what you want to do:

•   Asking a question on discord, or on github

•   Opening an issue

•   Making the documentation better

•   Making the error message better

•   Reproducing bugs and confirming that issues are valid

•   Investigating or debugging complicated issues

•   Designing or specifying a solution

•   Giving your opinion on ongoing discussion

•   Fixing bugs and crashes

•   Fixing false positives

•   Creating new features or fixing false negatives

•   Reviewing pull requests

    If you are a pylint maintainer there's also:

•   Triaging issues

•   Labeling issues that do not have an actionable label yet

•   Preparing the next patch release

•   Checking stale pull requests status

  Creating a pull request

Got a change for Pylint? Below are a few steps you should take to make sure your patch gets accepted:

•   You must use at least Python 3.8 for development of Pylint as it gives you access to the latest ast parser and some pre-commit hooks do not support python 3.7.

•   Install the dev dependencies, see Contributor installation.

•   Use our test suite and write new tests, see Testing pylint.

•   Document your change, if it is a non-trivial one:

•   A maintainer might label the issue skip-news if the change does not need to be in the changelog.

•   Otherwise, create a news fragment with towncrier create <IssueNumber>.<type> which will be included in the changelog. <type> can be one of the types defined in ./towncrier.toml. If necessary you can write details or offer examples on how the new change is supposed to work.

•   Generating the doc is done with tox -e docs

•   Send a pull request from GitHub (see About pull requests for more insight about this topic).

•   Write comprehensive commit messages and/or a good description of what the PR does. Relate your change to an issue in the tracker if such an issue exists (see Closing issues via commit messages of the GitHub documentation for more information on this)

•   Keep the change small, separate the consensual changes from the opinionated one.

•   Don't hesitate to open multiple PRs if the change requires it. If your review is so big it requires to actually plan and allocate time to review, it's more likely that it's going to go stale.

•   Maintainers might have multiple 5 to 10 minutes review windows per day, Say while waiting for their teapot to boil, or for their partner to recover from their hilarious nerdy joke, but only one full hour review time per week, if at all.

•   If you used multiple emails or multiple names when contributing, add your mails and preferred name in the script/.contributors_aliases.json file.

  Tips for Getting Started with Pylint Development

•   Read the Technical Reference. It gives a short walk through of the pylint codebase and will help you identify where you will need to make changes for what you are trying to implement.

•   astroid.extract_node is your friend. Most checkers are AST based, so you will likely need to interact with astroid. A short example of how to use astroid.extract_node is given here.

•   When fixing a bug for a specific check, search the code for the warning message to find where the warning is raised, and therefore where the logic for that code exists.

•   When adding a new checker class you can use the get_unused_message_id_category.py script in ./script to get a message id that is not used by any of the other checkers.

  Building the documentation

You can use the makefile in the doc directory with make html to build the documentation. To test smaller changes you can consider build-html, which skips some checks but will be faster:

$ cd doc
$ make install-dependencies
$ make build-html

We're reusing generated files for speed, use make clean when you want to start from scratch.

  How to choose the target version ?

Choose depending on the kind of change you're doing:

•   In patch release (1.2.3), we only fix false positives and crashes.

•   In minor releases (1.2.0), we add checks, remove checks, drop python interpreters past end of life, upgrade astroid minor/major versions and fix false negatives.

•   In major releases (1.0.0) we change everything else (pylint options, json output, dev API...) while still trying to minimize disruption.

  Testing pylint

Pylint is very well tested and has a high code coverage. New contributions are not accepted unless they include tests.

  Contributor installation

  Basic installation

Pylint is developed using the git distributed version control system.

You can clone Pylint using

git clone https://github.com/PyCQA/pylint

Before you start testing your code, you need to install your source-code package locally. Suppose you just cloned pylint with the previous git clone command. To set up your environment for testing, open a terminal and run:

cd pylint
python3 -m venv venv
source venv/bin/activate
pip install -r requirements_test_min.txt

This ensures your testing environment is similar to Pylint's testing environment on GitHub.

Optionally (Because there's an auto-fix if you open a merge request): We have pre-commit hooks which should take care of the autoformatting for you before each commit. To enable it, run pre-commit install in the pylint root directory.

  Astroid installation

If you're testing new changes in astroid you need to also clone astroid and install with an editable installation alongside pylint as follows:

# Suppose you're in the pylint directory
git clone https://github.com/PyCQA/astroid.git
python3 -m pip install -e astroid/

You're now using the local astroid in pylint and can control the version with git for example:

cd astroid/
git switch my-astroid-dev-branch

  Launching tests

  pytest

Since we use pytest to run the tests, you can also use it on its own. We do recommend using the tox command though:

pytest pylint -k test_functional

You can use pytest directly. If you want to run tests on a specific portion of the code with pytest and your local python version:

python3 -m pytest

Everything in tests/message with coverage for the relevant code (require pytest-cov):

python3 -m pytest tests/message/ --cov=pylint.message
coverage html

Only the functional test "missing_kwoa_py3":

python3 -m pytest "tests/test_functional.py::test_functional[missing_kwoa_py3]"

  tox

You can also optionally install tox and run our tests using the tox package, as in:

python -m tox
python -m tox -epy38 # for Python 3.8 suite only
python -m tox -epylint # for running Pylint over Pylint's codebase
python -m tox -eformatting # for running formatting checks over Pylint's codebase

It's usually a good idea to run tox with --recreate. This flag tells tox to re-download all dependencies before running the tests. This can be important when a new version of astroid or any of the other dependencies has been published:

python -m tox --recreate # The entire tox environment will be recreated
python -m tox --recreate -e py310 # The python 3.10 tox environment will be recreated

To run only a specific test suite, use a pattern for the test filename (without the .py extension), as in:

python -m tox -e py310 -- -k test_functional
python -m tox -e py310 -- -k  \*func\*
python -m tox --recreate -e py310 -- -k test_functional # With recreation of the environment

  Primer tests

Pylint also uses what we refer to as primer tests. These are tests that are run automatically in our Continuous Integration and check whether any changes in Pylint lead to crashes or fatal errors on the stdlib, and also assess a pull request's impact on the linting of a selection of external repositories by posting the diff against pylint's current output as a comment.

To run the primer test for the stdlib, which only checks for crashes and fatal errors, you can add --primer-stdlib to the pytest command. For example:

pytest -m primer_stdlib --primer-stdlib

To produce the output generated on Continuous Integration for the linting of external repositories, run these commands:

python tests/primer/__main__.py prepare --clone
python tests/primer/__main__.py run --type=pr

To fully simulate the process on Continuous Integration, you should then checkout main, and then run these commands:

python tests/primer/__main__.py run --type=main
python tests/primer/__main__.py compare

The list of repositories is created on the basis of three criteria: 1) projects need to use a diverse range of language features, 2) projects need to be well maintained and 3) projects should not have a codebase that is too repetitive. This guarantees a good balance between speed of our CI and finding potential bugs.

You can find the latest list of repositories and any relevant code for these tests in the tests/primer directory.

  Writing tests

Pylint uses three types of tests: unittests, functional tests and primer tests.

•   unittests can be found in pylint/tests. Unless you're working on pylint's internal you're probably not going to have to write any.

•   Global functional tests can be found in the pylint/tests/functional. They are mainly used to test whether Pylint emits the correct messages.

•   Configuration's functional tests can be found in the pylint/tests/config/functional. They are used to test Pylint's configuration loading.

•   Primer tests you can suggest a new external repository to check but there's nothing to do most of the time.

  Unittest tests

Most other tests reside in the '/pylint/test' directory. These unittests can be used to test almost all functionality within Pylint. A good step before writing any new unittests is to look at some tests that test a similar funcitionality. This can often help write new tests.

If your new test requires any additional files you can put those in the /pylint/test/regrtest_data directory. This is the directory we use to store any data needed for the unittests.

  Functional tests

These are located under /pylint/test/functional and they are formed of multiple components. First, each Python file is considered to be a test case and it should be accompanied by a .txt file, having the same name. The .txt file contains the pylint messages that are supposed to be emitted by the given test file.

In your .py test file, each line for which Pylint is supposed to emit a message has to be annotated with a comment following this pattern # [message_symbol], as in:

a, b, c = 1 # [unbalanced-tuple-unpacking]

If multiple messages are expected on the same line, then this syntax can be used:

a, b, c = 1.test # [unbalanced-tuple-unpacking, no-member]

You can also use # +n: [ where n is an integer to deal with special cases, e.g., where the above regular syntax makes the line too long:

A = 5
# +1: [singleton-comparison]
B = A == None  # The test will look for the `singleton-comparison` message in this line

If you need special control over Pylint's configuration, you can also create a .rc file, which can set sections of Pylint's configuration. The .rc file can also contain a section [testoptions] to pass options for the functional test runner. The following options are currently supported:

•   "min_pyver": Minimal python version required to run the test

•   "max_pyver": Python version from which the test won't be run. If the last supported version is 3.9 this setting should be set to 3.10.

•   "min_pyver_end_position": Minimal python version required to check the end_line and end_column attributes of the message

•   "requires": Packages required to be installed locally to run the test

•   "except_implementations": List of python implementations on which the test should not run

•   "exclude_platforms": List of operating systems on which the test should not run

    Functional test file locations

    For existing checkers, new test cases should preferably be appended to the existing test file. For new checkers, a new file new_checker_message.py should be created (Note the use of underscores). This file should then be placed in the test/functional/n sub-directory.

    Some additional notes:

•   If the checker is part of an extension the test should go in test/functional/ext/extension_name

•   If the test is a regression test it should go in test/r/regression or test/r/regression_02. The file name should start with regression_.

•   For some sub-directories, such as test/functional/u, there are additional sub-directories (test/functional/u/use). Please check if your test file should be placed in any of these directories. It should be placed there if the sub-directory name matches the word before the first underscore of your test file name.

    The folder structure is enforced when running the test suite, so you might be directed to put the file in a different sub-directory.

    Running and updating functional tests

    During development, it's sometimes helpful to run all functional tests in your current environment in order to have faster feedback. Run from Pylint root directory with:

    python tests/test_functional.py

    You can use all the options you would use for pytest, for example -k "test_functional[len_checks]". Furthermore, if required the .txt file with expected messages can be regenerated based on the the current output by appending --update-functional-output to the command line:

    python tests/test_functional.py --update-functional-output -k "test_functional[len_checks]"

  Functional tests for configurations

To test the different ways to configure Pylint there is also a small functional test framework for configuration files. These tests can be found in the '/pylint/test/config' directory.

To create a new test create a new file with an unused name in the directory of that type of configuration file. Subsequently add a filename.result.json file with 'filename' being the same name as your configuration file. This file should record what the configuration should be compared to the standard configuration.

For example, if the configuration should add a warning to the list of disabled messages and you changed the configuration for job to 10 instead of the default 1 the .json file should include:

"functional_append": {
    "disable": [["a-message-to-be-added"],]
}
"jobs": 10,

Similarly if a message should be removed you can add the following to the .json file:

"functional_remove": {
    "disable": [["a-message-to-be-removed"],]
}

If a configuration is incorrect and should lead to a crash or warning being emitted you can specify this by adding a .out file. This file should have the following name name_of_configuration_testfile.error_code.out. So, if your test is called bad_configuration.toml and should exit with exit code 2 the .out file should be named bad_configuration.2.out. The content of the .out file should have a similar pattern as a normal Pylint output. Note that the module name should be {abspath} and the file name {relpath}.

  Profiling and performance analysis

  Performance analysis for Pylint

To analyse the performance of Pylint we recommend to use the cProfile module from stdlib. Together with the pstats module this should give you all the tools you need to profile a Pylint run and see which functions take how long to run.

The documentation for both modules can be found at cProfile.

To profile a run of Pylint over itself you can use the following code and run it from the base directory. Note that cProfile will create a document called stats that is then read by pstats. The human-readable output will be stored by pstats in ./profiler_stats. It will be sorted by cumulative time:

import cProfile
import pstats
import sys
sys.argv = ["pylint", "pylint"]
cProfile.run("from pylint import __main__", "stats")
with open("profiler_stats", "w", encoding="utf-8") as file:
    stats = pstats.Stats("stats", stream=file)
    stats.sort_stats("cumtime")
    stats.print_stats()

You can also interact with the stats object by sorting or restricting the output. For example, to only print functions from the pylint module and sort by cumulative time you could use:

import cProfile
import pstats
import sys
sys.argv = ["pylint", "pylint"]
cProfile.run("from pylint import __main__", "stats")
with open("profiler_stats", "w", encoding="utf-8") as file:
    stats = pstats.Stats("stats", stream=file)
    stats.sort_stats("cumtime")
    stats.print_stats("pylint/pylint")

Lastly, to profile a run over your own module or code you can use:

import cProfile
import pstats
import sys
sys.argv = ["pylint", "your_dir/your_file"]
cProfile.run("from pylint import __main__", "stats")
with open("profiler_stats", "w", encoding="utf-8") as file:
    stats = pstats.Stats("stats", stream=file)
    stats.sort_stats("cumtime")
    stats.print_stats()

The documentation of the pstats module discusses other possibilities to interact with the profiling output.

  Performance analysis of a specific checker

To analyse the performance of specific checker within Pylint we can use the human-readable output created by pstats.

If you search in the profiler_stats file for the file name of the checker you will find all functional calls from functions within the checker. Let's say we want to check the visit_importfrom method of the variables checker:

ncalls  tottime  percall  cumtime  percall filename:lineno(function)
622    0.006    0.000    8.039    0.013 /MY_PROGRAMMING_DIR/pylint/pylint/checkers/variables.py:1445(visit_importfrom)

The previous line tells us that this method was called 622 times during the profile and we were inside the function itself for 6 ms in total. The time per call is less than a millisecond (0.006 / 622) and thus is displayed as being 0.

Often you are more interested in the cumulative time (per call). This refers to the time spent within the function and any of the functions it called or the functions they called (etc.). In our example, the visit_importfrom method and all of its child-functions took a little over 8 seconds to exectute, with an execution time of 0.013 ms per call.

You can also search the profiler_stats for an individual function you want to check. For example _analyse_fallback_blocks, a function called by visit_importfrom in the variables checker. This allows more detailed analysis of specific functions:

ncalls  tottime  percall  cumtime  percall filename:lineno(function)
1    0.000    0.000    0.000    0.000 /MY_PROGRAMMING_DIR/pylint/pylint/checkers/variables.py:1511(_analyse_fallback_blocks)

  Parsing the profiler stats with other tools

Often you might want to create a visual representation of your profiling stats. A good tool to do this is gprof2dot. This tool can create a .dot file from the profiling stats created by cProfile and pstats. You can then convert the .dot file to a .png file with one of the many converters found online.

You can read the gprof2dot documentation for installation instructions for your specific environment.

Another option would be snakeviz.

  Releasing a pylint version

So, you want to release the X.Y.Z version of pylint ?

  Releasing a major or minor version

Before releasing a major or minor version check if there are any unreleased commits on the maintenance branch. If so, release a last patch release first. See Releasing a patch version.

•   Write the Summary -- Release highlights in doc/whatsnew and upgrade the release date.

•   Install the release dependencies: pip3 install -r requirements_test.txt

•   Bump the version and release by using tbump X.Y.0 --no-push --no-tag. (For example: tbump 2.4.0 --no-push --no-tag)

•   Check the commit created with git show amend the commit if required.

•   Create a new What's new in Pylint X.Y+1 document. Add it to doc/index.rst. Take a look at the examples from doc/whatsnew. Commit that with git commit -am "wip".

•   Move the main branch up to a dev version with tbump:

    tbump X.Y+1.0-dev0 --no-tag --no-push  # You can interrupt after the first step
    git commit -am "Upgrade the version to x.y+1.0-dev0 following x.y.0 release"

    For example:

    tbump 2.5.0-dev0 --no-tag --no-push
    git commit -am "Upgrade the version to 2.5.0-dev0 following 2.4.0 release"

    Check the commit, fixup the 'wip' commit with the what's new then push to a release branch

•   Open a merge request with the two commits (no one can push directly on main)

•   After the merge, recover the merged commits on main and tag the first one (the version should be X.Y.Z) as vX.Y.Z (For example: v2.4.0)

•   Push the tag.

•   Release the version on GitHub with the same name as the tag and copy and paste the appropriate changelog in the description. This triggers the PyPI release.

•   Delete the maintenance/X.Y-1.x branch. (For example: maintenance/2.3.x)

•   Create a maintenance/X.Y.x (For example: maintenance/2.4.x from the v2.4.0 tag.)

•   Close the current milestone and create the new ones (For example: close 2.4.0, create 2.4.1 and 2.6.0)

•   Hide and deactivate all the patch releases for the previous minor release on readthedoc, except the last one. (For example: hide v2.4.0, v2.4.1, v2.4.2 and keep only v2.4.3)

  Back-porting a fix from main to the maintenance branch

Whenever a PR on main should be released in a patch release on the current maintenance branch:

•   Label the PR with backport maintenance/X.Y-1.x. (For example backport maintenance/2.3.x)

•   Squash the PR before merging (alternatively rebase if there's a single commit)

•   (If the automated cherry-pick has conflicts)

•   Add a Needs backport label and do it manually.

•   You might alternatively also:

•   Cherry-pick the changes that create the conflict if it's not a new feature before doing the original PR cherry-pick manually.

•   Decide to wait for the next minor to release the PR

•   In any case upgrade the milestones in the original PR and newly cherry-picked PR to match reality.

•   Release a patch version

  Releasing a patch version

We release patch versions when a crash or a bug is fixed on the main branch and has been cherry-picked on the maintenance branch.

•   Install the release dependencies: pip3 install -r requirements_test.txt

•   Bump the version and release by using tbump X.Y-1.Z --no-push. (For example: tbump 2.3.5 --no-push)

•   Check the result visually with git show.

•   Open a merge request of release-X.Y-1.Z' in maintenance/X.Y.x (For example: release-2.3.5-branch in maintenance/2.3.x) to run the CI tests for this branch.

•   Create and push the tag.

•   Release the version on GitHub with the same name as the tag and copy and paste the changelog from the ReadtheDoc generated documentation from the pull request pipeline in the description. This triggers the PyPI release.

•   Merge the maintenance/X.Y.x branch on the main branch. The main branch should have the changelog for X.Y-1.Z+1 (For example v2.3.6). This merge is required so pre-commit autoupdate works for pylint.

•   Fix version conflicts properly, or bump the version to X.Y.0-devZ (For example: 2.4.0-dev6) before pushing on the main branch

•   Close the current milestone and create the new one (For example: close 2.3.5, create 2.3.6)

  Milestone handling

We move issues that were not done to the next milestone and block releases only if there are any open issues labelled as blocker.

  Governance

  How to become part of the project ?

  How to become a contributor ?

•   Follow the code of conduct

•   Search by yourself before asking for help

•   Open an issue

•   Investigate an issue and report your finding

•   Open a merge request directly if you feel it's a consensual change

    Reporting a bug is being a contributor already.

  How to become a triager ?

•   Contribute for more than 3 releases consistently.

•   Do not be too opinionated, follow the code of conduct without requiring emotional works from the maintainers. It does not mean that disagreements are impossible, only that arguments should stay technical and reasonable so the conversation is civil and productive.

•   Have a maintainer suggest that you become triager, without you asking

•   Get unanimous approval or neutral agreement from current maintainers.

  How to become a maintainer ?

•   Contribute two big code merge requests over multiple releases (for example one checker in 2.13 and the following bug after release and one complicated bug fixes in 2.14). Otherwise contributing for more than 3 releases consistently with great technical and interpersonal skills.

•   Take ownership of a part of the code that is not maintained well at the moment or that you contributed personally (if we feel we can't merge something without your review, you're going to be able to merge those yourself soon).

•   Triage for multiple months (close duplicate, clean up issues, answer questions...)

•   Have an admin suggest that you become maintainer, without you asking

•   Get unanimous approval or neutral agreement from current maintainers.

  How to become an admin ?

•   Contribute for several hundreds of commits over a long period of time with excellent interpersonal skills and code quality.

•   Maintain pylint for multiple years (code review, triaging and maintenance tasks).

•   At this point probably have another admin leave the project or become inactive for years.

•   Have an admin suggest that you become an admin, without you asking.

•   Get unanimous approval or neutral agreement from current admins.

  How are decisions made ?

Everyone is expected to follow the code of conduct. pylint is a do-ocracy / democracy. You're not allowed to behave poorly because you contributed a lot. But if you're not going to do the future maintenance work, your valid opinions might not be taken into account by those that will be affected by it.

  What are the fundamental tenets of pylint development?

General:

•   We favor correctness over performance, because pylint is not used primarily for its performance. Performance is still important and needs to be taken into account from the get go.

•   We then favor false negatives over false positives if correctness is impossible to achieve.

•   We try to keep the configuration sane, but if there's a hard decision to take we add an option so that pylint is multiple sizes fit all (after configuration)

    Where to add a new checker or message:

•   Error messages (things that will result in an error if run) should be builtin checks, activated by default

•   Messages that are opinionated, even slightly, should be opt-in (added as an extension)

•   We don't shy away from opinionated checks (like the while checker), but there's such a thing as too opinionated, if something is too opinionated it should be an external pylint plugin.

  How are disagreements handled ?

When something is not consensual users, maintainers, and admins discuss until an agreement is reached.

Depending on the difficulty of the discussion and the importance of a fast resolution, a decision can be taken:

•   Unanimously between discussion participants, contributors and maintainers (preferably)

•   By asking discussion participants for their opinions with an emoji survey in the issue and then using the majority if no maintainers feel strongly about the issue.

•   By majority of admins if no admins feel strongly about the issue.

•   By asking all users for their opinions in a new issue that will be pinned for multiple months before taking the decision if two admins feel strongly on an opposite side of the issue. Once the result is obvious the majority decision is not up for discussion anymore.

  Pyreverse

pyreverse analyzes your source code and generates package and class diagrams.

It supports output to .dot/.gv, .vcg, .puml/.plantuml (PlantUML) and .mmd/.html (MermaidJS) file formats. If Graphviz (or the dot command) is installed, all output formats supported by Graphviz can be used as well. In this case, pyreverse first generates a temporary .gv file, which is then fed to Graphviz to generate the final image.

  Running Pyreverse

To run pyreverse, use:

pyreverse [options] <packages>

<packages> can also be a single Python module. To see a full list of the available options, run:

pyreverse -h

  Example Output

Example diagrams generated with the .puml output format are shown below.

  Class Diagram
[image: Class diagram generated by pyreverse] [image]

  Package Diagram
[image: Package diagram generated by pyreverse] [image]

  Creating Class Diagrams for Specific Classes

In many cases creating a single diagram depicting all classes in the project yields a rather unwieldy, giant diagram. While limiting the input path to a single package or module can already help greatly to narrow down the scope, the -c option provides another way to create a class diagram focusing on a single class and its collaborators. For example, running:

pyreverse -ASmy -c pylint.checkers.classes.ClassChecker pylint

will generate the full class and package diagrams for pylint, but will additionally generate a file pylint.checkers.classes.ClassChecker.dot: [image: Package diagram generated by pyreverse] [image]

  Symilar

The console script symilar finds copy pasted blocks in a set of files. It provides a command line interface to the Similar class, which includes the logic for Pylint's duplicate-code message. It can be invoked with:

symilar [-d|--duplicates min_duplicated_lines] [-i|--ignore-comments] [--ignore-docstrings] [--ignore-imports] [--ignore-signatures] file1...

All files that shall be checked have to be passed in explicitly, e.g.:

symilar foo.py, bar.py, subpackage/spam.py, subpackage/eggs.py

symilar produces output like the following:

17 similar lines in 2 files
==tests/data/clientmodule_test.py:3
==tests/data/suppliermodule_test.py:12
  class Ancestor:
      """ Ancestor method """
      __implements__ = (Interface,)
      cls_member = DoNothing()
      def __init__(self, value):
          local_variable = 0
          self.attr = 'this method shouldn\'t have a docstring'
          self.__value = value
      def get_value(self):
          """ nice docstring ;-) """
          return self.__value
      def set_value(self, value):
          self.__value = value
          return 'this method shouldn\'t have a docstring'
TOTAL lines=58 duplicates=17 percent=29.31

  2.x

From pylint's beginning to pylint 2.14.0 included, we had a changelog that contained all nontrivial changes to Pylint, including changes that were not user facing, i.e. change that might interest you only if you're a developer working on pylint or pylint plugins or an open-source historian.

From pylint 1.6.0 to 2.14.0, on top of the full changelog there was also a summary of (mostly user facing) changes.

  What's New in Pylint 2.17

Release
    2.17

Date
    2023-03-08

  Summary -- Release highlights

2.17 is a small release that is the first to support python 3.11 officially with the addition of TryStar nodes.

There's still two new default checks: bad-chained-comparison and implicit-flag-alias, one of them already fixed a previously undetected bug in sentry.

Thanks to the community effort our documentation is almost complete, and every messages should have a proper documentation now. A big thank you to everyone who participated !

The next release is going to be 3.0.0, bring breaking changes and enact long announced deprecations. There's going to be frequent beta releases, before the official releases, everyone is welcome to try the betas so we find problems before the actual release.

  What's new in Pylint 2.17.2?

Release date: 2023-04-03

  False Positives Fixed

•   invalid-name now allows for integers in typealias names: - now valid: Good2Name, GoodName2. - still invalid: _1BadName.

    Closes #8485 (#8485)

•   No longer consider Union as type annotation as type alias for naming checks.

    Closes #8487 (#8487)

•   unnecessary-lambda no longer warns on lambdas which use its parameters in their body (other than the final arguments), e.g. lambda foo: (bar if foo else baz)(foo).

    Closes #8496 (#8496)

  Other Bug Fixes

•   Fix a crash in pyreverse when "/" characters are used in the output filename e.g pyreverse -o png -p name/ path/to/project.

    Closes #8504 (#8504)

  What's new in Pylint 2.17.1?

Release date: 2023-03-22

  False Positives Fixed

•   Adds asyncSetUp to the default defining-attr-methods list to silence attribute-defined-outside-init warning when using unittest.IsolatedAsyncioTestCase.

    Refs #8403 (#8403)

  Other Bug Fixes

•   --clear-cache-post-run now also clears LRU caches for pylint utilities holding references to AST nodes.

    Closes #8361 (#8361)

•   Fix a crash when TYPE_CHECKING is used without importing it.

    Closes #8434 (#8434)

•   Fix a regression of preferred-modules where a partial match was used instead of the required full match.

    Closes #8453 (#8453)

  Internal Changes

•   The following utilities are deprecated in favor of the more robust in_type_checking_block and will be removed in pylint 3.0:

•   is_node_in_guarded_import_block

•   is_node_in_typing_guarded_import_block

•   is_typing_guard

    is_sys_guard is still available, which was part of is_node_in_guarded_import_block.

    Refs #8433 (#8433)

  What's new in Pylint 2.17.0?

Release date: 2023-03-08

  New Features

•   pyreverse now supports custom color palettes with the --color-palette option.

    Closes #6738 (#6738)

•   Add invalid-name check for TypeAlias names.

    Closes #7081. (#7081)

•   Accept values of the form <class name>.<attribute name> for the exclude-protected list.

    Closes #7343 (#7343)

•   Add --version option to pyreverse.

    Refs #7851 (#7851)

•   Adds new functionality with preferred-modules configuration to detect submodules.

    Refs #7957 (#7957)

•   Support implicit namespace packages (PEP 420).

    Closes #8154 (#8154)

•   Add globbing pattern support for --source-roots.

    Closes #8290 (#8290)

•   Support globbing pattern when defining which file/directory/module to lint.

    Closes #8310 (#8310)

•   pylint now supports TryStar nodes from Python 3.11 and should be fully compatible with Python 3.11.

    Closes #8387 (#8387)

  New Checks

•   Add a bad-chained-comparison check that emits a warning when there is a chained comparison where one expression is semantically incompatible with the other.

    Closes #6559 (#6559)

•   Adds an implicit-flag-alias check that emits a warning when a class derived from enum.IntFlag assigns distinct integer values that share common bit positions.

    Refs #8102 (#8102)

  False Positives Fixed

•   Fix various false positives for functions that return directly from structural pattern matching cases.

    Closes #5288 (#5288)

•   Fix false positive for used-before-assignment when typing.TYPE_CHECKING is used with if/elif/else blocks.

    Closes #7574 (#7574)

•   Fix false positive for isinstance-second-argument-not-valid-type with union types.

    Closes #8205 (#8205)

•   Fix false positive for used-before-assignment for named expressions appearing after the first element in a list, tuple, or set.

    Closes #8252 (#8252)

•   Fix false positive for wrong-spelling-in-comment with class names in a python 2 type comment.

    Closes #8370 (#8370)

  False Negatives Fixed

•   Fix a false negative for 'missing-parentheses-for-call-in-test' when inference failed for the internal of the call as we did not need that information to raise correctly.

    Refs #8185 (#8185)

•   Fix false negative for inconsistent-returns with while-loops.

    Closes #8280 (#8280)

  Other Bug Fixes

•   Fix used-before-assignment false positive when the walrus operator is used with a ternary operator in dictionary key/value initialization.

    Closes #8125 (#8125)

•   Fix no-name-in-module false positive raised when a package defines a variable with the same name as one of its submodules.

    Closes #8148 (#8148)

•   Fix a crash happening for python interpreter < 3.9 following a failed typing update.

    Closes #8161 (#8161)

•   Fix nested-min-max suggestion message to indicate it's possible to splat iterable objects.

    Closes #8168 (#8168)

•   Fix a crash happening when a class attribute was negated in the start argument of an enumerate.

    Closes #8207 (#8207)

•   Prevent emitting invalid-name for the line on which a global statement is declared.

    Closes #8307 (#8307)

  Other Changes

•   Update explanation for global-variable-not-assigned and add confidence.

    Closes #5073 (#5073)

•   The governance model and the path to become a maintainer have been documented as part of our effort to guarantee that the software supply chain in which pylint is included is secure.

    Refs #8329 (#8329)

  What's New in Pylint 2.16

Release
    2.16

Date
    2023-02-01

  Summary -- Release highlights

In 2.16.0 we added aggregation and composition understanding in pyreverse, and a way to clear the cache in between run in server mode (originally for the VS Code integration). Apart from the bug fixes there's also a lot of new checks, and new extensions that have been asked for for a long time that were implemented.

If you want to benefit from all the new checks load the following plugins:

pylint.extensions.dict_init_mutate,
pylint.extensions.dunder,
pylint.extensions.typing,
pylint.extensions.magic_value,

We still welcome any community effort to help review, integrate, and add good/bad examples to the doc for <https://github.com/PyCQA/pylint/issues/5953>`_. This should be doable without any pylint or astroid knowledge, so this is the perfect entrypoint if you want to contribute to pylint or open source without any experience with our code!

Last but not least @clavedeluna and @nickdrozd became triagers, welcome to the team !

  What's new in Pylint 2.16.4?

Release date: 2023-03-06

  False Positives Fixed

•   Fix false positive for isinstance-second-argument-not-valid-type with union types.

    Closes #8205 (#8205)

  What's new in Pylint 2.16.3?

Release date: 2023-03-03

  False Positives Fixed

•   Fix false positive for wrong-spelling-in-comment with class names in a python 2 type comment.

    Closes #8370 (#8370)

  Other Bug Fixes

•   Prevent emitting invalid-name for the line on which a global statement is declared.

    Closes #8307 (#8307)

  What's new in Pylint 2.16.2?

Release date: 2023-02-13

  New Features

•   Add --version option to pyreverse.

    Refs #7851 (#7851)

  False Positives Fixed

•   Fix false positive for used-before-assignment when typing.TYPE_CHECKING is used with if/elif/else blocks.

    Closes #7574 (#7574)

•   Fix false positive for used-before-assignment for named expressions appearing after the first element in a list, tuple, or set.

    Closes #8252 (#8252)

  Other Bug Fixes

•   Fix used-before-assignment false positive when the walrus operator is used with a ternary operator in dictionary key/value initialization.

    Closes #8125 (#8125)

•   Fix no-name-in-module false positive raised when a package defines a variable with the same name as one of its submodules.

    Closes #8148 (#8148)

•   Fix nested-min-max suggestion message to indicate it's possible to splat iterable objects.

    Closes #8168 (#8168)

•   Fix a crash happening when a class attribute was negated in the start argument of an enumerate.

    Closes #8207 (#8207)

  What's new in Pylint 2.16.1?

Release date: 2023-02-02

  Other Bug Fixes

•   Fix a crash happening for python interpreter < 3.9 following a failed typing update.

    Closes #8161 (#8161)

  What's new in Pylint 2.16.0?

Release date: 2023-02-01

  Changes requiring user actions

•   The accept-no-raise-doc option related to missing-raises-doc will now be correctly taken into account all the time.

    Pylint will no longer raise missing-raises-doc (W9006) when no exceptions are documented and accept-no-raise-doc is true (issue #7208). If you were expecting missing-raises-doc errors to be raised in that case, you will now have to add accept-no-raise-doc=no in your configuration to keep the same behavior.

    Closes #7208 (#7208)

  New Features

•   Added the no-header output format. If enabled with --output-format=no-header, it will not include the module name in the output.

    Closes #5362 (#5362)

•   Added configuration option clear-cache-post-run to support server-like usage. Use this flag if you expect the linted files to be altered between runs.

    Refs #5401 (#5401)

•   Add --allow-reexport-from-package option to configure the useless-import-alias check not to emit a warning if a name is reexported from a package.

    Closes #6006 (#6006)

•   Update pyreverse to differentiate between aggregations and compositions. pyreverse checks if it's an Instance or a Call of an object via method parameters (via type hints) to decide if it's a composition or an aggregation.

    Refs #6543 (#6543)

  New Checks

•   Adds a pointless-exception-statement check that emits a warning when an Exception is created and not assigned, raised or returned.

    Refs #3110 (#3110)

•   Add a shadowed-import message for aliased imports.

    Closes #4836 (#4836)

•   Add new check called unbalanced-dict-unpacking to check for unbalanced dict unpacking in assignment and for loops.

    Closes #5797 (#5797)

•   Add new checker positional-only-arguments-expected to check for cases when positional-only arguments have been passed as keyword arguments.

    Closes #6489 (#6489)

•   Added singledispatch-method which informs that @singledispatch should decorate functions and not class/instance methods. Added singledispatchmethod-function which informs that @singledispatchmethod should decorate class/instance methods and not functions.

    Closes #6917 (#6917)

•   Rename broad-except to broad-exception-caught and add new checker broad-exception-raised which will warn if general exceptions BaseException or Exception are raised.

    Closes #7494 (#7494)

•   Added nested-min-max which flags min(1, min(2, 3)) to simplify to min(1, 2, 3).

    Closes #7546 (#7546)

•   Extended use-dict-literal to also warn about call to dict() when passing keyword arguments.

    Closes #7690 (#7690)

•   Add named-expr-without-context check to emit a warning if a named expression is used outside a context like if, for, while, or a comprehension.

    Refs #7760 (#7760)

•   Add invalid-slice-step check to warn about a slice step value of 0 for common builtin sequences.

    Refs #7762 (#7762)

•   Add consider-refactoring-into-while-condition check to recommend refactoring when a while loop is defined with a constant condition with an immediate if statement to check for break condition as a first statement.

    Closes #8015 (#8015)

  Extensions

•   Add new extension checker dict-init-mutate that flags mutating a dictionary immediately after the dictionary was created.

    Closes #2876 (#2876)

•   Added bad-dunder-name extension check, which flags bad or misspelled dunder methods. You can use the good-dunder-names option to allow specific dunder names.

    Closes #3038 (#3038)

•   Added consider-using-augmented-assign check for CodeStyle extension which flags x = x + 1 to simplify to x += 1. This check is disabled by default. To use it, load the code style extension with load-plugins=pylint.extensions.code_style and add consider-using-augmented-assign in the enable option.

    Closes #3391 (#3391)

•   Add magic-number plugin checker for comparison with constants instead of named constants or enums. You can use it with --load-plugins=pylint.extensions.magic_value.

    Closes #7281 (#7281)

•   Add redundant-typehint-argument message for typing plugin for duplicate assign typehints. Enable the plugin to enable the message with: --load-plugins=pylint.extensions.typing.

    Closes #7636 (#7636)

  False Positives Fixed

•   Fix false positive for unused-variable and unused-import when a name is only used in a string literal type annotation.

    Closes #3299 (#3299)

•   Document a known false positive for useless-suppression when disabling line-too-long in a module with only comments and no code.

    Closes #3368 (#3368)

•   trailing-whitespaces is no longer reported within strings.

    Closes #3822 (#3822)

•   Fix false positive for global-variable-not-assigned when a global variable is re-assigned via an ImportFrom node.

    Closes #4809 (#4809)

•   Fix false positive for use-maxsplit-arg with custom split method.

    Closes #4857 (#4857)

•   Fix logging-fstring-interpolation false positive raised when logging and f-string with %s formatting.

    Closes #4984 (#4984)

•   Fix false-positive for used-before-assignment in pattern matching with a guard.

    Closes #5327 (#5327)

•   Fix use-sequence-for-iteration when unpacking a set with *.

    Closes #5788 (#5788)

•   Fix deprecated-method false positive when alias for method is similar to name of deprecated method.

    Closes #5886 (#5886)

•   Fix false positive assigning-non-slot when a class attribute is re-assigned.

    Closes #6001 (#6001)

•   Fix false positive for too-many-function-args when a function call is assigned to a class attribute inside the class where the function is defined.

    Closes #6592 (#6592)

•   Fixes false positive abstract-method on Protocol classes.

    Closes #7209 (#7209)

•   Pylint now understands the kw_only keyword argument for dataclass.

    Closes #7290, closes #6550, closes #5857 (#7290)

•   Fix false positive for undefined-loop-variable in for-else loops that use a function having a return type annotation of NoReturn or Never.

    Closes #7311 (#7311)

•   Fix used-before-assignment for functions/classes defined in type checking guard.

    Closes #7368 (#7368)

•   Fix false positive for unhashable-member when subclassing dict and using the subclass as a dictionary key.

    Closes #7501 (#7501)

•   Fix the message for unnecessary-dunder-call for __aiter__ and __aneext__. Also only emit the warning when py-version >= 3.10.

    Closes #7529 (#7529)

•   Fix used-before-assignment false positive when else branch calls sys.exit or similar terminating functions.

    Closes #7563 (#7563)

•   Fix a false positive for used-before-assignment for imports guarded by typing.TYPE_CHECKING later used in variable annotations.

    Closes #7609 (#7609)

•   Fix a false positive for simplify-boolean-expression when multiple values are inferred for a constant.

    Closes #7626 (#7626)

•   unnecessary-list-index-lookup will not be wrongly emitted if enumerate is called with start.

    Closes #7682 (#7682)

•   Don't warn about stop-iteration-return when using next() over itertools.cycle.

    Closes #7765 (#7765)

•   Fixes used-before-assignment false positive when the walrus operator is used in a ternary operator.

    Closes #7779 (#7779)

•   Fix missing-param-doc false positive when function parameter has an escaped underscore.

    Closes #7827 (#7827)

•   Fixes method-cache-max-size-none false positive for methods inheriting from Enum.

    Closes #7857 (#7857)

•   multiple-statements no longer triggers for function stubs using inlined ....

    Closes #7860 (#7860)

•   Fix a false positive for used-before-assignment when a name guarded by if TYPE_CHECKING: is used as a type annotation in a function body and later re-imported in the same scope.

    Closes #7882 (#7882)

•   Prevent used-before-assignment when imports guarded by if TYPE_CHECKING are guarded again when used.

    Closes #7979 (#7979)

•   Fixes false positive for try-except-raise with multiple exceptions in one except statement if exception are in different namespace.

    Closes #8051 (#8051)

•   Fix invalid-name errors for typing_extension.TypeVar.

    Refs #8089 (#8089)

•   Fix no-kwoa false positive for context managers.

    Closes #8100 (#8100)

•   Fix a false positive for redefined-variable-type when async methods are present.

    Closes #8120 (#8120)

  False Negatives Fixed

•   Code following a call to quit, exit, sys.exit or os._exit will be marked as unreachable.

    Refs #519 (#519)

•   Emit used-before-assignment when function arguments are redefined inside an inner function and accessed there before assignment.

    Closes #2374 (#2374)

•   Fix a false negative for unused-import when one module used an import in a type annotation that was also used in another module.

    Closes #4150 (#4150)

•   Flag superfluous-parens if parentheses are used during string concatenation.

    Closes #4792 (#4792)

•   Emit used-before-assignment when relying on names only defined under conditions always testing false.

    Closes #4913 (#4913)

•   consider-using-join can now be emitted for non-empty string separators.

    Closes #6639 (#6639)

•   Emit used-before-assignment for further imports guarded by TYPE_CHECKING

    Previously, this message was only emitted for imports guarded directly under TYPE_CHECKING, not guarded two if-branches deep, nor when TYPE_CHECKING was imported from typing under an alias.

    Closes #7539 (#7539)

•   Fix a false negative for unused-import when a constant inside typing.Annotated was treated as a reference to an import.

    Closes #7547 (#7547)

•   consider-using-any-or-all message will now be raised in cases when boolean is initialized, reassigned during loop, and immediately returned.

    Closes #7699 (#7699)

•   Extend invalid-slice-index to emit an warning for invalid slice indices used with string and byte sequences, and range objects.

    Refs #7762 (#7762)

•   Fixes unnecessary-list-index-lookup false negative when enumerate is called with iterable as a kwarg.

    Closes #7770 (#7770)

•   no-else-return or no-else-raise will be emitted if except block always returns or raises.

    Closes #7788 (#7788)

•   Fix dangerous-default-value false negative when * is used.

    Closes #7818 (#7818)

•   consider-using-with now triggers for pathlib.Path.open.

    Closes #7964 (#7964)

  Other Bug Fixes

•   Fix bug in detecting unused-variable when iterating on variable.

    Closes #3044 (#3044)

•   Fix bug in scanning of names inside arguments to typing.Literal. See https://peps.python.org/pep-0586/#literals-enums-and-forward-references for details.

    Refs #3299 (#3299)

•   Update disallowed-name check to flag module-level variables.

    Closes #3701 (#3701)

•   Pylint will no longer deadlock if a parallel job is killed but fail immediately instead.

    Closes #3899 (#3899)

•   Fix ignored files being linted when passed on stdin.

    Closes #4354 (#4354)

•   Fix no-member false negative when augmented assign is done manually, without +=.

    Closes #4562 (#4562)

•   Any assertion on a populated tuple will now receive a assert-on-tuple warning.

    Closes #4655 (#4655)

•   missing-return-doc, missing-raises-doc and missing-yields-doc now respect the no-docstring-rgx option.

    Closes #4743 (#4743)

•   Update reimported help message for clarity.

    Closes #4836 (#4836)

•   consider-iterating-dictionary will no longer be raised if bitwise operations are used.

    Closes #5478 (#5478)

•   Using custom braces in msg-template will now work properly.

    Closes #5636 (#5636)

•   Pylint will now filter duplicates given to it before linting. The output should be the same whether a file is given/discovered multiple times or not.

    Closes #6242, #4053 (#6242)

•   Remove __index__ dunder method call from unnecessary-dunder-call check.

    Closes #6795 (#6795)

•   Fixed handling of -- as separator between positional arguments and flags. This was not actually fixed in 2.14.5.

    Closes #7003, Refs #7096 (#7003)

•   Don't crash on OSError in config file discovery.

    Closes #7169 (#7169)

•   Messages sent to reporter are now copied so a reporter cannot modify the message sent to other reporters.

    Closes #7214 (#7214)

•   Fixed a case where custom plugins specified by command line could silently fail.

    Specifically, if a plugin relies on the init-hook option changing sys.path before it can be imported, this will now emit a bad-plugin-value message. Before this change, it would silently fail to register the plugin for use, but would load any configuration, which could have unintended effects.

    Fixes part of #7264. (#7264)

•   Update modified_iterating checker to fix a crash with for loops on empty list.

    Closes #7380 (#7380)

•   Update wording for arguments-differ and arguments-renamed to clarify overriding object.

    Closes #7390 (#7390)

•   disable-next is now correctly scoped to only the succeeding line.

    Closes #7401 (#7401)

•   Fixed a crash in the unhashable-member checker when using a lambda as a dict key.

    Closes #7453 (#7453)

•   Add mailcap to deprecated modules list.

    Closes #7457 (#7457)

•   Fix a crash in the modified-iterating-dict checker involving instance attributes.

    Closes #7461 (#7461)

•   invalid-class-object does not crash anymore when __class__ is assigned alongside another variable.

    Closes #7467 (#7467)

•   --help-msg now accepts a comma-separated list of message IDs again.

    Closes #7471 (#7471)

•   Allow specifying non-builtin exceptions in the overgeneral-exception option using an exception's qualified name.

    Closes #7495 (#7495)

•   Report no-self-argument rather than no-method-argument for methods with variadic arguments.

    Closes #7507 (#7507)

•   Fixed an issue where syntax-error couldn't be raised on files with invalid encodings.

    Closes #7522 (#7522)

•   Fix false positive for redefined-outer-name when aliasing typing e.g. as t and guarding imports under t.TYPE_CHECKING.

    Closes #7524 (#7524)

•   Fixed a crash of the modified_iterating checker when iterating on a set defined as a class attribute.

    Closes #7528 (#7528)

•   Use py-version to determine if a message should be emitted for messages defined with max-version or min-version.

    Closes #7569 (#7569)

•   Improve bad-thread-instantiation check to warn if target is not passed in as a keyword argument or as a second argument.

    Closes #7570 (#7570)

•   Fixes edge case of custom method named next raised an astroid error.

    Closes #7610 (#7610)

•   Fixed a multi-processing crash that prevents using any more than 1 thread on MacOS.

    The returned module objects and errors that were cached by the linter plugin loader cannot be reliably pickled. This means that dill would throw an error when attempting to serialise the linter object for multi-processing use.

    Closes #7635. (#7635)

•   Fix crash that happened when parsing files with unexpected encoding starting with 'utf' like utf13.

    Closes #7661 (#7661)

•   Fix a crash when a child class with an __init__ method inherits from a parent class with an __init__ class attribute.

    Closes #7742 (#7742)

•   Fix valid-metaclass-classmethod-first-arg default config value from "cls" to "mcs" which would cause both a false-positive and false-negative.

    Closes #7782 (#7782)

•   Fixes a crash in the unnecessary_list_index_lookup check when using enumerate with start and a class attribute.

    Closes #7821 (#7821)

•   Fixes a crash in stop-iteration-return when the next builtin is called without arguments.

    Closes #7828 (#7828)

•   When pylint exit due to bad arguments being provided the exit code will now be the expected 32.

    Refs #7931 (#7931)

•   Fixes a ModuleNotFound exception when running pylint on a Django project with the pylint_django plugin enabled.

    Closes #7938 (#7938)

•   Fixed a crash when inferring a value and using its qname on a slice that was being incorrectly called.

    Closes #8067 (#8067)

•   Use better regex to check for private attributes.

    Refs #8081 (#8081)

•   Fix issue with new typing Union syntax in runtime context for Python 3.10+.

    Closes #8119 (#8119)

  Other Changes

•   Pylint now provides basic support for Python 3.11.

    Closes #5920 (#5920)

•   Update message for abstract-method to include child class name.

    Closes #7124 (#7124)

•   Update Pyreverse's dot and plantuml printers to detect when class methods are abstract and show them with italic font. For the dot printer update the label to use html-like syntax.

    Closes #7346 (#7346)

•   The docparams extension now considers typing in Numpy style docstrings as "documentation" for the missing-param-doc message.

    Refs #7398 (#7398)

•   Relevant DeprecationWarnings are now raised with stacklevel=2, so they have the callsite attached in the message.

    Closes #7463 (#7463)

•   Add a minimal option to pylint-config and its toml generator.

    Closes #7485 (#7485)

•   Add method name to the error messages of no-method-argument and no-self-argument.

    Closes #7507 (#7507)

•   Prevent leaving the pip install cache in the Docker image.

    Refs #7544 (#7544)

•   Add a keyword-only compare_constants argument to safe_infer.

    Refs #7626 (#7626)

•   Add default_enabled option to optional message dict. Provides an option to disable a checker message by default. To use a disabled message, the user must enable it explicitly by adding the message to the enable option.

    Refs #7629 (#7629)

•   Sort --generated-rcfile output.

    Refs #7655 (#7655)

•   epylint is now deprecated and will be removed in pylint 3.0.0. All emacs and flymake related files were removed and their support will now happen in an external repository : https://github.com/emacsorphanage/pylint.

    Closes #7737 (#7737)

•   Adds test for existing preferred-modules configuration functionality.

    Refs #7957 (#7957)

  Internal Changes

•   Add and fix regression tests for plugin loading.

    This shores up the tests that cover the loading of custom plugins as affected by any changes made to the sys.path during execution of an init-hook. Given the existing contract of allowing plugins to be loaded by fiddling with the path in this way, this is now the last bit of work needed to close Github issue #7264.

    Closes #7264 (#7264)

  What's New in Pylint 2.15

Release
    2.15

Date
    2022-08-26

  Summary -- Release highlights

In pylint 2.15.0, we added a new check missing-timeout to warn of default timeout values that could cause a program to be hanging indefinitely.

We improved pylint's handling of namespace packages. More packages should be linted without resorting to using the --recursive=y option.

We still welcome any community effort to help review, integrate, and add good/bad examples to the doc for <https://github.com/PyCQA/pylint/issues/5953>`_. This should be doable without any pylint or astroid knowledge, so this is the perfect entrypoint if you want to contribute to pylint or open source without any experience with our code!

Internally, we changed the way we generate the release notes, thanks to DudeNr33. There will be no more conflict resolution to do in the changelog, and every contributor rejoice.

Marc Byrne became a maintainer, welcome to the team !

  What's new in Pylint 2.15.10?

Release date: 2023-01-09

  False Positives Fixed

•   Fix use-sequence-for-iteration when unpacking a set with *.

    Closes #5788 (#5788)

•   Fix false positive assigning-non-slot when a class attribute is re-assigned.

    Closes #6001 (#6001)

•   Fixes used-before-assignment false positive when the walrus operator is used in a ternary operator.

    Closes #7779 (#7779)

•   Prevent used-before-assignment when imports guarded by if TYPE_CHECKING are guarded again when used.

    Closes #7979 (#7979)

  Other Bug Fixes

•   Using custom braces in msg-template will now work properly.

    Closes #5636 (#5636)

  What's new in Pylint 2.15.9?

Release date: 2022-12-17

  False Positives Fixed

•   Fix false-positive for used-before-assignment in pattern matching with a guard.

    Closes #5327 (#5327)

  Other Bug Fixes

•   Pylint will no longer deadlock if a parallel job is killed but fail immediately instead.

    Closes #3899 (#3899)

•   When pylint exit due to bad arguments being provided the exit code will now be the expected 32.

    Refs #7931 (#7931)

•   Fixes a ModuleNotFound exception when running pylint on a Django project with the pylint_django plugin enabled.

    Closes #7938 (#7938)

  What's new in Pylint 2.15.8?

Release date: 2022-12-05

  False Positives Fixed

•   Document a known false positive for useless-suppression when disabling line-too-long in a module with only comments and no code.

    Closes #3368 (#3368)

•   Fix logging-fstring-interpolation false positive raised when logging and f-string with %s formatting.

    Closes #4984 (#4984)

•   Fixes false positive abstract-method on Protocol classes.

    Closes #7209 (#7209)

•   Fix missing-param-doc false positive when function parameter has an escaped underscore.

    Closes #7827 (#7827)

•   multiple-statements no longer triggers for function stubs using inlined ....

    Closes #7860 (#7860)

  What's new in Pylint 2.15.7?

Release date: 2022-11-27

  False Positives Fixed

•   Fix deprecated-method false positive when alias for method is similar to name of deprecated method.

    Closes #5886 (#5886)

•   Fix a false positive for used-before-assignment for imports guarded by typing.TYPE_CHECKING later used in variable annotations.

    Closes #7609 (#7609)

  Other Bug Fixes

•   Pylint will now filter duplicates given to it before linting. The output should be the same whether a file is given/discovered multiple times or not.

    Closes #6242, #4053 (#6242)

•   Fixes a crash in stop-iteration-return when the next builtin is called without arguments.

    Closes #7828 (#7828)

  What's new in Pylint 2.15.6?

Release date: 2022-11-19

  False Positives Fixed

•   Fix false positive for unhashable-member when subclassing dict and using the subclass as a dictionary key.

    Closes #7501 (#7501)

•   unnecessary-list-index-lookup will not be wrongly emitted if enumerate is called with start.

    Closes #7682 (#7682)

•   Don't warn about stop-iteration-return when using next() over itertools.cycle.

    Closes #7765 (#7765)

  Other Bug Fixes

•   Messages sent to reporter are now copied so a reporter cannot modify the message sent to other reporters.

    Closes #7214 (#7214)

•   Fixes edge case of custom method named next raised an astroid error.

    Closes #7610 (#7610)

•   Fix crash that happened when parsing files with unexpected encoding starting with 'utf' like utf13.

    Closes #7661 (#7661)

•   Fix a crash when a child class with an __init__ method inherits from a parent class with an __init__ class attribute.

    Closes #7742 (#7742)

  What's new in Pylint 2.15.5?

Release date: 2022-10-21

  False Positives Fixed

•   Fix a false positive for simplify-boolean-expression when multiple values are inferred for a constant.

    Closes #7626 (#7626)

  Other Bug Fixes

•   Remove __index__ dunder method call from unnecessary-dunder-call check.

    Closes #6795 (#6795)

•   Fixed a multi-processing crash that prevents using any more than 1 thread on MacOS.

    The returned module objects and errors that were cached by the linter plugin loader cannot be reliably pickled. This means that dill would throw an error when attempting to serialise the linter object for multi-processing use.

    Closes #7635. (#7635)

  Other Changes

•   Add a keyword-only compare_constants argument to safe_infer.

    Refs #7626 (#7626)

•   Sort --generated-rcfile output.

    Refs #7655 (#7655)

  What's new in Pylint 2.15.4?

Release date: 2022-10-10

  False Positives Fixed

•   Fix the message for unnecessary-dunder-call for __aiter__ and __anext__. Also only emit the warning when py-version >= 3.10.

    Closes #7529 (#7529)

  Other Bug Fixes

•   Fix bug in detecting unused-variable when iterating on variable.

    Closes #3044 (#3044)

•   Fixed handling of -- as separator between positional arguments and flags. This was not actually fixed in 2.14.5.

    Closes #7003, Refs #7096 (#7003)

•   Report no-self-argument rather than no-method-argument for methods with variadic arguments.

    Closes #7507 (#7507)

•   Fixed an issue where syntax-error couldn't be raised on files with invalid encodings.

    Closes #7522 (#7522)

•   Fix false positive for redefined-outer-name when aliasing typing e.g. as t and guarding imports under t.TYPE_CHECKING.

    Closes #7524 (#7524)

•   Fixed a crash of the modified_iterating checker when iterating on a set defined as a class attribute.

    Closes #7528 (#7528)

•   Fix bug in scanning of names inside arguments to typing.Literal. See https://peps.python.org/pep-0586/#literals-enums-and-forward-references for details.

    Refs #3299 (#3299)

  Other Changes

•   Add method name to the error messages of no-method-argument and no-self-argument.

    Closes #7507 (#7507)

  What's new in Pylint 2.15.3?

Release date: 2022-09-19

•   Fixed a crash in the unhashable-member checker when using a lambda as a dict key.

    Closes #7453 (#7453)

•   Fix a crash in the modified-iterating-dict checker involving instance attributes.

    Closes #7461 (#7461)

•   invalid-class-object does not crash anymore when __class__ is assigned alongside another variable.

    Closes #7467 (#7467)

•   Fix false positive for global-variable-not-assigned when a global variable is re-assigned via an ImportFrom node.

    Closes #4809 (#4809)

•   Fix false positive for undefined-loop-variable in for-else loops that use a function having a return type annotation of NoReturn or Never.

    Closes #7311 (#7311)

•   --help-msg now accepts a comma-separated list of message IDs again.

    Closes #7471 (#7471)

  What's new in Pylint 2.15.2?

Release date: 2022-09-07

•   Fixed a case where custom plugins specified by command line could silently fail.

    Specifically, if a plugin relies on the init-hook option changing sys.path before it can be imported, this will now emit a bad-plugin-value message. Before this change, it would silently fail to register the plugin for use, but would load any configuration, which could have unintended effects.

    Fixes part of #7264. (#7264)

•   Fix used-before-assignment for functions/classes defined in type checking guard.

    Closes #7368 (#7368)

•   Update modified_iterating checker to fix a crash with for loops on empty list.

    Closes #7380 (#7380)

•   The docparams extension now considers typing in Numpy style docstrings as "documentation" for the missing-param-doc message.

    Refs #7398 (#7398)

•   Fix false positive for unused-variable and unused-import when a name is only used in a string literal type annotation.

    Closes #3299 (#3299)

•   Fix false positive for too-many-function-args when a function call is assigned to a class attribute inside the class where the function is defined.

    Closes #6592 (#6592)

•   Fix used-before-assignment for functions/classes defined in type checking guard.

    Closes #7368 (#7368)

•   Fix ignored files being linted when passed on stdin.

    Closes #4354 (#4354)

•   missing-return-doc, missing-raises-doc and missing-yields-doc now respect the no-docstring-rgx option.

    Closes #4743 (#4743)

•   Don't crash on OSError in config file discovery.

    Closes #7169 (#7169)

•   disable-next is now correctly scoped to only the succeeding line.

    Closes #7401 (#7401)

•   Update modified_iterating checker to fix a crash with for loops on empty list.

    Closes #7380 (#7380)

  What's new in Pylint 2.15.1?

Release date: 2022-09-06

This is a "github only release", it was mistakenly released as 2.16.0-dev on pypi. Replaced by 2.15.2.

  What's new in Pylint 2.15.0?

  New Checks

•   Added new checker missing-timeout to warn of default timeout values that could cause a program to be hanging indefinitely.

    Refs #6780 (#6780)

  False Positives Fixed

•   Don't report super-init-not-called for abstract __init__ methods.

    Closes #3975 (#3975)

•   Don't report unsupported-binary-operation on Python <= 3.9 when using the | operator with types, if one has a metaclass that overloads __or__ or __ror__ as appropriate.

    Closes #4951 (#4951)

•   Don't report no-value-for-parameter for dataclasses fields annotated with KW_ONLY.

    Closes #5767 (#5767)

•   Fixed inference of Enums when they are imported under an alias.

    Closes #5776 (#5776)

•   Prevent false positives when accessing PurePath.parents by index (not slice) on Python 3.10+.

    Closes #5832 (#5832)

•   unnecessary-list-index-lookup is now more conservative to avoid potential false positives.

    Closes #6896 (#6896)

•   Fix double emitting trailing-whitespace for multi-line docstrings.

    Closes #6936 (#6936)

•   import-error now correctly checks for contextlib.suppress guards on import statements.

    Closes #7270 (#7270)

•   Fix false positive for no-self-argument/no-method-argument when a staticmethod is applied to a function but uses a different name.

    Closes #7300 (#7300)

•   Fix undefined-loop-variable with break and continue statements in else blocks.

    Refs #7311 (#7311)

•   Improve default TypeVar name regex. Disallow names prefixed with T. E.g. use AnyStrT instead of TAnyStr.

    Refs #7322 (#7322 <https://github.com/PyCQA/pylint/issues/7322>`_)

  False Negatives Fixed

•   Emit used-before-assignment when relying on a name that is reimported later in a function.

    Closes #4624 (#4624)

•   Emit used-before-assignment for self-referencing named expressions (:=) lacking prior assignments.

    Closes #5653 (#5653)

•   Emit used-before-assignment for self-referencing assignments under if conditions.

    Closes #6643 (#6643)

•   Emit modified-iterating-list and analogous messages for dicts and sets when iterating literals, or when using the del keyword.

    Closes #6648 (#6648)

•   Emit used-before-assignment when calling nested functions before assignment.

    Closes #6812 (#6812)

•   Emit nonlocal-without-binding when a nonlocal name has been assigned at a later point in the same scope.

    Closes #6883 (#6883)

•   Emit using-constant-test when testing the truth value of a variable or call result holding a generator.

    Closes #6909 (#6909)

•   Rename unhashable-dict-key to unhashable-member and emit when creating sets and dicts, not just when accessing dicts.

    Closes #7034, Closes #7055 (#7034)

  Other Bug Fixes

•   Fix a failure to lint packages with __init__.py contained in directories lacking __init__.py.

    Closes #1667 (#1667)

•   Fixed a syntax-error crash that was not handled properly when the declared encoding of a file was utf-9.

    Closes #3860 (#3860)

•   Fix a crash in the not-callable check when there is ambiguity whether an instance is being incorrectly provided to __new__().

    Closes #7109 (#7109)

•   Fix crash when regex option raises a re.error exception.

    Closes #7202 (#7202)

•   Fix undefined-loop-variable from walrus in comprehension test.

    Closes #7222 (#7222)

•   Check for <cwd> before removing first item from sys.path in modify_sys_path.

    Closes #7231 (#7231)

•   Fix sys.path pollution in parallel mode.

    Closes #7246 (#7246)

•   Prevent useless-parent-delegation for delegating to a builtin written in C (e.g. Exception.__init__) with non-self arguments.

    Closes #7319 (#7319)

  Other Changes

•   bad-exception-context has been renamed to bad-exception-cause as it is about the cause and not the context.

    Closes #3694 (#3694)

•   The message for literal-comparison is now more explicit about the problem and the solution.

    Closes #5237 (#5237)

•   useless-super-delegation has been renamed to useless-parent-delegation in order to be more generic.

    Closes #6953 (#6953)

•   Pylint now uses towncrier for changelog generation.

    Refs #6974 (#6974)

•   Update astroid to 2.12.

    Refs #7153 (#7153)

•   Fix crash when a type-annotated __slots__ with no value is declared.

    Closes #7280 (#7280)

  Internal Changes

•   Fixed an issue where it was impossible to update functional tests output when the existing output was impossible to parse. Instead of raising an error we raise a warning message and let the functional test fail with a default value.

    Refs #6891 (#6891)

•   pylint.testutils.primer is now a private API.

    Refs #6905 (#6905)

•   We changed the way we handle the changelog internally by using towncrier. If you're a contributor you won't have to fix merge conflicts in the changelog anymore.

    Closes #6974 (#6974)

•   Pylint is now using Scorecards to implement security recommendations from the OpenSSF. This is done in order to secure our supply chains using a combination of automated tooling and best practices, most of which were already implemented before.

    Refs #7267 (#7267)

  What's New in Pylint 2.14

From pylint's beginning to pylint 2.14.0 included, we had a changelog that contained all nontrivial changes to Pylint, including changes that were not user facing, i.e. change that might interest you only if you're a developer working on pylint or pylint plugins or an open-source historian.

From pylint 1.6.0 to 2.14.0, on top of the full changelog there was also a summary of (mostly user facing) changes.

  Summary -- Release highlights

With 2.14 pylint only supports Python version 3.7.2 and above.

We introduced several new checks among which duplicate-value for sets, comparison-of-constants, and checks related to lambdas. We removed no-init and made no-self-use optional as they were too opinionated. We also added an option to generate a toml configuration: --generate-toml-config.

We migrated to argparse from optparse and refactored the configuration handling thanks to Daniël van Noord. On the user side it should change the output of the --help command, and some inconsistencies and bugs should disappear. The behavior between options set in a config file versus on the command line will be more consistent. For us, it will permit to maintain this part of the code easily in the future and anticipate optparse's removal in Python 3.12.

As a result of the refactor there are a lot of internal deprecations. If you're a library maintainer that depends on pylint, please verify that you're ready for pylint 3.0 by activating deprecation warnings.

We continued the integration of pylint-error and are now at 33%!. We still welcome any community effort to help review, integrate, and add good/bad examples <https://github.com/PyCQA/pylint/issues/5953>`_. This should be doable without any pylint or astroid knowledge, so this is the perfect entrypoint if you want to contribute to pylint or open source without any experience with our code!

  New checkers

•   Added new checker comparison-of-constants.

    Closes #6076

•   Added new checker typevar-name-mismatch: TypeVar must be assigned to a variable with the same name as its name argument.

    Closes #5224

•   invalid-enum-extension: Used when a class tries to extend an inherited Enum class.

    Closes #5501

•   Added new checker typevar-double-variance: The "covariant" and "contravariant" keyword arguments cannot both be set to "True" in a TypeVar.

    Closes #5895

•   Add new check unnecessary-dunder-call for unnecessary dunder method calls.

    Closes #5936

•   unnecessary-lambda-assignment: Lambda expression assigned to a variable. Define a function using the "def" keyword instead. unnecessary-direct-lambda-call: Lambda expression called directly. Execute the expression inline instead.

    Closes #5976

•   potential-index-error: Emitted when the index of a list or tuple exceeds its length. This checker is currently quite conservative to avoid false positives. We welcome suggestions for improvements.

    Closes #578

•   Added new checker unnecessary-list-index-lookup for indexing into a list while iterating over enumerate().

    Closes #4525

•   Added new message called duplicate-value which identifies duplicate values inside sets.

    Closes #5880

•   Added the super-without-brackets checker, raised when a super call is missing its brackets.

    Closes #4008

  Removed checkers

•   The no-init (W0232) warning has been removed. It's ok to not have an __init__ in a class.

    Closes #2409

•   Removed the assign-to-new-keyword message as there are no new keywords in the supported Python versions any longer.

    Closes #4683

•   Moved no-self-use check to optional extension. You now need to explicitly enable this check using load-plugins=pylint.extensions.no_self_use.

    Closes #5502

  Extensions

•   RedefinedLoopNameChecker

•   Added optional extension redefined-loop-name to emit messages when a loop variable is redefined in the loop body.

    Closes #5072

•   DocStringStyleChecker

•   Re-enable checker bad-docstring-quotes for Python <= 3.7.

    Closes #6087

•   NoSelfUseChecker

•   Added no-self-use check, previously enabled by default.

    Closes #5502

  Other Changes

•   Started ignoring underscore as a local variable for too-many-locals.

    Closes #6488

•   Pylint can now be installed with an extra-require called spelling (pip install pylint[spelling]). This will add pyenchant to pylint's dependencies. You will still need to install the requirements for pyenchant (the enchant library and any dictionaries) yourself. You will also need to set the spelling-dict option.

    Refs #6462

•   Improved wording of the message of deprecated-module

    Closes #6169

•   Pylint now requires Python 3.7.2 or newer to run.

    Closes #4301

•   We made a greater effort to reraise failures stemming from the astroid library as AstroidError, with the effect that pylint emits astroid-error rather than merely fatal. Regardless, please report any such issues you encounter!

•   We have improved our recognition of inline disable and enable comments. It is now possible to disable bad-option-value inline (as long as you disable it before the bad option value is raised, i.e. disable=bad-option-value,bad-message not disable=bad-message,bad-option-value ) as well as certain other previously unsupported messages.

    Closes #3312

•   The main checker name is now main instead of master. The configuration does not need to be updated as sections' name are optional.

    Closes #5467

•   Update invalid-slots-object message to show bad object rather than its inferred value.

    Closes #6101

•   Fixed a crash in the not-an-iterable checker involving multiple starred expressions inside a call.

    Closes #6372

•   Fixed a crash in the unused-private-member checker involving chained private attributes.

    Closes #6709

•   Disable spellchecking of mypy rule names in ignore directives.

    Closes #5929

•   implicit-str-concat will now be raised on calls like open("myfile.txt" "a+b") too.

    Closes #6441

•   Fix a failure to respect inline disables for fixme occurring on the last line of a module when pylint is launched with --enable=fixme.

•   Removed the broken generate-man option.

    Closes #5283 Closes #1887

•   Fixed failure to enable deprecated-module after a disable=all by making ImportsChecker solely responsible for emitting deprecated-module instead of sharing responsibility with StdlibChecker. (This could have led to double messages.)

•   Added the generate-toml-config option.

    Refs #5462

•   bad-option-value will be emitted whenever a configuration value or command line invocation includes an unknown message.

    Closes #4324

•   Added the unrecognized-option message. Raised if we encounter any unrecognized options.

    Closes #5259

•   Fix false negative for bad-string-format-type if the value to be formatted is passed in as a variable holding a constant.

•   The concept of checker priority has been removed.

•   The cache-max-size-none checker has been renamed to method-cache-max-size-none.

    Closes #5670

•   The method-cache-max-size-none checker will now also check functools.cache.

    Closes #5670

•   BaseChecker classes now require the linter argument to be passed.

•   The set_config_directly decorator has been removed.

•   Don't report useless-super-delegation for the __hash__ method in classes that also override the __eq__ method.

    Closes #3934

•   Fix falsely issuing useless-suppression on the wrong-import-position checker.

    Closes #5219

•   Fixed false positive no-member for Enums with self-defined members.

    Closes #5138

•   Fix false negative for no-member when attempting to assign an instance attribute to itself without any prior assignment.

    Closes #1555

•   Changed message type from redefined-outer-name to redefined-loop-name (optional extension) for redefinitions of outer loop variables by inner loops.

    Closes #5608

•   By default the similarity checker will now ignore imports and ignore function signatures when computing duplication. If you want to keep the previous behaviour set ignore-imports and ignore-signatures to False.

•   Pylint now expands the user path (i.e. ~ to home/yusef/) and expands environment variables (i.e. home/$USER/$project to home/yusef/pylint for USER=yusef and project=pylint) for pyreverse's output-directory, import-graph, ext-import-graph, int-import-graph options, and the spell checker's spelling-private-dict-file option.

    Refs #6493

•   Don't emit unsubscriptable-object for string annotations. Pylint doesn't check if class is only generic in type stubs only.

    Closes #4369 and #6523

•   Fix pyreverse crash RuntimeError: dictionary changed size during iteration

    Refs #6612

•   Fix syntax for return type annotations in MermaidJS diagrams produced with pyreverse.

    Closes #6467

•   Fix type annotations of class and instance attributes using the alternative union syntax in pyreverse diagrams.

•   Fix bug where it writes a plain text error message to stdout, invalidating output formats.

    Closes #6597

•   The refactoring checker now also raises 'consider-using-a-generator' messages for max(), min() and sum().

    Refs #6595

•   Update ranges for using-constant-test and missing-parentheses-for-call-in-test error messages.

•   Don't emit no-member inside type annotations with from __future__ import annotations.

    Closes #6594

•   Fix unexpected-special-method-signature false positive for __init_subclass__ methods with one or more arguments.

    Closes #6644

  Deprecations

•   The ignore-mixin-members option has been deprecated. You should now use the new ignored-checks-for-mixins option.

    Closes #5205

•   interfaces.implements has been deprecated and will be removed in 3.0. Please use standard inheritance patterns instead of __implements__.

    Refs #2287

•   All Interface classes in pylint.interfaces have been deprecated. You can subclass the respective normal classes to get the same behaviour. The __implements__ functionality was based on a rejected PEP from 2001: https://peps.python.org/pep-0245/

    Closes #2287

•   MapReduceMixin has been deprecated. BaseChecker now implements get_map_data and reduce_map_data. If a checker actually needs to reduce data it should define get_map_data as returning something different than None and let its reduce_map_data handle a list of the types returned by get_map_data. An example can be seen by looking at pylint/checkers/similar.py.

•   The config attribute of BaseChecker has been deprecated. You can use checker.linter.config to access the global configuration object instead of a checker-specific object.

    Refs #5392

•   The level attribute of BaseChecker has been deprecated: everything is now displayed in --help, all the time.

    Refs #5392

•   The set_option method of BaseChecker has been deprecated. You can use checker.linter.set_option to set an option on the global configuration object instead of a checker-specific object.

    Refs #5392

•   The options_providers attribute of ArgumentsManager has been deprecated.

    Refs #5392

•   Fix saving of persistent data files in environments where the user's cache directory and the linted file are on a different drive.

    Closes #6394

•   The method-cache-max-size-none checker will now also check functools.cache.

•   The config attribute of PyLinter is now of the argparse.Namespace type instead of optparse.Values.

    Refs #5392

•   UnsupportedAction has been deprecated.

    Refs #5392

•   OptionsManagerMixIn has been deprecated.

    Refs #5392

•   OptionParser has been deprecated.

    Refs #5392

•   Option has been deprecated.

    Refs #5392

•   OptionsProviderMixIn has been deprecated.

    Refs #5392

•   ConfigurationMixIn has been deprecated.

•   The option_groups attribute of PyLinter has been deprecated.

    Refs #5392

•   get_global_config has been deprecated. You can now access all global options from checker.linter.config.

    Refs #5392

•   OptionsManagerMixIn has been replaced with ArgumentsManager. ArgumentsManager is considered private API and most methods that were public on OptionsManagerMixIn have now been deprecated and will be removed in a future release.

    Refs #5392

•   OptionsProviderMixIn has been replaced with ArgumentsProvider. ArgumentsProvider is considered private API and most methods that were public on OptionsProviderMixIn have now been deprecated and will be removed in a future release.

    Refs #5392

•   pylint.pyreverse.ASTWalker has been removed, as it was only used internally by a single child class.

    Refs #6712

•   pyreverse: Resolving and displaying implemented interfaces that are defined by the __implements__ attribute has been deprecated and will be removed in 3.0.

    Refs #6713

•   is_class_subscriptable_pep585_with_postponed_evaluation_enabled has been deprecated. Use is_postponed_evaluation_enabled(node) and is_node_in_type_annotation_context(node) instead.

    Refs #6536

  Full changelog

  What's New in Pylint 2.14.5?

Release date: 2022-07-17

•   Fixed a crash in the undefined-loop-variable check when enumerate() is used in a ternary expression.

    Closes #7131

•   Fixed handling of -- as separator between positional arguments and flags.

    Closes #7003

•   Fixed the disabling of fixme and its interaction with useless-suppression.

•   Allow lists of default values in parameter documentation for Numpy style.

    Closes #4035

  What's New in Pylint 2.14.4?

Release date: 2022-06-29

•   The differing-param-doc check was triggered by positional only arguments.

    Closes #6950

•   Fixed an issue where scanning . directory recursively with --ignore-path=^path/to/dir is not ignoring the path/to/dir directory.

    Closes #6964

•   Fixed regression that didn't allow quoted init-hooks in option files.

    Closes #7006

•   Fixed a false positive for modified-iterating-dict when updating an existing key.

    Closes #6179

•   Fixed an issue where many-core Windows machines (>~60 logical processors) would hang when using the default jobs count.

    Closes #6965

•   Fixed an issue with the recognition of setup.cfg files. Only .cfg files that are exactly named setup.cfg require section names that start with pylint..

    Closes #3630

•   Don't report import-private-name for relative imports.

    Closes #7078

  What's New in Pylint 2.14.3?

Release date: 2022-06-18

•   Fixed two false positives for bad-super-call for calls that refer to a non-direct parent.

    Closes #4922, Closes #2903

•   Fixed a false positive for useless-super-delegation for subclasses that specify the number of of parameters against a parent that uses a variadic argument.

    Closes #2270

•   Allow suppressing undefined-loop-variable and undefined-variable without raising useless-suppression.

•   Fixed false positive for undefined-variable for __class__ in inner methods.

    Closes #4032

  What's New in Pylint 2.14.2?

Release date: 2022-06-15

•   Fixed a false positive for unused-variable when a function returns an argparse.Namespace object.

    Closes #6895

•   Avoided raising an identical undefined-loop-variable message twice on the same line.

•   Don't crash if lint.run._query_cpu() is run within a Kubernetes Pod, that has only a fraction of a cpu core assigned. Just go with one process then.

    Closes #6902

•   Fixed a false positive in consider-using-f-string if the left side of a % is not a string.

    Closes #6689

•   Fixed a false positive in unnecessary-list-index-lookup and unnecessary-dict-index-lookup when the subscript is updated in the body of a nested loop.

    Closes #6818

•   Fixed an issue with multi-line init-hook options which did not record the line endings.

    Closes #6888

•   Fixed a false positive for used-before-assignment when a try block returns but an except handler defines a name via type annotation.

•   --errors-only no longer enables previously disabled messages. It was acting as "emit all and only error messages" without being clearly documented that way.

    Closes #6811

  What's New in Pylint 2.14.1?

Release date: 2022-06-06

•   Avoid reporting unnecessary-dict-index-lookup or unnecessary-list-index-lookup when the index lookup is part of a destructuring assignment.

    Closes #6788

•   Fixed parsing of unrelated options in tox.ini.

    Closes #6800

•   Fixed a crash when linting __new__() methods that return a call expression.

    Closes #6805

•   Don't crash if we can't find the user's home directory.

    Closes #6802

•   Fixed false positives for unused-import when aliasing typing e.g. as t and guarding imports under t.TYPE_CHECKING.

    Closes #3846

•   Fixed a false positive regression in 2.13 for used-before-assignment where it is safe to rely on a name defined only in an except block because the else block returned.

    Closes #6790

•   Fixed the use of abbreviations for some special options on the command line.

    Closes #6810

•   Fix a crash in the optional pylint.extensions.private_import extension.

    Closes #6624

•   bad-option-value (E0012) is now a warning unknown-option-value (W0012). Deleted messages that do not exist anymore in pylint now raise useless-option-value (R0022) instead of bad-option-value. This allows to distinguish between genuine typos and configuration that could be cleaned up. Existing message disables for bad-option-value will still work on both new messages.

    Refs #6794

  What's New in Pylint 2.14.0?

Release date: 2022-06-01

•   The refactoring checker now also raises 'consider-using-generator' messages for max(), min() and sum().

    Refs #6595

•   We have improved our recognition of inline disable and enable comments. It is now possible to disable bad-option-value inline (as long as you disable it before the bad option value is raised, i.e. disable=bad-option-value,bad-message not disable=bad-message,bad-option-value ) as well as certain other previously unsupported messages.

    Closes #3312

•   Fixed a crash in the unused-private-member checker involving chained private attributes.

    Closes #6709

•   Added new checker comparison-of-constants.

    Closes #6076

•   pylint.pyreverse.ASTWalker has been removed, as it was only used internally by a single child class.

    Refs #6712

•   pyreverse: Resolving and displaying implemented interfaces that are defined by the __implements__ attribute has been deprecated and will be removed in 3.0.

    Refs #6713

•   Fix syntax for return type annotations in MermaidJS diagrams produced with pyreverse.

    Closes #6467

•   Fix type annotations of class and instance attributes using the alternative union syntax in pyreverse diagrams.

•   Fix unexpected-special-method-signature false positive for __init_subclass__ methods with one or more arguments.

    Closes #6644

•   Started ignoring underscore as a local variable for too-many-locals.

    Closes #6488

•   Improved wording of the message of deprecated-module

    Closes #6169

•   Pylint now requires Python 3.7.2 or newer to run.

    Closes #4301

•   BaseChecker classes now require the linter argument to be passed.

•   Fix a failure to respect inline disables for fixme occurring on the last line of a module when pylint is launched with --enable=fixme.

•   Update invalid-slots-object message to show bad object rather than its inferred value.

    Closes #6101

•   The main checker name is now main instead of master. The configuration does not need to be updated as sections' name are optional.

    Closes #5467

•   Don't report useless-super-delegation for the __hash__ method in classes that also override the __eq__ method.

    Closes #3934

•   Added new checker typevar-name-mismatch: TypeVar must be assigned to a variable with the same name as its name argument.

    Closes #5224

•   Pylint can now be installed with an extra-require called spelling (pip install pylint[spelling]). This will add pyenchant to pylint's dependencies. You will still need to install the requirements for pyenchant (the enchant library and any dictionaries) yourself. You will also need to set the spelling-dict option.

    Refs #6462

•   Removed the assign-to-new-keyword message as there are no new keywords in the supported Python versions any longer.

    Closes #4683

•   Fixed a crash in the not-an-iterable checker involving multiple starred expressions inside a call.

    Closes #6372

•   Fixed a crash in the docparams extension involving raising the result of a function.

•   Fixed failure to enable deprecated-module after a disable=all by making ImportsChecker solely responsible for emitting deprecated-module instead of sharing responsibility with StdlibChecker. (This could have led to double messages.)

•   The no-init (W0232) warning has been removed. It's ok to not have an __init__ in a class.

    Closes #2409

•   The config attribute of BaseChecker has been deprecated. You can use checker.linter.config to access the global configuration object instead of a checker-specific object.

    Refs #5392

•   The level attribute of BaseChecker has been deprecated: everything is now displayed in --help, all the time.

    Refs #5392

•   The options_providers attribute of ArgumentsManager has been deprecated.

    Refs #5392

•   The option_groups attribute of PyLinter has been deprecated.

    Refs #5392

•   All Interface classes in pylint.interfaces have been deprecated. You can subclass the respective normal classes to get the same behaviour. The __implements__ functionality was based on a rejected PEP from 2001: https://peps.python.org/pep-0245/

    Closes #2287

•   The set_option method of BaseChecker has been deprecated. You can use checker.linter.set_option to set an option on the global configuration object instead of a checker-specific object.

    Refs #5392

•   implicit-str-concat will now be raised on calls like open("myfile.txt" "a+b") too.

    Closes #6441

•   The config attribute of PyLinter is now of the argparse.Namespace type instead of optparse.Values.

    Refs #5392

•   MapReduceMixin has been deprecated. BaseChecker now implements get_map_data and reduce_map_data. If a checker actually needs to reduce data it should define get_map_data as returning something different than None and let its reduce_map_data handle a list of the types returned by get_map_data. An example can be seen by looking at pylint/checkers/similar.py.

•   UnsupportedAction has been deprecated.

    Refs #5392

•   OptionsManagerMixIn has been deprecated.

    Refs #5392

•   OptionParser has been deprecated.

    Refs #5392

•   Option has been deprecated.

    Refs #5392

•   OptionsProviderMixIn has been deprecated.

    Refs #5392

•   ConfigurationMixIn has been deprecated.

    Refs #5392

•   get_global_config has been deprecated. You can now access all global options from checker.linter.config.

    Refs #5392

•   OptionsManagerMixIn has been replaced with ArgumentsManager. ArgumentsManager is considered private API and most methods that were public on OptionsManagerMixIn have now been deprecated and will be removed in a future release.

    Refs #5392

•   OptionsProviderMixIn has been replaced with ArgumentsProvider. ArgumentsProvider is considered private API and most methods that were public on OptionsProviderMixIn have now been deprecated and will be removed in a future release.

    Refs #5392

•   interfaces.implements has been deprecated and will be removed in 3.0. Please use standard inheritance patterns instead of __implements__.

    Refs #2287

•   invalid-enum-extension: Used when a class tries to extend an inherited Enum class.

    Closes #5501

•   Added the unrecognized-option message. Raised if we encounter any unrecognized options.

    Closes #5259

•   Added new checker typevar-double-variance: The "covariant" and "contravariant" keyword arguments cannot both be set to "True" in a TypeVar.

    Closes #5895

•   Re-enable checker bad-docstring-quotes for Python <= 3.7.

    Closes #6087

•   Removed the broken generate-man option.

    Closes #5283 Closes #1887

•   Fix false negative for bad-string-format-type if the value to be formatted is passed in as a variable holding a constant.

•   Add new check unnecessary-dunder-call for unnecessary dunder method calls.

    Closes #5936 Closes #6074

•   The cache-max-size-none checker has been renamed to method-cache-max-size-none.

    Closes #5670

•   The method-cache-max-size-none checker will now also check functools.cache.

    Closes #5670

•   unnecessary-lambda-assignment: Lambda expression assigned to a variable. Define a function using the "def" keyword instead. unnecessary-direct-lambda-call: Lambda expression called directly. Execute the expression inline instead.

    Closes #5976

•   potential-index-error: Emitted when the index of a list or tuple exceeds its length. This checker is currently quite conservative to avoid false positives. We welcome suggestions for improvements.

    Closes #578

•   Added optional extension redefined-loop-name to emit messages when a loop variable is redefined in the loop body.

    Closes #5072

•   Changed message type from redefined-outer-name to redefined-loop-name (optional extension) for redefinitions of outer loop variables by inner loops.

    Closes #5608

•   The ignore-mixin-members option has been deprecated. You should now use the new ignored-checks-for-mixins option.

    Closes #5205

•   bad-option-value will be emitted whenever a configuration value or command line invocation includes an unknown message.

    Closes #4324

•   Avoid reporting superfluous-parens on expressions using the is not operator.

    Closes #5930

•   Added the super-without-brackets checker, raised when a super call is missing its brackets.

    Closes #4008

•   Added the generate-toml-config option.

    Refs #5462

•   Added new checker unnecessary-list-index-lookup for indexing into a list while iterating over enumerate().

    Closes #4525

•   Fix falsely issuing useless-suppression on the wrong-import-position checker.

    Closes #5219

•   Fixed false positive no-member for Enums with self-defined members.

    Closes #5138

•   Fix false negative for no-member when attempting to assign an instance attribute to itself without any prior assignment.

    Closes #1555

•   The concept of checker priority has been removed.

•   Add a new command line option --minimal-messages-config for pytest, which disables all irrelevant messages when running the functional tests.

•   duplicate-argument-name now only raises once for each set of duplicated arguments.

•   Fix bug where specifically enabling just await-outside-async was not possible.

•   The set_config_directly decorator has been removed.

•   Added new message called duplicate-value which identifies duplicate values inside sets.

    Closes #5880

•   Pylint now expands the user path (i.e. ~ to home/yusef/) and expands environment variables (i.e. home/$USER/$project to home/yusef/pylint for USER=yusef and project=pylint) for pyreverse's output-directory, import-graph, ext-import-graph, int-import-graph options, and the spell checker's spelling-private-dict-file option.

    Refs #6493

•   Created NoSelfUseChecker extension and moved the no-self-use check. You now need to explicitly enable this check using load-plugins=pylint.extensions.no_self_use.

    Closes #5502

•   Fix saving of persistent data files in environments where the user's cache directory and the linted file are on a different drive.

    Closes #6394

•   Don't emit unsubscriptable-object for string annotations. Pylint doesn't check if class is only generic in type stubs only.

    Closes #4369 and #6523

•   Fix pyreverse crash RuntimeError: dictionary changed size during iteration

    Refs #6612

•   Fix bug where it writes a plain text error message to stdout, invalidating output formats.

    Closes #6597

•   is_class_subscriptable_pep585_with_postponed_evaluation_enabled has been deprecated. Use is_postponed_evaluation_enabled(node) and is_node_in_type_annotation_context(node) instead.

    Refs #6536

•   Update ranges for using-constant-test and missing-parentheses-for-call-in-test error messages.

•   Don't emit no-member inside type annotations with from __future__ import annotations.

    Closes #6594

  What's New in Pylint 2.13

From pylint's beginning to pylint 2.14.0 included, we had a changelog that contained all nontrivial changes to Pylint, including changes that were not user facing, i.e. change that might interest you only if you're a developer working on pylint or pylint plugins or an open-source historian.

From pylint 1.6.0 to 2.14.0, on top of the full changelog there was also a summary of (mostly user facing) changes.

  Summary -- Release highlights

In 2.13, we introduced a new check to deal with unicode security issues. On top of that a lot of work was done inside the unicode checker by @CarliJoy. We also introduced a new check when importing private name and for unnecessary ellipsis among other.

We fixed long standing issues related to duplicate code that could not be disabled, line numbers that were not accurate some of the time, and added the ability to lint all files in a directory without specifying each one. One of the most anticipated issue from the repository. Thank you @matusvalo !

A lot of undefined-variables and used-before-assignment issues were resolved thanks to @jacobtylerwalls.

We started integrating pylint-error the documentation created by @vald-phoenix a developer from Hlyniane, Ukraine. We hope he's doing well despite the current situation. The deployment is set up but there's still a lot to do so we welcome any community effort help to review, integrate, and add good/bad examples. This should be doable without any pylint or astroid knowledge, so this is the perfect entrypoint if you want to contribute to pylint without investing any time learning the internals.

This release is the last one to support interpreter below 3.7.2, 3.6 end of life was reached in december 2021.

  New checkers

•   Added several checkers to deal with unicode security issues (see Trojan Sources and PEP 672 for details) that also concern the readability of the code. In detail the following checks were added:

•   bad-file-encoding checks that the file is encoded in UTF-8 as suggested by PEP8. UTF-16 and UTF-32 are not supported by Python at the moment. If this ever changes invalid-unicode-codec checks that they aren't used, to allow for backwards compatibility.

•   bidirectional-unicode checks for bidirectional unicode characters that could make code execution different than what the user expects.

•   invalid-character-backspace, invalid-character-carriage-return, invalid-character-sub, invalid-character-esc, invalid-character-zero-width-space and invalid-character-nul to check for possibly harmful unescaped characters.

    Closes #5281

•   unnecessary-ellipsis: Emitted when the ellipsis constant is used unnecessarily.

    Closes #5460

•   Added new checker typevar-name-missing-variance. Emitted when a covariant or contravariant TypeVar does not end with _co or _contra respectively or when a TypeVar is not either but has a suffix.

•   Add modified-iterating-list, modified-iterating-dict, and modified-iterating-set, emitted when items are added to or removed from respectively a list, dictionary or set being iterated through.

    Closes #5348

•   Add checker redefined-slots-in-subclass: Emitted when a slot is redefined in a subclass.

    Closes #5617

•

Rewrote Checker of non-ascii-name.
    It now ensures __all__ Python names are ASCII and also properly checks the names of imports (non-ascii-module-import) as well as file names (non-ascii-file-name) and emits their respective new warnings.

    Non ASCII characters could be homoglyphs (look alike characters) and hard to enter on a non specialized keyboard. See Confusable Characters in PEP 672

•   Added cache-max-size-none checker with checks for the use of functools.lru_cache on class methods with a maxsize of None. This is unrecommended as it creates memory leaks by never letting the instance get garbage collected.

    Closes #5670 Clsoes #6180

  Removed checkers

•   Removed the deprecated check_docs extension. You can use the docparams checker to get the checks previously included in check_docs.

    Closes #5322

  Extensions

•   New extension import-private-name: indicate imports of external private packages and objects (prefixed with _). It can be loaded using load-plugins=pylint.extensions.private_import.

    Closes #5463

•   Pyreverse - add output in mermaid-js format and html which is an mermaid js diagram with html boilerplate

•   TypingChecker

•   Added new check broken-noreturn to detect broken uses of typing.NoReturn if py-version is set to Python 3.7.1 or below. https://bugs.python.org/issue34921

•   Added new check broken-collections-callable to detect broken uses of collections.abc.Callable if py-version is set to Python 3.9.1 or below. https://bugs.python.org/issue42965

•   DocstringParameterChecker

•   Fixed incorrect classification of Numpy-style docstring as Google-style docstring for docstrings with property setter documentation. Docstring classification is now based on the highest amount of matched sections instead of the order in which the docstring styles were tried.

•   DocStringStyleChecker

•   Disable checker bad-docstring-quotes for Python <= 3.7, because in these versions the line numbers for decorated functions and classes are not reliable which interferes with the checker.

    Closes #3077

  Other Changes

•   Include testing_pylintrc in source and wheel distributions.

    Closes #6028

•   Fix false positive for unused-import when disabling both used-before-assignment and undefined-variable.

    Closes #6089

•   Fix false positive for unnecessary-ellipsis when using an ellipsis as a default argument.

    Closes #5973

•   Add missing dunder methods to unexpected-special-method-signature check.

•   No longer emit no-member in for loops that reference self if the binary operation that started the for loop uses a self that is encapsulated in tuples or lists.

    Refs PyCQA/astroid#1360 Closes #4826

•   Fix matching --notes options that end in a non-word character.

    Closes #5840

•   The line numbering for messages related to function arguments is now more accurate. This can require some message disables to be relocated to updated positions.

•

using-f-string-in-unsupported-version and using-final-decorator-in-unsupported-version msgids
    were renamed from W1601 and W1602 to W2601 and W2602. Disables using these msgids will break. This is done in order to restore consistency with the already existing msgids for apply-builtin and basestring-builtin from the now deleted python 3K+ checker. There is now a check that we're not using existing msgids or symbols from deleted checkers.

    Closes #5729

•   Add --recursive option to allow recursive discovery of all modules and packages in subtree. Running pylint with --recursive=y option will check all discovered .py files and packages found inside subtree of directory provided as parameter to pylint.

    Closes #352

•   Updated the position of messages for class and function definitions to no longer cover the complete definition. Only the def or class + the name of the class/function are covered.

    Closes #5466

•   Reinstated checks from the python3 checker that are still useful for python 3 (eq-without-hash). This is now in the pylint.extensions.eq_without_hash optional extension.

    Closes #5025

•   Fix false-negative for assignment-from-none checker with list.sort() method.

    Closes #5722

•   Fix unused-private-member false positive when accessing private methods through property.

    Closes #4756

•   Fixed crash from arguments-differ and arguments-renamed when methods were defined outside the top level of a class.

    Closes #5648

•   Better warning messages for useless else or elif when a function returns early.

    Closes #5614

•   Asterisks are no longer required in Sphinx and Google style parameter documentation for missing-param-doc and are parsed correctly.

    Closes #5815 Closes #5406

•   Fixed an AstroidError in 2.13.0 raised by the `duplicate-code` checker with ignore-imports or ignore-signatures enabled.

    Closes #6301

•   Use the tomli package instead of toml to parse .toml files.

    Closes #5885

•   Fixed false positive consider-using-dict-comprehension when creating a dict using a list of tuples where key AND value vary depending on the same condition.

    Closes #5588

•   When run in parallel mode pylint now pickles the data passed to subprocesses with the dill package. The dill package has therefore been added as a dependency.

•   Fixed false positive for global-variable-undefined when global is used with a class name

    Closes #3088

•   Fixed crash on properties and inherited class methods when comparing them for equality against an empty dict.

    Closes #5646

•   By default, pylint does no longer take files starting with .# into account. Those are considered Emacs file locks. This behavior can be reverted by redefining the ignore-patterns option.

    Closes #367

•   Fix super-init-not-called when parent or self is a Protocol

    Closes #4790

•   The issue template for crashes is now created for crashes which were previously not covered by this mechanism.

    Closes #5668

•   An astroid issue where symlinks were not being taken into account was fixed

    Closes #1470 Closes #3499 Closes #4302 Closes #4798 Closes #5081

•   Fix false negative for undefined-variable and related variable messages when the same undefined variable is used as a type annotation and is accessed multiple times, or is used as a default argument to a function.

    Closes #5399

•   Emit used-before-assignment instead of undefined-variable when attempting to access unused type annotations.

    Closes #5713

•   Fixed an issue where ungrouped-imports could not be disabled without raising useless-suppression.

    Refs #2366

•   Fixed a crash on __init__ nodes when the attribute was previously uninferable due to a cache limit size. This limit can be hit when the inheritance pattern of a class (and therefore of the __init__ attribute) is very large.

    Closes #5679

•   Fixed extremely long processing of long lines with comma's.

    Closes #5483

•   Fix false positive super-init-not-called for classes that inherit their init from a parent.

    Closes #4941

•   Fix false positives for used-before-assignment from using named expressions in a ternary operator test and using that expression as a call argument.

    Closes #5177, #5212

•   Fixed crash with recursion error for inference of class attributes that referenced the class itself.

    Closes #5408 RefsPyCQA/astroid#1392

•   Fixed false positive for unused-argument when a method overridden in a subclass does nothing with the value of a keyword-only argument.

    Closes #5771 RefsPyCQA/astroid#1382

•   Optimize parsing of long lines when missing-final-newline is enabled.

    Closes #5724

•   Fix false positive for used-before-assignment from a class definition nested under a function subclassing a class defined outside the function.

    Closes #4590

•   Fix unnecessary_dict_index_lookup false positive when deleting a dictionary's entry.

    Closes #4716

•   Fix false positive for used-before-assignment when an except handler shares a name with a test in a filtered comprehension.

    Closes #5817

•   Fix a crash in unused-private-member checker when analyzing code using type(self) in bound methods.

    Closes #5569

•   Fix crash in unnecessary-dict-index-lookup checker if the output of items() is assigned to a 1-tuple.

    Closes #5504

•   Fixed crash with slots assignments and annotated assignments.

    Closes #5479

•   Fixed a crash in unspecified-encoding checker when providing None to the mode argument of an open() call.

    Closes #5731

•   Fixed a crash involving a NewType named with an f-string.

    Closes #5770 RefsPyCQA/astroid#1400

•   Improved bad-open-mode message when providing None to the mode argument of an open() call.

    Closes #5733

•   Fix false negative for consider-iterating-dictionary during membership checks encapsulated in iterables or not in checks

    Closes #5323

•   Allow disabling duplicate-code with a disable comment when running through pylint.

    Closes #214

•   Fix false positive for undefined-variable when namedtuple class attributes are used as return annotations.

    Closes #5568

•   Added confidence level CONTROL_FLOW for warnings relying on assumptions about control flow.

•   used-before-assignment now considers that assignments in a try block may not have occurred when the except or finally blocks are executed.

    Closes #85, #2615

•   Fixed false negative for used-before-assignment when a conditional or context manager intervened before the try statement that suggested it might fail.

    Closes #4045

•   Fixed false negative for used-before-assignment in finally blocks if an except handler did not define the assignment that might have failed in the try block.

•   Fix a false positive for assigning-non-slot when the slotted class defined __setattr__.

    Closes #3793

•   Fixed a false positive for invalid-class-object when the object being assigned to the __class__ attribute is uninferable.

•   Added a testutil extra require to the packaging, as gitpython should not be a dependency all the time but is still required to use the primer helper code in pylint.testutil. You can install it with pip install pylint[testutil].

    Closes #5486

•   Fixed a false positive for used-before-assignment when a named expression appears as the first value in a container.

    Closes #5112

•   Fixed false positive for used-before-assignment with self-referential type annotation in conditional statements within class methods.

    Closes #5499

•   used-before-assignment now assumes that assignments in except blocks may not have occurred and warns accordingly.

    Closes #4761

•   When evaluating statements after an except block, used-before-assignment assumes that assignments in the except blocks took place if the corresponding try block contained a return statement.

    Closes #5500

•   Fixed a false negative for used-before-assignment when some but not all except handlers defined a name relied upon after an except block when the corresponding try block contained a return statement.

    Closes #5524

•   When evaluating statements in the else clause of a loop, used-before-assignment assumes that assignments in the except blocks took place if the except handlers constituted the only ways for the loop to finish without breaking early.

    Closes #5683

•   used-before-assignment now checks names in try blocks.

•   Fixed false positive with used-before-assignment for assignment expressions in lambda statements.

    Closes #5360, #3877

•   Improve invalid-name check for TypeVar names. The accepted pattern can be customized with --typevar-rgx.

    Closes #3401

•   Fixed a false positive (affecting unreleased development) for used-before-assignment involving homonyms between filtered comprehensions and assignments in except blocks.

    Closes #5586

•   Fixed crash on list comprehensions that used type as inner variable name.

    Closes #5461

•   Fixed crash in use-maxsplit-arg checker when providing the sep argument to str.split() by keyword.

    Closes #5737

•   Fix false positive for unused-variable for a comprehension variable matching an outer scope type annotation.

    Closes #5326

•   Fix false negative for undefined-variable for a variable used multiple times in a comprehension matching an unused outer scope type annotation.

    Closes #5654

•   Require Python 3.6.2 to run pylint.

    Closes #5065

•   Fixed crash on uninferable decorators on Python 3.6 and 3.7

•   Emit redefined-outer-name when a nested except handler shadows an outer one.

    Closes #4434 Closes #5370

•   encoding can now be supplied as a positional argument to calls that open files without triggering unspecified-encoding.

    Closes #5638

•   Fatal errors now emit a score of 0.0 regardless of whether the linted module contained any statements

    Closes #5451

•   fatal was added to the variables permitted in score evaluation expressions.

•   The default score evaluation now uses a floor of 0.

    Closes #2399

•   Fix comparison-with-callable false positive for callables that raise, such as typing constants.

    Closes #5557

•   When invoking pylint, epylint, symilar or pyreverse by importing them in a python file you can now pass an argv keyword besides patching sys.argv.

    Closes #5320

•   The PyLinter class will now be initialized with a TextReporter as its reporter if none is provided.

•   Fix false positive not-callable with attributes that alias NamedTuple

    Fixes part of #1730

•   The testutils for unittests now accept end_lineno and end_column. Tests without these will trigger a DeprecationWarning.

•   arguments-differ will no longer complain about method redefinitions with extra parameters that have default values.

    Closes #1556, #5338

•   Disables for deprecated-module and similar warnings for stdlib features deprecated in newer versions of Python no longer raise useless-suppression when linting with older Python interpreters where those features are not yet deprecated.

•   Importing the deprecated stdlib module xml.etree.cElementTree now emits deprecated_module.

    Closes #5862

•   Importing the deprecated stdlib module distutils now emits deprecated_module on Python 3.10+.

•   Fixed false positive unexpected-keyword-arg for decorators.

    Closes #258

•   missing-raises-doc will now check the class hierarchy of the raised exceptions

    def my_function():
      """My function.
      Raises:
        Exception: if something fails
      """
      raise ValueError

    Closes #4955

•   Fixed false positive for unused-variable when a nonlocal name is assigned as part of a multi-name assignment.

    Closes #3781

•   Fix false positive - Allow unpacking of self in a subclass of typing.NamedTuple.

    Closes #5312

•   Fixed false negative unpacking-non-sequence when value is an empty list.

    Closes #5707

•   Fixed false positive for global-variable-not-assigned when the del statement is used

    Closes #5333

•   Fix type hints in class diagrams generated by pyreverse for class methods and methods returning None.

•   Output better error message if unsupported file formats are used with pyreverse.

    Closes #5950

•   Fixed false positive for unused-argument when a nonlocal name is used in a nested function that is returned without being called by its parent.

    Closes #5187

•   Avoid emitting raising-bad-type when there is inference ambiguity on the variable being raised.

    Closes #2793

•   Fix false positive for superfluous-parens for patterns like "return (a or b) in iterable".

    Closes #5803

•   Fix a crash in the unsupported-membership-test checker when assigning multiple constants to class attributes including __iter__ via unpacking.

    Closes #6366

•   Fix false positive for used-before-assignment for assignments taking place via nonlocal declarations after an earlier type annotation.

    Closes #5394

•   Fixed a false positive for unused-variable when a builtin specified in --additional-builtins is given a type annotation.

    Closes #6388

•   Fix false positive for 'nonexistent-operator' when repeated '-' are separated (e.g. by parens).

    Closes #5769

•   Fix a false positive for undefined-loop-variable when the else of a for loop raises or returns.

    Closes #5971

•   Only raise not-callable when all the inferred values of a property are not callable.

    Closes #5931

•   Fix false positive for unused-variable for classes inside functions and where a metaclass is provided via a call.

    Closes #4020

•   Avoid reporting superfluous-parens on expressions using the is not operator.

    Closes #5930

•   Fix a false positive for undefined-loop-variable for a variable used in a lambda inside the first of multiple loops.

    Closes #6419

•   Fix false positive for unsubscriptable-object in Python 3.8 and below for statements guarded by if TYPE_CHECKING.

    Closes #3979

•   Fix a crash when accessing __code__ and assigning it to a variable.

    Closes #6539

•   Fix a crash when linting a file that passes an integer mode= to open

    Closes #6414

•   Fix false positives for no-name-in-module and import-error for numpy.distutils and pydantic.

    Closes #6497

•   Fix IndexError crash in uninferable_final_decorators method.

    Refs #6531

•   Fix a crash in unnecessary-dict-index-lookup when subscripting an attribute.

    Closes #6557

•   Fix a false positive for undefined-loop-variable when using enumerate().

    Closes #6593

  Full changelog

  What's New in Pylint 2.13.9?

Release date: 2022-05-13

•   Respect ignore configuration options with --recursive=y.

    Closes #6471

•   Fix false positives for no-name-in-module and import-error for numpy.distutils and pydantic.

    Closes #6497

•   Fix IndexError crash in uninferable_final_decorators method.

    Refs #6531

•   Fix a crash in unnecessary-dict-index-lookup when subscripting an attribute.

    Closes #6557

•   Fix a crash when accessing __code__ and assigning it to a variable.

    Closes #6539

•   Fix a false positive for undefined-loop-variable when using enumerate().

    Closes #6593

  What's New in Pylint 2.13.8?

Release date: 2022-05-02

•   Fix a false positive for undefined-loop-variable for a variable used in a lambda inside the first of multiple loops.

    Closes #6419

•   Fix a crash when linting a file that passes an integer mode= to open

    Closes #6414

•   Avoid reporting superfluous-parens on expressions using the is not operator.

    Closes #5930

•   Fix a false positive for undefined-loop-variable when the else of a for loop raises or returns.

    Closes #5971

•   Fix false positive for unused-variable for classes inside functions and where a metaclass is provided via a call.

    Closes #4020

•   Fix false positive for unsubscriptable-object in Python 3.8 and below for statements guarded by if TYPE_CHECKING.

    Closes #3979

  What's New in Pylint 2.13.7?

Release date: 2022-04-20

•   Fix a crash caused by using the new config from 2.14.0 in 2.13.x code.

    Closes #6408

  What's New in Pylint 2.13.6?

Release date: 2022-04-20

•   Fix a crash in the unsupported-membership-test checker when assigning multiple constants to class attributes including __iter__ via unpacking.

    Closes #6366

•   Asterisks are no longer required in Sphinx and Google style parameter documentation for missing-param-doc and are parsed correctly.

    Closes #5815 Closes #5406

•   Fixed a false positive for unused-variable when a builtin specified in --additional-builtins is given a type annotation.

    Closes #6388

•   Fixed an AstroidError in 2.13.0 raised by the duplicate-code checker with ignore-imports or ignore-signatures enabled.

    Closes #6301

  What's New in Pylint 2.13.5?

Release date: 2022-04-06

•   Fix false positive regression in 2.13.0 for used-before-assignment for homonyms between variable assignments in try/except blocks and variables in subscripts in comprehensions.

    Closes #6069 Closes #6136

•   lru-cache-decorating-method has been renamed to cache-max-size-none and will only be emitted when maxsize is None.

    Closes #6180

•   Fix false positive for unused-import when disabling both used-before-assignment and undefined-variable.

    Closes #6089

•   Narrow the scope of the unnecessary-ellipsis checker to: * functions & classes which contain both a docstring and an ellipsis. * A body which contains an ellipsis nodes.Expr node & at least one other statement.

•   Fix false positive for used-before-assignment for assignments taking place via nonlocal declarations after an earlier type annotation.

    Closes #5394

•   Fix crash for redefined-slots-in-subclass when the type of the slot is not a const or a string.

    Closes #6100

•   Only raise not-callable when all the inferred values of a property are not callable.

    Closes #5931

•   Fix a false negative for subclassed-final-class when a set of other messages were disabled.

  What's New in Pylint 2.13.4?

Release date: 2022-03-31

•   Fix false positive regression in 2.13.0 for used-before-assignment for homonyms between variable assignments in try/except blocks and variables in a comprehension's filter.

    Closes #6035

•   Include testing_pylintrc in source and wheel distributions.

    Closes #6028

•   Fix crash in super-init-not-called checker when using ctypes.Union.

    Closes #6027

•   Fix crash for unnecessary-ellipsis checker when an ellipsis is used inside of a container or a lambda expression.

    Closes #6036 Closes #6037 Closes #6048

  What's New in Pylint 2.13.3?

Release date: 2022-03-29

•   Fix false positive for unnecessary-ellipsis when using an ellipsis as a default argument.

    Closes #5973

•   Fix crash involving unbalanced tuple unpacking.

    Closes #5998

•   Fix false positive for 'nonexistent-operator' when repeated '-' are separated (e.g. by parens).

    Closes #5769

  What's New in Pylint 2.13.2?

Release date: 2022-03-27

•   Fix crash when subclassing a namedtuple.

    Closes #5982

•   Fix false positive for superfluous-parens for patterns like "return (a or b) in iterable".

    Closes #5803

•   Fix a false negative regression in 2.13.0 where protected-access was not raised on functions.

    Closes #5989

•   Better error messages in case of crash if pylint can't write the issue template.

    Refs #5987

  What's New in Pylint 2.13.1?

Release date: 2022-03-26

•   Fix a regression in 2.13.0 where used-before-assignment was emitted for the usage of a nonlocal in a try block.

    Closes #5965

•   Avoid emitting raising-bad-type when there is inference ambiguity on the variable being raised.

    Closes #2793

•   Loosen TypeVar default name pattern a bit to allow names with multiple uppercase characters. E.g. HVACModeT or IPAddressT.

    Closes #5981

•   Fixed false positive for unused-argument when a nonlocal name is used in a nested function that is returned without being called by its parent.

    Closes #5187

•   Fix program crash for modified_iterating-list/set/dict when the list/dict/set being iterated through is a function call.

    Closes #5969

•   Don't emit broken-noreturn and broken-collections-callable errors inside if TYPE_CHECKING blocks.

  What's New in Pylint 2.13.0?

Release date: 2022-03-24

•   Add missing dunder methods to unexpected-special-method-signature check.

•   No longer emit no-member in for loops that reference self if the binary operation that started the for loop uses a self that is encapsulated in tuples or lists.

    Refs PyCQA/astroid#1360 Closes #4826

•   Output better error message if unsupported file formats are used with pyreverse.

    Closes #5950

•   Fix pyreverse diagrams type hinting for classmethods and staticmethods.

•   Fix pyreverse diagrams type hinting for methods returning None.

•   Fix matching --notes options that end in a non-word character.

    Closes #5840

•   Updated the position of messages for class and function definitions to no longer cover the complete definition. Only the def or class + the name of the class/function are covered.

    Closes #5466

•

using-f-string-in-unsupported-version and using-final-decorator-in-unsupported-version msgids
    were renamed from W1601 and W1602 to W2601 and W2602. Disabling using these msgids will break. This is done in order to restore consistency with the already existing msgids for apply-builtin and basestring-builtin from the now deleted python 3K+ checker. There is now a check that we're not using existing msgids or symbols from deleted checkers.

    Closes #5729

•   The line numbering for messages related to function arguments is now more accurate. This can require some message disables to be relocated to updated positions.

•   Add --recursive option to allow recursive discovery of all modules and packages in subtree. Running pylint with --recursive=y option will check all discovered .py files and packages found inside subtree of directory provided as parameter to pylint.

    Closes #352

•   Add modified-iterating-list, modified-iterating-dict and modified-iterating-set, emitted when items are added to or removed from respectively a list, dictionary or set being iterated through.

    Closes #5348

•   Fix false-negative for assignment-from-none checker using list.sort() method.

    Closes #5722

•   New extension import-private-name: indicate imports of external private packages and objects (prefixed with _). It can be loaded using load-plugins=pylint.extensions.private_import.

    Closes #5463

•   Fixed crash from arguments-differ and arguments-renamed when methods were defined outside the top level of a class.

    Closes #5648

•   Removed the deprecated check_docs extension. You can use the docparams checker to get the checks previously included in check_docs.

    Closes #5322

•   Added a testutil extra require to the packaging, as gitpython should not be a dependency all the time but is still required to use the primer helper code in pylint.testutil. You can install it with pip install pylint[testutil].

    Closes #5486

•   Reinstated checks from the python3 checker that are still useful for python 3 (eq-without-hash). This is now in the pylint.extensions.eq_without_hash optional extension.

    Closes #5025

•   Fixed an issue where ungrouped-imports could not be disabled without raising useless-suppression.

    Refs #2366

•   Added several checkers to deal with unicode security issues (see Trojan Sources and PEP 672 for details) that also concern the readability of the code. In detail the following checks were added:

•   bad-file-encoding checks that the file is encoded in UTF-8 as suggested by PEP8. UTF-16 and UTF-32 are not supported by Python at the moment. If this ever changes invalid-unicode-codec checks that they aren't used, to allow for backwards compatibility.

•   bidirectional-unicode checks for bidirectional unicode characters that could make code execution different than what the user expects.

•   invalid-character-backspace, invalid-character-carriage-return, invalid-character-sub, invalid-character-esc, invalid-character-zero-width-space and invalid-character-nul to check for possibly harmful unescaped characters.

    Closes #5281

•   Use the tomli package instead of toml to parse .toml files.

    Closes #5885

•   Fix false positive - Allow unpacking of self in a subclass of typing.NamedTuple.

    Closes #5312

•   Fixed false negative unpacking-non-sequence when value is an empty list.

    Closes #5707

•   Better warning messages for useless else or elif when a function returns early.

    Closes #5614

•   Fixed false positive consider-using-dict-comprehension when creating a dict using a list of tuples where key AND value vary depending on the same condition.

    Closes #5588

•   Fixed false positive for global-variable-undefined when global is used with a class name

    Closes #3088

•   Fixed false positive for unused-variable when a nonlocal name is assigned as part of a multi-name assignment.

    Closes #3781

•   Fixed a crash in unspecified-encoding checker when providing None to the mode argument of an open() call.

    Closes #5731

•   Fixed a crash involving a NewType named with an f-string.

    Closes #5770 Ref PyCQA/astroid#1400

•   Improved bad-open-mode message when providing None to the mode argument of an open() call.

    Closes #5733

•   Added lru-cache-decorating-method checker with checks for the use of functools.lru_cache on class methods. This is unrecommended as it creates memory leaks by never letting the instance getting garbage collected.

    Closes #5670

•   Fixed crash with recursion error for inference of class attributes that referenced the class itself.

    Closes #5408 Ref PyCQA/astroid#1392

•   Fixed false positive for unused-argument when a method overridden in a subclass does nothing with the value of a keyword-only argument.

    Closes #5771 Ref PyCQA/astroid#1382

•   The issue template for crashes is now created for crashes which were previously not covered by this mechanism.

    Closes #5668

•

Rewrote checker for non-ascii-name.
    It now ensures __all__ Python names are ASCII and also properly checks the names of imports (non-ascii-module-import) as well as file names (non-ascii-file-name) and emits their respective new warnings.

    Non ASCII characters could be homoglyphs (look alike characters) and hard to enter on a non specialized keyboard. See Confusable Characters in PEP 672

•   When run in parallel mode pylint now pickles the data passed to subprocesses with the dill package. The dill package has therefore been added as a dependency.

•   An astroid issue where symlinks were not being taken into account was fixed

    Closes #1470 Closes #3499 Closes #4302 Closes #4798 Closes #5081

•   Fix a crash in unused-private-member checker when analyzing code using type(self) in bound methods.

    Closes #5569

•   Optimize parsing of long lines when missing-final-newline is enabled.

    Closes #5724

•   Fix false positives for used-before-assignment from using named expressions in a ternary operator test and using that expression as a call argument.

    Closes #5177, #5212

•   Fix false positive for undefined-variable when namedtuple class attributes are used as return annotations.

    Closes #5568

•   Fix false negative for undefined-variable and related variable messages when the same undefined variable is used as a type annotation and is accessed multiple times, or is used as a default argument to a function.

    Closes #5399

•   Pyreverse - add output in mermaidjs format

•   Emit used-before-assignment instead of undefined-variable when attempting to access unused type annotations.

    Closes #5713

•   Added confidence level CONTROL_FLOW for warnings relying on assumptions about control flow.

•   used-before-assignment now considers that assignments in a try block may not have occurred when the except or finally blocks are executed.

    Closes #85, #2615

•   Fixed false negative for used-before-assignment when a conditional or context manager intervened before the try statement that suggested it might fail.

    Closes #4045

•   Fixed false negative for used-before-assignment in finally blocks if an except handler did not define the assignment that might have failed in the try block.

•   Fixed extremely long processing of long lines with comma's.

    Closes #5483

•   Fixed crash on properties and inherited class methods when comparing them for equality against an empty dict.

    Closes #5646

•   Fixed a false positive for assigning-non-slot when the slotted class defined __setattr__.

    Closes #3793

•   Fixed a false positive for invalid-class-object when the object being assigned to the __class__ attribute is uninferable.

•   Fixed false positive for used-before-assignment with self-referential type annotation in conditional statements within class methods.

    Closes #5499

•   Add checker redefined-slots-in-subclass: Emitted when a slot is redefined in a subclass.

    Closes #5617

•   Fixed false positive for global-variable-not-assigned when the del statement is used

    Closes #5333

•   By default, pylint does no longer take files starting with .# into account. Those are considered Emacs file locks. See https://www.gnu.org/software/emacs/manual/html_node/elisp/File-Locks.html. This behavior can be reverted by redefining the ignore-patterns option.

    Closes #367

•   Fixed a false positive for used-before-assignment when a named expression appears as the first value in a container.

    Closes #5112

•   used-before-assignment now assumes that assignments in except blocks may not have occurred and warns accordingly.

    Closes #4761

•   When evaluating statements after an except block, used-before-assignment assumes that assignments in the except blocks took place if the corresponding try block contained a return statement.

    Closes #5500

•   Fixed a false negative for used-before-assignment when some but not all except handlers defined a name relied upon after an except block when the corresponding try block contained a return statement.

    Closes #5524

•   When evaluating statements in the else clause of a loop, used-before-assignment assumes that assignments in the except blocks took place if the except handlers constituted the only ways for the loop to finish without breaking early.

    Closes #5683

•   used-before-assignment now checks names in try blocks.

•   Fixed false positive with used-before-assignment for assignment expressions in lambda statements.

    Closes #5360, #3877

•   Fixed a false positive (affecting unreleased development) for used-before-assignment involving homonyms between filtered comprehensions and assignments in except blocks.

    Closes #5586

•   Fixed crash with slots assignments and annotated assignments.

    Closes #5479

•   Fixed crash on list comprehensions that used type as inner variable name.

    Closes #5461

•   Fixed crash in use-maxsplit-arg checker when providing the sep argument to str.split() by keyword.

    Closes #5737

•   Fix false positive for unused-variable for a comprehension variable matching an outer scope type annotation.

    Closes #5326

•   Fix false negative for undefined-variable for a variable used multiple times in a comprehension matching an unused outer scope type annotation.

    Closes #5654

•   Some files in pylint.testutils were deprecated. In the future imports should be done from the pylint.testutils.functional namespace directly.

•   Fixed false positives for no-value-for-parameter with variadic positional arguments.

    Closes #5416

•   safe_infer no longer makes an inference when given two function definitions with differing numbers of arguments.

    Closes #3675

•   Fix comparison-with-callable false positive for callables that raise, such as typing constants.

    Closes #5557

•   Fixed a crash on __init__ nodes when the attribute was previously uninferable due to a cache limit size. This limit can be hit when the inheritance pattern of a class (and therefore of the __init__ attribute) is very large.

    Closes #5679

•   Fix false positive for used-before-assignment from a class definition nested under a function subclassing a class defined outside the function.

    Closes #4590

•   Fix unnecessary_dict_index_lookup false positive when deleting a dictionary's entry.

    Closes #4716

•   Fix false positive for used-before-assignment when an except handler shares a name with a test in a filtered comprehension.

    Closes #5817

•   Fix crash in unnecessary-dict-index-lookup checker if the output of items() is assigned to a 1-tuple.

    Closes #5504

•   When invoking pylint, epylint, symilar or pyreverse by importing them in a python file you can now pass an argv keyword besides patching sys.argv.

    Closes #5320

•   The PyLinter class will now be initialized with a TextReporter as its reporter if none is provided.

•   Fix super-init-not-called when parent or self is a Protocol

    Closes #4790

•   Fix false positive not-callable with attributes that alias NamedTuple

    Fixes part of #1730

•   Emit redefined-outer-name when a nested except handler shadows an outer one.

    Closes #4434 Closes #5370

•   Fix false positive super-init-not-called for classes that inherit their init from a parent.

    Closes #4941

•   encoding can now be supplied as a positional argument to calls that open files without triggering unspecified-encoding.

    Closes #5638

•   Fatal errors now emit a score of 0.0 regardless of whether the linted module contained any statements

    Closes #5451

•   fatal was added to the variables permitted in score evaluation expressions.

•   The default score evaluation now uses a floor of 0.

    Closes #2399

•   Fix false negative for consider-iterating-dictionary during membership checks encapsulated in iterables or not in checks

    Closes #5323

•   Fixed crash on uninferable decorators on Python 3.6 and 3.7

•   Add checker unnecessary-ellipsis: Emitted when the ellipsis constant is used unnecessarily.

    Closes #5460

•   Disable checker bad-docstring-quotes for Python <= 3.7, because in these versions the line numbers for decorated functions and classes are not reliable which interferes with the checker.

    Closes #3077

•   Fixed incorrect classification of Numpy-style docstring as Google-style docstring for docstrings with property setter documentation. Docstring classification is now based on the highest amount of matched sections instead of the order in which the docstring styles were tried.

•   Fixed detection of arguments-differ when superclass static methods lacked a @staticmethod decorator.

    Closes #5371

•   TypingChecker

•   Added new check broken-noreturn to detect broken uses of typing.NoReturn if py-version is set to Python 3.7.1 or below. https://bugs.python.org/issue34921

•   Added new check broken-collections-callable to detect broken uses of collections.abc.Callable if py-version is set to Python 3.9.1 or below. https://bugs.python.org/issue42965

•   The testutils for unittests now accept end_lineno and end_column. Tests without these will trigger a DeprecationWarning.

•   arguments-differ will no longer complain about method redefinitions with extra parameters that have default values.

    Closes #1556, #5338

•   Fixed false positive unexpected-keyword-arg for decorators.

    Closes #258

•   Importing the deprecated stdlib module xml.etree.cElementTree now emits deprecated_module.

    Closes #5862

•   Disables for deprecated-module and similar warnings for stdlib features deprecated in newer versions of Python no longer raise useless-suppression when linting with older Python interpreters where those features are not yet deprecated.

•   Importing the deprecated stdlib module distutils now emits deprecated_module on Python 3.10+.

•   missing-raises-doc will now check the class hierarchy of the raised exceptions

    def my_function():
      """My function.
      Raises:
        Exception: if something fails
      """
      raise ValueError

    Closes #4955

•   Disable spellchecking of mypy rule names in ignore directives.

    Closes #5929

•   Allow disabling duplicate-code with a disable comment when running through pylint.

    Closes #214

•   Improve invalid-name check for TypeVar names. The accepted pattern can be customized with --typevar-rgx.

    Closes #3401

•   Added new checker typevar-name-missing-variance. Emitted when a covariant or contravariant TypeVar does not end with _co or _contra respectively or when a TypeVar is not either but has a suffix.

•   Allow usage of mccabe 0.7.x release

    Closes #5878

•   Fix unused-private-member false positive when accessing private methods through property.

    Closes #4756

  What's New in Pylint 2.12

From pylint's beginning to pylint 2.14.0 included, we had a changelog that contained all nontrivial changes to Pylint, including changes that were not user facing, i.e. change that might interest you only if you're a developer working on pylint or pylint plugins or an open-source historian.

From pylint 1.6.0 to 2.14.0, on top of the full changelog there was also a summary of (mostly user facing) changes.

  Summary -- Release highlights

In 2.12, we introduced a new option py-version that permits to analyse code for a python version that may differ from your current python interpreter. This does not affect all checkers but permits, for example, to check for python 3.5 code smells (using f-string's) while using pylint with python 3.6. The minimum version to run pylint is now 3.6.2, while the last working version for python 3.6.0 and 3.6.1 was pylint 2.9.3.

On top of fixing a lot of false positives and bugs, we also added new default checks, like use-implicit-booleaness-not-comparison, overridden-final-method, and useless-with-lock. There's also better check for TOML configurations.

Lastly, in addition to the information we already had about start line and start column, we introduced new information about the end line and end column of messages. This will permit to have more precise visual clue in IDE like in pylint for vs-code. The default will stay the same to not break compatibility but it can be retrieved by adding end_line and end_column to the --msg-template option. For better result stick to python 3.8+.

The checker for Yoda conditions is now an extension, you might want to enable it if you were relying on this check. There's also a new extension checker, consider-using-any-or-all that detects for loops that could be replaced by any or all, entirely contributed by @areveny, welcome to the team !

  New checkers

•   Added missing-any-param-doc triggered when a function has neither parameter nor parameter type documentation. Undocumented parameters are now being properly identified. A warning might start to appear unexpectedly if missing-param-doc and missing-type-doc were disabled, as a new message missing-any-param-doc will be emitted instead.

    Closes #3799

  typing.final

•   Added overridden-final-method: Emitted when a method which is annotated with typing.final is overridden

•   Added subclassed-final-class: Emitted when a class which is annotated with typing.final is subclassed

    Closes #3197

•   Created new UnsupportedVersionChecker checker class that includes checks for features not supported by all versions indicated by a py-version.

•   Added using-f-string-in-unsupported-version checker. Issued when py-version is set to a version that does not support f-strings (< 3.6)

•   Added new checker use-implicit-booleaness-not-comparison: Emitted when collection literal comparison is being used to check for emptiness.

    Closes #4774

•   Added using-final-decorator-in-unsupported-version checker. Issued when py-version is set to a version that does not support typing.final (< 3.8)

•   Added new checker useless-with-lock to find incorrect usage of with statement and threading module locks. Emitted when with threading.Lock(): is used instead of with lock_instance:.

    Closes #5208

•   A new bad-configuration-section checker was added that will emit for misplaced option in pylint's top level namespace for toml configuration. Top-level dictionaries or option defined in the wrong section will still silently not be taken into account, which is tracked in a follow-up issue.

    Follow-up in #5259

•   MessageTest of the unittest testutil now requires the confidence attribute to match the expected value. If none is provided it is set to UNDEFINED.

•   add_message of the unittest testutil now actually handles the col_offset parameter and allows it to be checked against actual output in a test.

  Extensions

•   Added an optional extension consider-using-any-or-all: Emitted when a for loop only produces a boolean and could be replaced by any or all using a generator. Also suggests a suitable any/all statement if it is concise.

    Closes #5008

•   Moved misplaced-comparison-constant to its own extension comparison_placement. This checker was opinionated and now no longer a default. It can be reactived by adding pylint.extensions.comparison_placement to load-plugins in your config.

    Closes #1064

  Other Changes

•   Fix install graphiz message which isn't needed for puml output format.

•   pylint no longer crashes when checking assignment expressions within if-statements

    Closes #5178

•   Added configuration option exclude-too-few-public-methods to allow excluding classes from the min-public-methods checker.

    Closes #3370

•   Fix accept-no-yields-doc and accept-no-return-doc not allowing missing yield or return documentation when a docstring is partially correct

    Closes #5223

•   Fix simplify-boolean-expression when condition can be inferred as False.

    Closes #5200

•   Fix exception when pyreverse parses property function of a class.

•   Improve and flatten unused-wildcard-import message

    Closes #3859

•   In length checker, len-as-condition has been renamed as use-implicit-booleaness-not-len in order to be consistent with use-implicit-booleaness-not-comparison.

•   Fixed protected-access for accessing of attributes and methods of inner classes

    Closes #3066

•   Update literal-comparison` checker to ignore tuple literals

    Closes #3031

•   The functional testutils now accept end_lineno and end_column. Expected output files without these will trigger a DeprecationWarning. Expected output files can be easily updated with the python tests/test_functional.py --update-functional-output command.

•   The functional testutils now correctly check the distinction between HIGH and UNDEFINED confidence. Expected output files without defined confidence levels will now trigger a DeprecationWarning. Expected output files can be easily updated with the python tests/test_functional.py --update-functional-output command.

•   The functional test runner now supports the option min_pyver_end_position to control on which python versions the end_lineno and end_column attributes should be checked. The default value is 3.8.

•   undefined-variable now correctly flags variables which only receive a type annotations and never get assigned a value

    Closes #5140

•   undefined-variable now correctly considers the line numbering and order of classes used in metaclass declarations

    Closes #4031

•   used-before-assignment now correctly considers references to classes as type annotation or default values in first-level methods

    Closes #3771

•   undefined-variable and unused-variable now correctly trigger for assignment expressions in functions defaults

    Refs #3688

•   self-cls-assignment now also considers tuple assignment

•   undefined-variable now correctly triggers for assignment expressions in if ... else statements This includes a basic form of control flow inference for if ... else statements using constant boolean values

    Closes #3688

•   Fix crash for unused-private-member when checking private members on __class__

    Closes #5261

•   Fix double emitting of not-callable on inferable properties

    Closes #4426

•   Support configuring mixin class pattern via mixin-class-rgx

•   Normalize the input to the ignore-paths option to allow both Posix and Windows paths

    Closes #5194

•   missing-param-doc now correctly parses asterisks for variable length and keyword parameters

    Closes #3733

•   missing-param-doc now correctly handles Numpy parameter documentation without explicit typing

    Closes #5222

•   The --jobs parameter now falls back to 1 if the host operating system does not have functioning shared semaphore implementation.

    Closes #5216

•   Crashes when a list is encountered in a toml configuration do not happen anymore.

    Closes #4580

•   Fix crash for protected-access on (outer) class traversal

•   Fix useless-super-delegation false positive when default keyword argument is a variable.

•   Make yn validator case insensitive, to allow for True and False in config files.

•   The last version compatible with python '3.6.0' and '3.6.1' is pylint '2.9.3'. We did not realize that when adding incompatible typing at the time, and all versions since are broken for this interpreter. 2.12.0 meta-information will permit to download pylint on those interpreters but the installation will fail and tell you to install '2.9.3' instead. pylint 2.12.1 will require python >= 3.6.2.

    Closes #5171 Follow-up in #5065

•   Added the --enable-all-extensions command line option. It will load all available extensions which can be listed by running --list-extensions

•   It is now recommended to do pylint development on Python 3.8 or higher. This allows using the latest ast parser.

•   All standard jobs in the pylint CI now run on Python 3.8 by default. We still support python 3.6 and 3.7 and run tests for those interpreters.

•   Fix crash on open() calls when the mode argument is not a simple string.

    Fixes part of #5321

•   Add ability to add end_line and end_column to the --msg-template option. With the standard TextReporter this will add the line and column number of the end of a node to the output of Pylint. If these numbers are unknown, they are represented by an empty string.

•   Introduced primer tests and a configuration tests framework. The helper classes available in pylint/testutil/ are still unstable and might be modified in the near future.

    Closes #4412 #5287

•   Add endLine and endColumn keys to output of JSONReporter.

    Closes #5380

•   Fix false negative for consider-iterating-dictionary during membership checks encapsulated in iterables or not in checks

    Closes #5323

  Full changelog

  What's New in Pylint 2.12.2?

Release date: 2021-11-25

•   Fixed a false positive for unused-import where everything was not analyzed properly inside typing guards.

•   Fixed a false-positive regression for used-before-assignment for typed variables in the body of class methods that reference the same class

    Closes #5342

•   Specified that the ignore-paths option considers "" to represent a windows directory delimiter instead of a regular expression escape character.

•   Fixed a crash with the ignore-paths option when invoking the option via the command line.

    Closes #5437

•   Fixed handling of Sphinx-style parameter docstrings with asterisks. These should be escaped with by prepending a "".

    Closes #5406

•   Add endLine and endColumn keys to output of JSONReporter.

    Closes #5380

•   Fixed handling of Google-style parameter specifications where descriptions are on the line following the parameter name. These were generating false positives for missing-param-doc.

    Closes #5452

•   Fix false negative for consider-iterating-dictionary during membership checks encapsulated in iterables or not in checks

    Closes #5323

•   unused-import now check all ancestors for typing guards

    Closes #5316

  What's New in Pylint 2.12.1?

Release date: 2021-11-25

•   Require Python 3.6.2 to run pylint.

    Closes #5065

  What's New in Pylint 2.12.0?

Release date: 2021-11-24

•   Upgrade astroid to 2.9.0

    Closes #4982

•   Add ability to add end_line and end_column to the --msg-template option. With the standard TextReporter this will add the line and column number of the end of a node to the output of Pylint. If these numbers are unknown, they are represented by an empty string.

•   Introduced primer tests and a configuration tests framework. The helper classes available in pylint/testutil/ are still unstable and might be modified in the near future.

    Closes #4412 #5287

•   Fix install graphiz message which isn't needed for puml output format.

•   MessageTest of the unittest testutil now requires the confidence attribute to match the expected value. If none is provided it is set to UNDEFINED.

•   add_message of the unittest testutil now actually handles the col_offset parameter and allows it to be checked against actual output in a test.

•   Fix a crash in the check_elif extensions where an undetected if in a comprehension with an if statement within a f-string resulted in an out of range error. The checker no longer relies on counting if statements anymore and uses known if statements locations instead. It should not crash on badly parsed if statements anymore.

•   Fix simplify-boolean-expression when condition can be inferred as False.

    Closes #5200

•   Fix exception when pyreverse parses property function of a class.

•   The functional testutils now accept end_lineno and end_column. Expected output files without these will trigger a DeprecationWarning. Expected output files can be easily updated with the python tests/test_functional.py --update-functional-output command.

•   The functional testutils now correctly check the distinction between HIGH and UNDEFINED confidence. Expected output files without defined confidence levels will now trigger a DeprecationWarning. Expected output files can be easily updated with the python tests/test_functional.py --update-functional-output command.

•   The functional test runner now supports the option min_pyver_end_position to control on which python versions the end_lineno and end_column attributes should be checked. The default value is 3.8.

•   Fix accept-no-yields-doc and accept-no-return-doc not allowing missing yield or return documentation when a docstring is partially correct

    Closes #5223

•   Add an optional extension consider-using-any-or-all : Emitted when a for loop only produces a boolean and could be replaced by any or all using a generator. Also suggests a suitable any or all statement.

    Closes #5008

•   Properly identify parameters with no documentation and add new message called missing-any-param-doc

    Closes #3799

•   Add checkers overridden-final-method & subclassed-final-class

    Closes #3197

•   Fixed protected-access for accessing of attributes and methods of inner classes

    Closes #3066

•   Added support for ModuleNotFoundError (import-error and no-name-in-module). ModuleNotFoundError inherits from ImportError and was added in Python 3.6

•   undefined-variable now correctly flags variables which only receive a type annotations and never get assigned a value

    Closes #5140

•   undefined-variable now correctly considers the line numbering and order of classes used in metaclass declarations

    Closes #4031

•   used-before-assignment now correctly considers references to classes as type annotation or default values in first-level methods

    Closes #3771

•   undefined-variable and unused-variable now correctly trigger for assignment expressions in functions defaults

    Refs #3688

•   undefined-variable now correctly triggers for assignment expressions in if ... else statements This includes a basic form of control flow inference for if ... else statements using constant boolean values

    Closes #3688

•   Added the --enable-all-extensions command line option. It will load all available extensions which can be listed by running --list-extensions

•   Fix bug with importing namespace packages with relative imports

    Closes #2967 and #5131

•   Improve and flatten unused-wildcard-import message

    Closes #3859

•   In length checker, len-as-condition has been renamed as use-implicit-booleaness-not-len in order to be consistent with use-implicit-booleaness-not-comparison.

•   Created new UnsupportedVersionChecker checker class that includes checks for features not supported by all versions indicated by a py-version.

•   Added using-f-string-in-unsupported-version checker. Issued when py-version is set to a version that does not support f-strings (< 3.6)

•   Fix useless-super-delegation false positive when default keyword argument is a variable.

•   Properly emit duplicate-key when Enum members are duplicate dictionary keys

    Closes #5150

•   Use py-version setting for alternative union syntax check (PEP 604), instead of the Python interpreter version.

•   Subclasses of dict are regarded as reversible by the bad-reversed-sequence checker (Python 3.8 onwards).

    Closes #4981

•   Support configuring mixin class pattern via mixin-class-rgx

•   Added new checker use-implicit-booleaness-not-comparison: Emitted when collection literal comparison is being used to check for emptiness.

    Closes #4774

•   missing-param-doc now correctly parses asterisks for variable length and keyword parameters

    Closes #3733

•   missing-param-doc now correctly handles Numpy parameter documentation without explicit typing

    Closes #5222

•   pylint no longer crashes when checking assignment expressions within if-statements

    Closes #5178

•   Update literal-comparison` checker to ignore tuple literals

    Closes #3031

•   Normalize the input to the ignore-paths option to allow both Posix and Windows paths

    Closes #5194

•   Fix double emitting of not-callable on inferable properties

    Closes #4426

•   self-cls-assignment now also considers tuple assignment

•   Fix missing-function-docstring not being able to check __init__ and other magic methods even if the no-docstring-rgx setting was set to do so

•   Added using-final-decorator-in-unsupported-version checker. Issued when py-version is set to a version that does not support typing.final (< 3.8)

•   Added configuration option exclude-too-few-public-methods to allow excluding classes from the min-public-methods checker.

    Closes #3370

•   The --jobs parameter now fallbacks to 1 if the host operating system does not have functioning shared semaphore implementation.

    Closes #5216

•   Fix crash for unused-private-member when checking private members on __class__

    Closes #5261

•   Crashes when a list is encountered in a toml configuration do not happen anymore.

    Closes #4580

•   Moved misplaced-comparison-constant to its own extension comparison_placement. This checker was opinionated and now no longer a default. It can be reactived by adding pylint.extensions.comparison_placement to load-plugins in your config.

    Closes #1064

•   A new bad-configuration-section checker was added that will emit for misplaced option in pylint's top level namespace for toml configuration. Top-level dictionaries or option defined in the wrong section will still silently not be taken into account, which is tracked in a follow-up issue.

    Follow-up in #5259

•   Fix crash for protected-access on (outer) class traversal

•   Added new checker useless-with-lock to find incorrect usage of with statement and threading module locks. Emitted when with threading.Lock(): is used instead of with lock_instance:.

    Closes #5208

•   Make yn validator case insensitive, to allow for True and False in config files.

•   Fix crash on open() calls when the mode argument is not a simple string.

    Fixes part of #5321

•   Inheriting from a class that implements __class_getitem__ no longer raises inherit-non-class.

•   Pyreverse - Add the project root directory to sys.path

    Closes #2479

•   Don't emit consider-using-f-string if py-version is set to Python < 3.6. f-strings were added in Python 3.6

    Closes #5019

•   Fix regression for unspecified-encoding with pathlib.Path.read_text()

    Closes #5029

•   Don't emit consider-using-f-string if the variables to be interpolated include a backslash

•   Fixed false positive for cell-var-from-loop when variable is used as the default value for a keyword-only parameter.

    Closes #5012

•   Fix false-positive undefined-variable with Lambda, IfExp, and assignment expression.

•   Fix false-positive useless-suppression for wrong-import-order

    Closes #2366

•   Fixed toml dependency issue

    Closes #5066

•   Fix false-positive useless-suppression for line-too-long

    Closes #4212

•   Fixed invalid-name not checking parameters of overwritten base object methods

    Closes #3614

•   Fixed crash in consider-using-f-string if format is not called

    Closes #5058

•   Fix crash with AssignAttr in if TYPE_CHECKING blocks.

    Closes #5111

•   Improve node information for invalid-name on function argument.

•   Prevent return type checkers being called on functions with ellipses as body

    Closes #4736

•   Add is_sys_guard and is_typing_guard helper functions from astroid to pylint.checkers.utils.

•   Fix regression on ClassDef inference

    Closes #5030 Closes #5036

•   Fix regression on Compare node inference

    Closes #5048

•   Fix false-positive isinstance-second-argument-not-valid-type with typing.Callable.

    Closes #3507 Closes #5087

•   It is now recommended to do pylint development on Python 3.8 or higher. This allows using the latest ast parser.

•   All standard jobs in the pylint CI now run on Python 3.8 by default. We still support python 3.6 and 3.7 and run tests for those interpreters.

•   TypingChecker

•   Fix false-negative for deprecated-typing-alias and consider-using-alias with typing.Type + typing.Callable.

  What's New in Pylint 2.11

From pylint's beginning to pylint 2.14.0 included, we had a changelog that contained all nontrivial changes to Pylint, including changes that were not user facing, i.e. change that might interest you only if you're a developer working on pylint or pylint plugins or an open-source historian.

From pylint 1.6.0 to 2.14.0, on top of the full changelog there was also a summary of (mostly user facing) changes.

  Summary -- Release highlights

In 2.11, we added a new default checker to advise using f-string as it's the most efficient way of formatting strings right now. You can use pyupgrade or flynt to migrate your old % and format() automatically.

We added a new extension SetMembershipChecker that will advise the use of set for membership test, as it's more performant than lists or tuples. The CodeStyleChecker also got some love, check it out if you're not already using it.

We fixed some long standing bugs, false positives, or false negatives and we added small quality of life options like min-similarity-lines that disable the duplication check when set to 0.

Under the hood the code for both pylint and astroid is progressively more typed, which could be helpful to you if you're using them as libraries. In order for this new typing to make more sense and stay simple, we deprecated some functions or type that will be removed in the next major version. This is an ongoing effort.

The future possible-forgotten-f-prefix check still had too much false positives, and is delayed again. Check the possible-forgotten-f-prefix issue if you want to provide knowledge or use case :)

  New checkers

•   Added consider-using-f-string: Emitted when .format() or '%' is being used to format a string.

    Closes #3592

  Removed checkers

•   The python3 porting mode checker and it's py3k option were removed. You can still find it in older pylint versions.

  Extensions

•   Added new extension SetMembershipChecker with use-set-for-membership check: Emitted when using an in-place defined list or tuple to do a membership test. sets are better optimized for that.

    Closes #4776

  CodeStyleChecker

•   Added consider-using-assignment-expr: Emitted when an assignment is directly followed by an if statement and both can be combined by using an assignment expression :=. Requires Python 3.8

    Closes #4862

  Other Changes

•   Added py-version config key (if [MAIN] section). Used for version dependent checks. Will default to whatever Python version pylint is executed with.

•   The invalid-name message is now more detailed when using multiple naming style regexes.

•   Fix false positive for consider-using-with if a context manager is assigned to a variable in different paths of control flow (e. g. if-else clause).

    Closes #4751

•   Fix false positive for function-redefined for simple type annotations

    Closes #4936

•   Fix false positive for protected-access if a protected member is used in type hints of function definitions

•   Fix false positive dict-iter-missing-items for dictionaries only using tuples as keys

    Closes #3282

•   The unspecified-encoding checker now also checks calls to pathlib.Path().read_text() and pathlib.Path().write_text()

    Closes #4945

•   Fix false positive superfluous-parens for tuples created with inner tuples

    Closes #4907

•   Fix false positive unused-private-member for accessing attributes in a class using cls

    Closes #4849

•   Extended consider-using-in check to work for attribute access.

•   Setting min-similarity-lines to 0 now makes the similarty checker stop checking for duplicate code

    Closes #4901

•   Fix a bug where pylint complained if the cache's parent directory does not exist

    Closes #4900

•   The global-variable-not-assigned checker now catches global variables that are never reassigned in a local scope and catches (reassigned) functions

    Closes #1375 Closes #330

•   The consider-iterating-dictionary checker now also considers membership checks

    Closes #4069

  Full changelog

  What's New in Pylint 2.11.1?

Release date: 2021-09-16

•   unspecified-encoding now checks the encoding of pathlib.Path() correctly

    Closes #5017

  What's New in Pylint 2.11.0?

Release date: 2021-09-16

•   The python3 porting mode checker and it's py3k option were removed. You can still find it in older pylint versions.

•   raising-bad-type is now properly emitted when raising a string

•   Added new extension SetMembershipChecker with use-set-for-membership check: Emitted when using an in-place defined list or tuple to do a membership test. sets are better optimized for that.

    Closes #4776

•   Added py-version config key (if [MASTER] section). Used for version dependent checks. Will default to whatever Python version pylint is executed with.

•   CodeStyleChecker: Added consider-using-assignment-expr: Emitted when an assignment is directly followed by an if statement and both can be combined by using an assignment expression :=. Requires Python 3.8

    Closes #4862

•   Added consider-using-f-string: Emitted when .format() or '%' is being used to format a string.

    Closes #3592

•   Fix false positive for consider-using-with if a context manager is assigned to a variable in different paths of control flow (e. g. if-else clause).

    Closes #4751

•   https is now preferred in the documentation and http://pylint.pycqa.org correctly redirect to https://pylint.pycqa.org

    Closes #3802

•   Fix false positive for function-redefined for simple type annotations

    Closes #4936

•   Fix false positive for protected-access if a protected member is used in type hints of function definitions

•   Fix false positive dict-iter-missing-items for dictionaries only using tuples as keys

    Closes #3282

•   The unspecified-encoding checker now also checks calls to pathlib.Path().read_text() and pathlib.Path().write_text()

    Closes #4945

•   Fix false positive superfluous-parens for tuples created with inner tuples

    Closes #4907

•   Fix false positive unused-private-member for accessing attributes in a class using cls

    Closes #4849

•   Fix false positive unused-private-member for private staticmethods accessed in classmethods.

    Closes #4849

•   Extended consider-using-in check to work for attribute access.

•   Setting min-similarity-lines to 0 now makes the similarty checker stop checking for duplicate code

    Closes #4901

•   Fix a bug where pylint complained if the cache's parent directory does not exist

    Closes #4900

•   The global-variable-not-assigned checker now catches global variables that are never reassigned in a local scope and catches (reassigned) functions

    Closes #1375 Closes #330

•   Fix false positives for invalid-all-format that are lists or tuples at runtime

    Closes #4711

•   Fix no-self-use and docparams extension for async functions and methods.

•   Add documentation for pyreverse and symilar

    Closes #4616

•   Non symbolic messages with the wrong capitalisation now correctly trigger use-symbolic-message-instead

    Closes #5000

•   The consider-iterating-dictionary checker now also considers membership checks

    Closes #4069

•   The invalid-name message is now more detailed when using multiple naming style regexes.

  What's New In Pylint 2.10

From pylint's beginning to pylint 2.14.0 included, we had a changelog that contained all nontrivial changes to Pylint, including changes that were not user facing, i.e. change that might interest you only if you're a developer working on pylint or pylint plugins or an open-source historian.

From pylint 1.6.0 to 2.14.0, on top of the full changelog there was also a summary of (mostly user facing) changes.

  Summary -- Release highlights

In 2.10, we added several new default check, like unspecified-encoding, forgotten-debug-statement or use-dict-literal. There's also a few opinionated optional one. You can now forbid while loop or profess your exclusive love of ternary expressions publicly. We promise you hours of arguing fun with your whole team if you add those to your configuration.

We've also fixed some long standing bugs, false positives, or missing options like ignore-signature that will now work on inner function's signatures.

A new option to disable the next line, disable-next, has been added. It's also possible to export colored diagrams, and plantuml diagram using pyreverse. PYLINT_HOME is now XDG_CACHE_HOME if not set.

The performance of the similarity checker has been improved, as well as several small performance fixes.

We're going to continue working on improving performance during 2.11. We're also going to finalize a new possible-forgotten-f-prefix check that had too much false positives at release time. Check the possible-forgotten-f-prefix issue if you want to provide knowledge or use case :)

  New checkers

•   Added unspecified-encoding: Emitted when open() is called without specifying an encoding

    Closes #3826

•   Added use-list-literal: Emitted when list() is called with no arguments instead of using []

    Closes #4365

•   Added use-dict-literal: Emitted when dict() is called with no arguments instead of using {}

    Closes #4365

•   Added forgotten-debug-statement: Emitted when breakpoint, pdb.set_trace or sys.breakpointhook calls are found

    Closes #3692

•   Added use-sequence-for-iteration: Emitted when iterating over an in-place defined set.

•   Added format-string-without-interpolation checker: Emitted when formatting is applied to a string without any variables to be replaced

    Closes #4042

•   Added redundant-u-string-prefix checker: Emitted when the u prefix is added to a string

    Closes #4102

  Extensions

•   CodeStyleChecker

•   Limit consider-using-tuple to be emitted only for in-place defined lists.

•   Emit consider-using-tuple even if list contains a starred expression.

•   Added optional extension consider-ternary-expression: Emitted whenever a variable is assigned in both branches of an if/else block.

    Closes # 4366

•   Added optional extension while-used: Emitted whenever a while loop is used.

    Closes # 4367

  Other Changes

•   pyreverse now permit to produce colored generated diagram by using the colorized option.

•   Pyreverse - add output in PlantUML format

•   consider-using-with is no longer triggered if a context manager is returned from a function.

•   pylint does not crash with a traceback anymore when a file is problematic. It creates a template text file for opening an issue on the bug tracker instead. The linting can go on for other non problematic files instead of being impossible.

•   Pyreverse - Show class has-a relationships inferred from type-hints

•   Performance of the Similarity checker has been improved.

•   Added time.clock to deprecated functions/methods for python 3.3

•   Added ignored-parents option to the design checker to ignore specific classes from the too-many-ancestors check (R0901).

•   Don't emit no-member error if guarded behind if statement.

    Refs #1162 Closes #1990 Closes #4168

•   Fix false positives for superfluous-parens with walrus operator, ternary operator and inside list comprehension.

    Closes #2818 Closes #3249 Closes #3608 Closes #4346

•   Refactor of --list-msgs & --list-msgs-enabled: both options now show whether messages are emittable with the current interpreter.

    Closes #4778

•   Fix false negative for used-before-assignment when the variable is assigned in an exception handler, but used outside of the handler.

    Closes #626

•   Added disable-next option: allows using # pylint: disable-next=msgid to disable a message for the following line

    Closes #1682

•   Fixed cell-var-from-loop checker: handle cell variables in comprehensions within functions, and function default argument expressions. Also handle basic variable shadowing.

    Closes #2846 Closes #3107

•   Fixed bug with cell-var-from-loop checker: it no longer has false negatives when both unused-variable and used-before-assignment are disabled.

•   Class methods' signatures are now ignored the same way as functions' with similarities "ignore-signatures" option enabled

    Closes #4653

  Full changelog

  What's New in Pylint 2.10.2?

Release date: 2021-08-21

•   We now use platformdirs instead of appdirs since the latter is not maintained.

    Closes #4886

•   Fix a crash in the checker raising shallow-copy-environ when failing to infer on copy.copy

    Closes #4891

  What's New in Pylint 2.10.1?

Release date: 2021-08-20

•   pylint does not crash when PYLINT_HOME does not exist.

    Closes #4883

  What's New in Pylint 2.10.0?

Release date: 2021-08-20

•   pyreverse: add option to produce colored output.

    Closes #4488

•   pyreverse: add output in PlantUML format.

    Closes #4498

•   consider-using-with is no longer triggered if a context manager is returned from a function.

    Closes #4748

•   pylint does not crash with a traceback anymore when a file is problematic. It creates a template text file for opening an issue on the bug tracker instead. The linting can go on for other non problematic files instead of being impossible.

•   pyreverse: Show class has-a relationships inferred from the type-hint

    Closes #4744

•   Fixed a crash when importing beyond the top level package during import-error message creation

    Closes #4775

•   Added ignored-parents option to the design checker to ignore specific classes from the too-many-ancestors check (R0901).

    Fixes part of #3057

•   Added unspecified-encoding: Emitted when open() is called without specifying an encoding

    Closes #3826

•   Improved the Similarity checker performance. Fix issue with --min-similarity-lines used with --jobs.

    Closes #4120 Closes #4118

•   Don't emit no-member error if guarded behind if statement.

    Refs #1162 Closes #1990 Closes #4168

•   The default for PYLINTHOME is now the standard XDG_CACHE_HOME, and pylint now uses appdirs.

    Closes #3878

•   Added use-list-literal: Emitted when list() is called with no arguments instead of using []

    Closes #4365

•   Added use-dict-literal: Emitted when dict() is called with no arguments instead of using {}

    Closes #4365

•   Added optional extension consider-ternary-expression: Emitted whenever a variable is assigned in both branches of an if/else block.

    Closes # 4366

•   Added optional extension while-used: Emitted whenever a while loop is used.

    Closes # 4367

•   Added forgotten-debug-statement: Emitted when breakpoint, pdb.set_trace or sys.breakpointhook calls are found

    Closes #3692

•   Fix false-positive of unused-private-member when using nested functions in a class

    Closes #4673

•   Fix crash for unused-private-member that occurred with nested attributes.

    Closes #4755

•   Fix a false positive for unused-private-member with class names

    Closes #4681

•   Fix false positives for superfluous-parens with walrus operator, ternary operator and inside list comprehension.

    Closes #2818 Closes #3249 Closes #3608 Closes #4346

•   Added format-string-without-interpolation checker: Emitted when formatting is applied to a string without any variables to be replaced

    Closes #4042

•   Refactor of --list-msgs & --list-msgs-enabled: both options now show whether messages are emittable with the current interpreter.

    Closes #4778

•   Fix false negative for used-before-assignment when the variable is assigned in an exception handler, but used outside of the handler.

    Closes #626

•   Added disable-next option: allows using # pylint: disable-next=msgid to disable a message for the following line

    Closes #1682

•   Added redundant-u-string-prefix checker: Emitted when the u prefix is added to a string

    Closes #4102

•   Fixed cell-var-from-loop checker: handle cell variables in comprehensions within functions, and function default argument expressions. Also handle basic variable shadowing.

    Closes #2846 Closes #3107

•   Fixed bug with cell-var-from-loop checker: it no longer has false negatives when both unused-variable and used-before-assignment are disabled.

•   Fix false positive for invalid-all-format if the list or tuple builtin functions are used

    Closes #4711

•   Config files can now contain environment variables

    Closes #3839

•   Fix false-positive used-before-assignment with an assignment expression in a Return node

    Closes #4828

•   Added use-sequence-for-iteration: Emitted when iterating over an in-place defined set.

•   CodeStyleChecker

•   Limit consider-using-tuple to be emitted only for in-place defined lists.

•   Emit consider-using-tuple even if list contains a starred expression.

•   Ignore decorators lines by similarities checker when ignore signatures flag enabled

    Closes #4839

•   Allow true and false values in pylintrc for better compatibility with toml config.

•   Class methods' signatures are ignored the same way as functions' with similarities "ignore-signatures" option enabled

    Closes #4653

•   Improve performance when inferring Call nodes, by utilizing caching.

•   Improve error message for invalid-metaclass when the node is an Instance.

  What's New In Pylint 2.9

From pylint's beginning to pylint 2.14.0 included, we had a changelog that contained all nontrivial changes to Pylint, including changes that were not user facing, i.e. change that might interest you only if you're a developer working on pylint or pylint plugins or an open-source historian.

From pylint 1.6.0 to 2.14.0, on top of the full changelog there was also a summary of (mostly user facing) changes.

  Summary -- Release highlights

Pylint is now compatible with python 3.10.

A lot of new checks have been added, some non-opinionated performance warnings like use-maxsplit-arg, some consensual style warnings like unnecessary-dict-index-lookup or new deprecation checks.

We're aiming to reduce pylint noise for first time users and making some new checks optional is a step in that direction. In order to do that we created an optional code style checker that can be loaded using pylint.extensions.code_style with the load-plugins options. More than ever, if as a veteran you want the most checks you can possibly get, you should check the list of pylint extensions..

  New checkers

•   deprecated-decorator: Emitted when deprecated decorator is used.

•   consider-using-dict-items: Emitted when iterating over dictionary keys and then indexing the same dictionary with the key within loop body.

•   use-maxsplit-arg: Emitted either when accessing only the first or last element of str.split().

•   An ignore_signatures option has been added to the similarity checker. It will permits to reduce false positives when multiple functions have the same parameters.

•   unnecessary-dict-index-lookup: Emitted when iterating over dictionary items (key-value pairs) and accessing the value by index lookup.

•   consider-using-from-import: Emitted when a submodule/member of a package is imported and aliased with the same name.

•   New checker unused-private-member: Emitted when a private member (i.e., starts with __) of a class is defined but not used.

•   New checker invalid-class-object: Emitted when a non-class is assigned to a __class__ attribute.

•   invalid-all-format: Emitted when __all__ has an invalid format, i.e. isn't a tuple or list.

•   New checker await-outside-async: Emitted when await is used outside an async function.

•   Add new extension CodeStyleChecker. It includes checkers that can improve code consistency. As such they don't necessarily provide a performance benefit and are often times opinionated.

•   consider-using-tuple: Emitted when an in-place defined list or set can be replaced by a tuple.

•   consider-using-namedtuple-or-dataclass: Emitted when dictionary values can be replaced by namedtuples or dataclass instances.

  Other Changes

•   Fix false-positive consider-using-with (R1732) if a ternary conditional is used together with with

•   Fix false-positive consider-using-with (R1732) if contextlib.ExitStack takes care of calling the __exit__ method

•   Add type annotations to pyreverse dot files

•   Pylint's tags are now the standard form vX.Y.Z and not pylint-X.Y.Z anymore.

•   Fix false-positive too-many-ancestors when inheriting from builtin classes, especially from the collections.abc module

•   The output messages for arguments-differ error message have been customized based on the different error cases.

•   New option --fail-on=<msg ids> to return non-zero exit codes regardless of fail-under value.

•   A new error called arguments-renamed has been created, which identifies any changes at the parameter names of overridden functions. It aims to separate the functionality of arguments-differ.

•   Fix incompatibility with Python 3.6.0 caused by typing.Counter and typing.NoReturn usage

•   Allow comma-separated list in output-format and separate output files for each specified format. Each output file can be defined after a semicolon for example : --output-format=json:myfile.json,colorized

•   The using-constant-test checker now detects constant tests consisting of list literals like [] and [1, 2, 3].

•   ignore-paths configuration directive has been added. Defined regex patterns are matched against file path.

•   Added handling of floating point values when parsing configuration from pyproject.toml

•   Fix false positive useless-type-doc on ignored argument using pylint.extensions.docparams when a function was typed using pep484 but not inside the docstring.

•   Fix missing support for detecting deprecated aliases to existing functions/methods. functions/methods.

•   Added various deprecated functions/methods for python 3.10, 3.7, 3.6 and 3.3

•   No longer emit consider-using-with for ThreadPoolExecutor and ProcessPoolExecutor as they have legitimate use cases without a with block.

•   Fix crash if a callable returning a context manager was assigned to a list or dict item

  Full changelog

  What's New in Pylint 2.9.6?

Release date: 2021-07-28

•   Fix a false positive undefined-variable when variable name in decoration matches function argument

    Closes #3791

  What's New in Pylint 2.9.5?

Release date: 2021-07-21

•   Fix a crash when there would be a 'TypeError object does not support item assignment' in the code we parse.

    Closes #4439

•   Fix crash if a callable returning a context manager was assigned to a list or dict item

    Closes #4732

•   Fix a crash when an AttributeInferenceError was not handled properly when failing to infer the real name of an import in astroid.

    Closes #4692

  What's New in Pylint 2.9.4?

Release date: 2021-07-20

•   Added time.clock to deprecated functions/methods for python 3.3

•   Fix bug in which --fail-on can return a zero exit code even when the specified issue is present

    Closes #4296 Closes #3363

•   Fix hard failure when handling missing attribute in a class with duplicated bases

    Closes #4687

•   Fix false-positive consider-using-with (R1732) if a ternary conditional is used together with with

    Closes #4676

•   Fix false-positive deprecated-module when relative import uses deprecated module name.

    Closes #4629

•   Fix false-positive consider-using-with (R1732) if contextlib.ExitStack takes care of calling the __exit__ method

    Closes #4654

•   Fix a false positive for unused-private-member when mutating a private attribute with cls

    Closes #4657

•   Fix ignored empty functions by similarities checker with "ignore-signatures" option enabled

    Closes #4652

•   Fix false-positive of use-maxsplit-arg when index is incremented in a loop

    Closes #4664

•   Don't emit cyclic-import message if import is guarded by typing.TYPE_CHECKING.

    Closes #3525

•   Fix false-positive not-callable with alternative TypedDict syntax

    Closes #4715

•   Clarify documentation for consider-using-from-import

•   Don't emit unreachable warning for empty generator functions

    Closes #4698

•   Don't emit import-error, no-name-in-module, and ungrouped-imports for imports guarded by sys.version_info or typing.TYPE_CHECKING.

    Closes #3285 Closes #3382

•   Fix invalid-overridden-method with nested property

    Closes #4368

•   Fix false-positive of unused-private-member when using __new__ in a class

    Closes #4668

•   No longer emit consider-using-with for ThreadPoolExecutor and ProcessPoolExecutor as they have legitimate use cases without a with block.

    Closes #4689

•   Fix crash when inferring variables assigned in match patterns

    Closes #4685

•   Fix a crash when a StopIteration was raised when inferring a faulty function in a context manager.

    Closes #4723

  What's New in Pylint 2.9.3?

Release date: 2021-07-01

•   Fix a crash that happened when analysing empty function with docstring in the similarity checker.

    Closes #4648

•   The similarity checker no longer add three trailing whitespaces for empty lines in its report.

  What's New in Pylint 2.9.2?

Release date: 2021-07-01

•   Fix a crash that happened when analysing code using type(self) to access a class attribute in the unused-private-member checker.

    Closes #4638

•   Fix a false positive for unused-private-member when accessing a private variable with self

    Closes #4644

•   Fix false-positive of unnecessary-dict-index-lookup and consider-using-dict-items for reassigned dict index lookups

    Closes #4630

  What's New in Pylint 2.9.1?

Release date: 2021-06-30

•   Upgrade astroid to 2.6.2

    Closes #4631 Closes #4633

  What's New in Pylint 2.9.0?

Release date: 2021-06-29

•   Python 3.10 is now supported.

•   Add type annotations to pyreverse dot files

    Closes #1548

•   Fix missing support for detecting deprecated aliases to existing functions/methods.

    Closes #4618

•   astroid has been upgraded to 2.6.1

•   Added various deprecated functions/methods for python 3.10, 3.7, 3.6 and 3.3

•   Fix false positive useless-type-doc on ignored argument using pylint.extensions.docparams when a function was typed using pep484 but not inside the docstring.

    Closes #4117 Closes #4593

•   setuptools_scm has been removed and replaced by tbump in order to not have hidden runtime dependencies to setuptools

•   Fix a crash when a test function is decorated with @pytest.fixture and astroid can't infer the name of the decorator when using open without with.

    Closes #4612

•   Added deprecated-decorator: Emitted when deprecated decorator is used.

    Closes #4429

•   Added ignore-paths behaviour. Defined regex patterns are matched against full file path.

    Closes #2541

•   Fix false negative for consider-using-with if calls like open() were used outside of assignment expressions.

•   The warning for arguments-differ now signals explicitly the difference it detected by naming the argument or arguments that changed and the type of change that occurred.

•   Suppress consider-using-with inside context managers.

    Closes #4430

•   Added --fail-on option to return non-zero exit codes regardless of --fail-under value.

•   numversion tuple contains integers again to fix multiple pylint's plugins that relied on it

    Closes #4420

•   Fix false-positive too-many-ancestors when inheriting from builtin classes, especially from the collections.abc module

    Closes #4166 Closes #4415

•   Stdlib deprecated modules check is moved to stdlib checker. New deprecated modules are added.

•   Fix raising false-positive no-member on abstract properties

•   Created new error message called arguments-renamed which identifies any changes at the parameter names of overridden functions.

    Closes #3536

•   New checker consider-using-dict-items. Emitted when iterating over dictionary keys and then indexing the same dictionary with the key within loop body.

    Closes #3389

•   Don't emit import-error if import guarded behind if sys.version_info >= (x, x)

•   Fix incompatibility with Python 3.6.0 caused by typing.Counter and typing.NoReturn usage

    Closes #4412

•   New checker use-maxsplit-arg. Emitted either when accessing only the first or last element of str.split().

    Closes #4440

•   Add ignore_signatures to duplicate code checker

    Closes #3619

•   Fix documentation errors in "Block disables" paragraph of User Guide.

•   New checker unnecessary-dict-index-lookup. Emitted when iterating over dictionary items (key-value pairs) and accessing the value by index lookup.

    Closes #4470

•   New checker``consider-using-from-import``. Emitted when a submodule/member of a package is imported and aliased with the same name.

    Closes #2309

•   Allow comma-separated list in output-format and separate output files for each specified format.

    Closes #1798

•   Make using-constant-test detect constant tests consisting of list literals like [] and [1, 2, 3].

•   Improved error message of unnecessary-comprehension checker by providing code suggestion.

    Closes #4499

•   New checker unused-private-member. Emitted when a private member (i.e., starts with __) of a class is defined but not used.

    Closes #4483

•   Fix false negative of consider-using-enumerate when iterating over an attribute.

    Closes #3657

•   New checker invalid-class-object. Emitted when a non-class is assigned to a __class__ attribute.

    Closes #585

•   Fix a crash when a plugin from the configuration could not be loaded and raise an error 'bad-plugin-value' instead

    Closes #4555

•   Added handling of floating point values when parsing configuration from pyproject.toml

    Closes #4518

•   invalid-length-returned, now also works when nothing at all is returned following an upgrade in astroid.

•   logging-format-interpolation and logging-not-lazy, now works on logger class created from renamed logging import following an upgrade in astroid.

•   Fix false-positive no-member with generic base class

    Closes PyCQA/astroid#942

•   Fix assigning-non-slot false-positive with base that inherits from typing.Generic

    Closes #4509 Closes PyCQA/astroid#999

•   New checker invalid-all-format. Emitted when __all__ has an invalid format, i.e. isn't a tuple or list.

•   Fix false positive unused-variable and undefined-variable with Pattern Matching in Python 3.10

•   New checker await-outside-async. Emitted when await is used outside an async function.

•   Clarify documentation for typing extension.

    Closes #4545

•   Add new extension CodeStyleChecker. It includes checkers that can improve code consistency. As such they don't necessarily provide a performance benefit and are often times opinionated.

•   New checker consider-using-tuple. Emitted when an in-place defined list or set can be replaced by a tuple.

•   New checker consider-using-namedtuple-or-dataclass. Emitted when dictionary values can be replaced by namedtuples or dataclass instances.

•   Fix error that occurred when using slice as subscript for dict.

•   Reduce false-positives around inference of .value and .name properties on Enum subclasses, following an upgrade in astroid

    Closes #1932 Closes #2062

•   Fix issue with cached_property that caused invalid-overridden-method error when overriding a property.

    Closes #4023

•   Fix unused-import false positive for imported modules referenced in attribute lookups in type comments.

    Closes #4603

  What's New In Pylint 2.8

From pylint's beginning to pylint 2.14.0 included, we had a changelog that contained all nontrivial changes to Pylint, including changes that were not user facing, i.e. change that might interest you only if you're a developer working on pylint or pylint plugins or an open-source historian.

From pylint 1.6.0 to 2.14.0, on top of the full changelog there was also a summary of (mostly user facing) changes.

  Summary -- Release highlights

  Breaking changes

•   The 'doc' extra-require has been removed. __pkginfo__` does not contain the package metadata anymore (except numversion, until 3.0). Meta-information are accessible with

    `python from importlib import metadata metadata.metadata('pylint') ` Prefer that to an import from __pkginfo__.

  New checkers

•   New refactoring message consider-using-with. This message is emitted if resource-allocating functions or methods of the standard library (like open() or threading.Lock.acquire()) that can be used as a context manager are called without a with block.

•   Add deprecated-argument check for deprecated arguments.

•   Add new extension ConfusingConsecutiveElifChecker. This optional checker emits a refactoring message (R5601 confusing-consecutive-elif) if if/elif statements with different indentation levels follow directly one after the other.

•   Add consider-using-min-max-builtin check for if statement which could be replaced by Python builtin min or max.

•   Add new extension TypingChecker. This optional checker can detect the use of deprecated typing aliases and can suggest the use of the alternative union syntax where possible. (For example, 'typing.Dict' can be replaced by 'dict', and 'typing.Unions' by '|', etc.) Make sure to check the config options if you plan on using it!

•   Add deprecated-class check for deprecated classes.

  Other Changes

•   New option --output=<file> to output result to a file rather than printing to stdout.

    Closes #1070

•   Reduce usage of blacklist/whitelist terminology. Notably, extension-pkg-allow-list is an alternative to extension-pkg-whitelist and the message blacklisted-name is now emitted as disallowed-name. The previous names are accepted to maintain backward compatibility.

•   The packaging is now done via setuptools exclusively. doc, tests, man, elisp and Changelog are not packaged anymore - reducing the size of the package by 75%.

•   Updated astroid to 2.5.4

•   COPYING has been renamed to LICENSE for standardization.

  Full changelog

  What's New in Pylint 2.8.3?

Release date: 2021-05-31

•   Astroid has been pinned to 2.5.6 for the 2.8 branch.

    Refs #4527

  What's New in Pylint 2.8.2?

Release date: 2021-04-26

•   Keep __pkginfo__.numversion a tuple to avoid breaking pylint-django.

    Closes #4405

•   scm_setuptools has been added to the packaging.

•   Pylint's tags are now the standard form vX.Y.Z and not pylint-X.Y.Z anymore.

•   New warning message deprecated-class. This message is emitted if import or call deprecated class of the standard library (like collections.Iterable that will be removed in Python 3.10).

    Closes #4388

  What's New in Pylint 2.8.1?

Release date: 2021-04-25

•   Add numversion back (temporarily) in __pkginfo__ because it broke Pylama and revert the unnecessary pylint.version breaking change.

    Closes #4399

  What's New in Pylint 2.8.0?

Release date: 2021-04-24

•   New refactoring message consider-using-with. This message is emitted if resource-allocating functions or methods of the standard library (like open() or threading.Lock.acquire()) that can be used as a context manager are called without a with block.

    Closes #3413

•   Resolve false positives on unused variables in decorator functions

    Closes #4252

•   Add new extension ConfusingConsecutiveElifChecker. This optional checker emits a refactoring message (R5601 confusing-consecutive-elif) if if/elif statements with different indentation levels follow directly one after the other.

•   New option --output=<file> to output result to a file rather than printing to stdout.

    Closes #1070

•   Use a prescriptive message for unidiomatic-typecheck

    Closes #3891

•   Apply const-naming-style to module constants annotated with typing.Final

•   The packaging is now done via setuptools exclusively. doc, tests, man, elisp and Changelog are not packaged anymore - reducing the size of the package by 75%.

•   Debian packaging is now (officially) done in https://salsa.debian.org/python-team/packages/pylint.

•   The 'doc' extra-require has been removed.

•   __pkginfo__ now only contain __version__ (also accessible with pylint.__version__), other meta-information are still accessible with from importlib import metadata;metadata.metadata('pylint').

•   COPYING has been renamed to LICENSE for standardization.

•   Fix false-positive used-before-assignment in function returns.

    Closes #4301

•   Updated astroid to 2.5.3

    Closes #2822, #4206, #4284

•   Add consider-using-min-max-builtin check for if statement which could be replaced by Python builtin min or max

    Closes #3406

•   Don't auto-enable postponed evaluation of type annotations with Python 3.10

•   Update astroid to 2.5.4

•   Add new extension TypingChecker. This optional checker can detect the use of deprecated typing aliases and can suggest the use of the alternative union syntax where possible. (For example, 'typing.Dict' can be replaced by 'dict', and 'typing.Unions' by '|', etc.) Make sure to check the config options if you plan on using it!

•   Reactivates old counts in report mode.

    Closes #3819

•   During detection of inconsistent-return-statements consider that assert False is a return node.

    Closes #4019

•   Run will not fail if score exactly equals config.fail_under.

•   Functions that never returns may declare NoReturn as type hints, so that inconsistent-return-statements is not emitted.

    Closes #4122, #4188

•   Improved protected access checks to allow access inside class methods

    Closes #1159

•   Fix issue with PEP 585 syntax and the use of collections.abc.Set

•   Fix issue that caused class variables annotated with typing.ClassVar to be identified as class constants. Now, class variables annotated with typing.Final are identified as such.

    Closes #4277

•   Continuous integration with read the doc has been added.

    Closes #3850

•   Don't show DuplicateBasesError for attribute access

•   Fix crash when checking setup.cfg for pylint config when there are non-ascii characters in there

    Closes #4328

•   Allow code flanked in backticks to be skipped by spellchecker

    Closes #4319

•   Allow Python tool directives (for black, flake8, zimports, isort, mypy, bandit, pycharm) at beginning of comments to be skipped by spellchecker

    Closes #4320

•   Fix issue that caused Emacs pylint to fail when used with tramp

•   Improve check for invalid PEP 585 syntax inside functions if postponed evaluation of type annotations is enabled

•   Improve check for invalid PEP 585 syntax as default function arguments

  What's New In Pylint 2.7

From pylint's beginning to pylint 2.14.0 included, we had a changelog that contained all nontrivial changes to Pylint, including changes that were not user facing, i.e. change that might interest you only if you're a developer working on pylint or pylint plugins or an open-source historian.

From pylint 1.6.0 to 2.14.0, on top of the full changelog there was also a summary of (mostly user facing) changes.

  Summary -- Release highlights

•   Python 3.6+ is now required.

•   No more duplicate messages when using multiple jobs.

•   Handling of the new typing provided by mypy 0.8

•   Reduced the number of false positives in general

•   Reduced the occurrence of genuinely large recursion that went above system limit (See #3836, for a fix for pandas)

  New checkers

•   Add nan-comparison check for comparison of NaN values

•   Add support to ignored-argument-names in DocstringParameterChecker and adds useless-param-doc and useless-type-doc messages.

•   Add empty-comment check for empty comments.

•   Add simplifiable-condition check for extraneous constants in conditionals using and/or.

•   Add condition-evals-to-constant check for conditionals using and/or that evaluate to a constant.

•   Add consider-using-generator check for the use of list comprehension inside any or all function.

  Other Changes

•   Fix false positive for builtin-not-iterating when zip or map receives iterable

•   Fix linter multiprocessing pool shutdown which triggered warnings when ran in parallels with other pytest plugins.

•   Enums are now required to be named in UPPER_CASE by invalid-name.

•   Fix bug that lead to duplicate messages when using --jobs 2 or more.

•   Adds option check-protected-access-in-special-methods in the ClassChecker to activate/deactivate protected-access message emission for single underscore prefixed attribute in special methods.

•   inconsistent-return-statements message is now emitted if one of try/except statement is not returning explicitly while the other do.

•   Fix false positive message useless-super-delegation when default keyword argument is a dictionary.

•   Fix vulnerable regular expressions in pyreverse. The ambiguities of vulnerable regular expressions are removed, making the repaired regular expressions safer and faster matching.

•   len-as-conditions is now triggered only for classes that are inheriting directly from list, dict, or set and not implementing the __bool__ function, or from generators like range or list/dict/set comprehension. This should reduce the false positive for other classes, like pandas's DataFrame or numpy's Array.

•   Fixes duplicate code detection for --jobs=2+

•   New option allowed-redefined-builtins defines variable names allowed to shadow builtins.

•   Improved protected access checks to allow access inside class methods

  Full changelog

  What's New in Pylint 2.7.4?

Release date: 2021-03-30

•   Fix a problem with disabled msgid not being ignored

    Closes #4265

•   Fix issue with annotated class constants

    Closes #4264

  What's New in Pylint 2.7.3?

Release date: 2021-03-29

•   Introduce logic for checking deprecated attributes in DeprecationMixin.

•   Reduce usage of blacklist/whitelist terminology. Notably, extension-pkg-allow-list is an alternative to extension-pkg-whitelist and the message blacklisted-name is now emitted as disallowed-name. The previous names are accepted to maintain backward compatibility.

•   Move deprecated checker to DeprecatedMixin

    Closes #4086

•   Bump astroid version to 2.5.2

•   Fix false positive for method-hidden when using private attribute and method

    Closes #3936

•   use-symbolic-message-instead now also works on legacy messages like C0111 (missing-docstring).

•   Remove unwanted print to stdout from _emit_no_member

•   Introduce a command-line option to specify pyreverse output directory

    Closes #4159

•   Fix issue with Enums and class-attribute-naming-style=snake_case

    Closes #4149

•   Add allowed-redefined-builtins option for fine tuning redefined-builtin check.

    Closes #3263

•   Fix issue when executing with python -m pylint

    Closes #4161

•   Exempt typing.TypedDict from too-few-public-methods check.

    Closes #4180

•   Fix false-positive no-member for typed annotations without default value.

    Closes #3167

•   Add --class-const-naming-style for Enum constants and class variables annotated with typing.ClassVar

    Closes #4181

•   Fix astroid.Inference error for undefined-variables with len()`

    Closes #4215

•   Fix column index on FIXME warning messages

    Closes #4218

•   Improve handling of assignment expressions, better edge case handling

    Closes #3763, #4238

•   Improve check if class is subscriptable PEP585

•   Fix documentation and filename handling of --import-graph

•   Fix false-positive for unused-import on class keyword arguments

    Closes #3202

•   Fix regression with plugins on PYTHONPATH if latter is cwd

    Closes #4252

  What's New in Pylint 2.7.2?

Release date: 2021-02-28

•   Fix False Positive on Enum.__members__.items(), Enum.__members__.values, and Enum.__members__.keys

    Closes #4123

•   Properly strip dangerous sys.path entries (not just the first one)

    Closes #3636

•   Workflow and packaging improvements

  What's New in Pylint 2.7.1?

Release date: 2021-02-23

•   Expose UnittestLinter in pylint.testutils

•   Don't check directories starting with '.' when using register_plugins

    Closes #4119

  What's New in Pylint 2.7.0?

Release date: 2021-02-21

•   Introduce DeprecationMixin for reusable deprecation checks.

    Closes #4049

•   Fix false positive for builtin-not-iterating when map receives iterable

    Closes #4078

•   Python 3.6+ is now required.

•   Fix false positive for builtin-not-iterating when zip receives iterable

•   Add nan-comparison check for NaN comparisons

•   Bug fix for empty-comment message line number.

    Closes #4009

•   Only emit bad-reversed-sequence on dictionaries if below py3.8

    Closes #3940

•   Handle class decorators applied to function.

    Closes #3882

•   Add check for empty comments

•   Fix minor documentation issue in contribute.rst

•   Enums are now required to be named in UPPER_CASE by invalid-name.

    Closes #3834

•   Add missing checks for deprecated functions.

•   Postponed evaluation of annotations are now recognized by default if python version is above 3.10

    Closes #3992

•   Fix column metadata for anomalous backslash lints

•   Drop support for Python 3.5

•   Add support for pep585 with postponed evaluation

    Closes #3320

•   Check alternative union syntax - PEP 604

    Closes #4065

•   Fix multiple false positives with assignment expressions

    Closes #3347, #3953, #3865, #3275

•   Fix TypedDict inherit-non-class false-positive Python 3.9+

    Closes #1927

•   Fix issue with nested PEP 585 syntax

•   Fix issue with nested PEP 604 syntax

•   Fix a crash in undefined-variable caused by chained attributes in metaclass

    Closes #3742

•   Fix false positive for not-async-context-manager when contextlib.asynccontextmanager is used

    Closes #3862

•   Fix linter multiprocessing pool shutdown (triggered warnings when ran in parallels with other pytest plugins)

    Closes #3779

•   Fix a false-positive emission of no-self-use and unused-argument for methods of generic structural types (Protocol[T])

    Closes #3885

•   Fix bug that lead to duplicate messages when using --jobs 2 or more.

    Closes #3584

•   Adds option check-protected-access-in-special-methods in the ClassChecker to activate/deactivate protected-access message emission for single underscore prefixed attribute in special methods.

    Closes #3120

•   Fix vulnerable regular expressions in pyreverse

    Closes #3811

•   inconsistent-return-statements message is now emitted if one of try/except statement is not returning explicitly while the other do.

    Closes #3468

•   Fix useless-super-delegation false positive when default keyword argument is a dictionary.

    Closes #3773

•   Fix a crash when a specified config file does not exist

•   Add support to ignored-argument-names in DocstringParameterChecker and adds useless-param-doc and useless-type-doc messages.

    Closes #3800

•   Enforce docparams consistently when docstring is not present

    Closes #2738

•   Fix duplicate-code false positive when lines only contain whitespace and non-alphanumeric characters (e.g. parentheses, bracket, comma, etc.)

•   Improve lint message for singleton-comparison with bools

•   Fix spell-checker crash on indented docstring lines that look like # comments

    Closes #3786

•   Fix AttributeError in checkers/refactoring.py

•   Improve sphinx directives spelling filter

•   Fix a bug with postponed evaluation when using aliases for annotations.

    Closes #3798

•   Fix minor documentation issues

•   Improve the performance of the line length check.

•   Removed incorrect deprecation of inspect.getfullargspec

•   Fix signature-differs false positive for functions with variadics

    Closes #3737

•   Fix a crash in consider-using-enumerate when encountering range() without arguments

    Closes #3735

•   len-as-conditions is now triggered only for classes that are inheriting directly from list, dict, or set and not implementing the __bool__ function, or from generators like range or list/dict/set comprehension. This should reduce the false positives for other classes, like pandas's DataFrame or numpy's Array.

    Closes #1879

•   Fixes duplicate-errors not working with -j2+

    Closes #3314

•   generated-members now matches the qualified name of members

    Closes #2498

•   Add check for bool function to len-as-condition

•   Add simplifiable-condition check for extraneous constants in conditionals using and/or.

•   Add condition-evals-to-constant check for conditionals using and/or that evaluate to a constant.

    Closes #3407

•   Changed setup.py to work with distlib

    Closes #3555

•   New check: consider-using-generator

    This check warns when a comprehension is used inside an any or all function, since it is unnecessary and should be replaced by a generator instead. Using a generator would be less code and way faster.

    Closes #3165

•   Add Github Actions to replace Travis and AppVeyor in the future

  What's New In Pylint 2.6

From pylint's beginning to pylint 2.14.0 included, we had a changelog that contained all nontrivial changes to Pylint, including changes that were not user facing, i.e. change that might interest you only if you're a developer working on pylint or pylint plugins or an open-source historian.

From pylint 1.6.0 to 2.14.0, on top of the full changelog there was also a summary of (mostly user facing) changes.

  Summary -- Release highlights

•   bad-continuation and bad-whitespace have been removed. black or another formatter can help you with this better than Pylint

•   Added support for isort 5

  New checkers

•   Add super-with-arguments check for flagging instances of Python 2 style super calls.

•   Add raise-missing-from check for exceptions that should have a cause.

  Other Changes

•   bad-continuation and bad-whitespace have been removed. black or another formatter can help you with this better than Pylint

•   The no-space-check option has been removed, it's no longer possible to consider empty line like a trailing-whitespace by using clever options.

•   mixed-indentation has been removed, it is no longer useful since TabError is included directly in python3

•   Fix superfluous-parens false-positive for the walrus operator

•   Add support for both isort 4 and isort 5. If you have pinned isort 4 in your projet requirements, nothing changes. If you use isort 5, though, note that the known-standard-library option is not interpreted the same in isort 4 and isort 5 (see the migration guide in isort documentation (no longer available) for further details). For compatibility's sake for most pylint users, the known-standard-library option in pylint now maps to extra-standard-library in isort 5. If you really want what known-standard-library now means in isort 5, you must disable the wrong-import-order check in pylint and run isort manually with a proper isort configuration file.

  Full changelog

  What's New in Pylint 2.6.1?

Release date: 2021-02-16

•   Astroid version has been set as < 2.5

    Closes #4093

  What's New in Pylint 2.6.0?

Release date: 2020-08-20

•   Fix various scope-related bugs in undefined-variable checker

    Closes #1082, #3434, #3461

•   bad-continuation and bad-whitespace have been removed, black or another formatter can help you with this better than Pylint

    Closes #246, #289, #638, #747, #1148, #1179, #1943, #2041, #2301, #2304, #2944, #3565

•   The no-space-check option has been removed. It's no longer possible to consider empty line like a trailing-whitespace by using clever options

    Closes #1368

•   missing-kwoa is no longer emitted when dealing with overload functions

    Closes #3655

•   mixed-indentation has been removed, it is no longer useful since TabError is included directly in python3

    Closes #2984 #3573

•   Add super-with-arguments check for flagging instances of Python 2 style super calls.

•   Add an faq detailing which messages to disable to avoid duplicates w/ other popular linters

•   Fix superfluous-parens false-positive for the walrus operator

    Closes #3383

•   Fix fail-under not accepting floats

•   Fix a bug with ignore-docstrings ignoring all lines in a module

•   Fix pre-commit config that could lead to undetected duplicate lines of code

•   Fix a crash in parallel mode when the module's filepath is not set

    Closes #3564

•   Add raise-missing-from check for exceptions that should have a cause.

•   Support both isort 4 and isort 5. If you have pinned isort 4 in your projet requirements, nothing changes. If you use isort 5, though, note that the known-standard-library option is not interpreted the same in isort 4 and isort 5 (see the migration guide in isort documentation for further details). For compatibility's sake for most pylint users, the known-standard-library option in pylint now maps to extra-standard-library in isort 5. If you really want what known-standard-library now means in isort 5, you must disable the wrong-import-order check in pylint and run isort manually with a proper isort configuration file.

    Closes #3722

•   Fix a crash caused by not guarding against InferenceError when calling infer_call_result

    Closes #3690

•   Fix a crash in parallel mode when the module's filepath is not set

    Closes #3564

  What's New In Pylint 2.5

From pylint's beginning to pylint 2.14.0 included, we had a changelog that contained all nontrivial changes to Pylint, including changes that were not user facing, i.e. change that might interest you only if you're a developer working on pylint or pylint plugins or an open-source historian.

From pylint 1.6.0 to 2.14.0, on top of the full changelog there was also a summary of (mostly user facing) changes.

  Summary -- Release highlights

  New checkers

•   A new check isinstance-second-argument-not-valid-type was added. This check is emitted whenever pylint finds a call to the isinstance function with a second argument that is not a type. Such code is likely unintended as it will cause a TypeError to be thrown at runtime error.

•   A new check assert-on-string-literal was added. This check is emitted whenever pylint finds an assert statement with a string literal as its first argument. Such assert statements are probably unintended as they will always pass.

•   A new check f-string-without-interpolation was added. This check is emitted whenever pylint detects the use of an f-string without having any interpolated values in it, which means that the f-string can be a normal string.

•   Multiple checks for invalid return types of protocol functions were added:

•   invalid-bool-returned: __bool__ did not return a bool

•   invalid-index-returned: __index__ did not return an integer

•   invalid-repr-returned): __repr__ did not return a string

•   invalid-str-returned): __str__ did not return a string

•   invalid-bytes-returned): __bytes__ did not return a string

•   invalid-hash-returned): __hash__ did not return an integer

•   invalid-length-hint-returned): __length_hint__ did not return a non-negative integer

•   invalid-format-returned): __format__ did not return a string

•   invalid-getnewargs-returned): __getnewargs__ did not return a tuple

•   invalid-getnewargs-ex-returned): __getnewargs_ex__ did not return a tuple of the form (tuple, dict)

•   A new check inconsistent-quotes was added. This check is emitted when quotes delimiters (" and ') are not used consistently throughout a module. It allows avoiding unnecessary escaping, allowing, for example, "Don't error" in a module in which single-quotes otherwise delimit strings so that the single quote in Don't doesn't need to be escaped.

•   A new check non-str-assignment-to-dunder-name was added to ensure that only strings are assigned to __name__ attributes.

  Other Changes

•   Configuration can be read from a setup.cfg or pyproject.toml file in the current directory. A setup.cfg must prepend pylintrc section names with pylint., for example [pylint.MESSAGES CONTROL]. A pyproject.toml file must prepend section names with tool.pylint., for example [tool.pylint.'MESSAGES CONTROL']. These files can also be passed in on the command line.

•   Add new good-names-rgx and bad-names-rgx to enable permitting or disallowing of names via regular expressions

    To enable better handling of permitted/disallowed names, we added two new config options: good-names-rgxs: a comma- separated list of regexes, that if a name matches will be exempt of naming-checking. bad-names-rgxs: a comma- separated list of regexes, that if a name matches will be always marked as a disallowed name.

•   Mutable collections.* are now flagged as dangerous defaults.

•   Add new --fail-under flag for setting the threshold for the score to fail overall tests. If the score is over the fail-under threshold, pylint will complete SystemExit with value 0 to indicate no errors.

•   Added a new option notes-rgx to make fixme warnings more flexible. Now either notes or notes-rgx option can be used to detect fixme warnings.

•   Non-ASCII characters are now allowed by invalid-name.

•   pylint no longer emits invalid-name for non-constants found at module level.

    Pylint was considering all module level variables as constants, which is not what PEP 8 is actually mandating.

•   A new check non-ascii-name was added to detect identifiers with non-ASCII characters.

•   Overloaded typing functions no longer trigger no-self-use, unused-argument, missing-docstring and similar checks that assumed that overloaded functions are normal functions.

•   python -m pylint can no longer be made to import files from the local directory.

•   A new command --list-extensions was added.

    This command lists all extensions present in pylint.extensions.

•   Various false positives have been fixed which you can read more about in the Changelog files.

•   Multiple types of string formatting are allowed in logging functions.

    The logging-fstring-interpolation message has been brought back to allow multiple types of string formatting to be used. The type of formatting to use is chosen through enabling and disabling messages rather than through the logging-format-style option. The fstr value of the logging-format-style option is not valid.

  Full changelog

  What's New in Pylint 2.5.3?

Release date: 2020-06-8

•   Fix a regression where disable comments that have checker names with numbers in them are not parsed correctly

    Closes #3666

•   property-with-parameters properly handles abstract properties

    Closes #3600

•   continue-in-finally no longer emitted on Python 3.8 where it's now valid

    Closes #3612

•   Fix a regression where messages with dash are not fully parsed

    Closes #3604

•   In a TOML configuration file, it's now possible to use rich (non-string) types, such as list, integer or boolean instead of strings. For example, one can now define a list of message identifiers to enable like this:

    enable = [
        "use-symbolic-message-instead",
        "useless-suppression",
    ]

    Closes #3538

•   Fix a regression where the score was not reported with multiple jobs

    Closes #3547

•   Protect against AttributeError when checking cell-var-from-loop

    Closes #3646

  What's New in Pylint 2.5.2?

Release date: 2020-05-05

•   pylint.Run accepts do_exit as a deprecated parameter

    Closes #3590

  What's New in Pylint 2.5.1?

Release date: 2020-05-05

•   Fix a crash in method-hidden lookup for unknown base classes

    Closes #3527

•   Revert pylint.Run's exit parameter to do_exit

    This has been inadvertently changed several releases ago to do_exit.

    Closes #3533

•   no-value-for-parameter variadic detection has improved for assign statements

    Closes #3563

•   Allow package files to be properly discovered with multiple jobs

    Closes #3524

•   Allow linting directories without __init__.py which was a regression in 2.5.

    Closes #3528

  What's New in Pylint 2.5.0?

Release date: 2020-04-27

•   Fix a false negative for undefined-variable when using class attribute in comprehension.

    Closes #3494

•   Fix a false positive for undefined-variable when using class attribute in decorator or as type hint.

    Closes #511 Closes #1976

•   Remove HTML quoting of messages in JSON output.

    Closes #2769

•   Adjust the invalid-name rule to work with non-ASCII identifiers and add the non-ascii-name rule.

    Closes #2725

•   Positional-only arguments are taken in account for useless-super-delegation

•   unidiomatic-typecheck is no longer emitted for in and not in operators

    Closes #3337

•   Positional-only argument annotations are taken in account for unused-import

    Closes #3462

•   Add a command to list available extensions.

•   Allow used variables to be properly consumed when different checks are enabled / disabled

    Closes #3445

•   Fix dangerous-default-value rule to account for keyword argument defaults

    Closes #3373

•   Fix a false positive of self-assigning-variable on tuple unpacking.

    Closes #3433

•   no-self-use is no longer emitted for typing stubs.

    Closes #3439

•   Fix a false positive for undefined-variable when __class__ is used

    Closes #3090

•   Emit invalid-name for variables defined in loops at module level.

    Closes #2695

•   Add a check for cases where the second argument to isinstance is not a type.

    Closes #3308

•   Add 'notes-rgx' option, to be used for fixme check.

    Closes #2874

•   function-redefined exempts function redefined on a condition.

    Closes #2410

•   typing.overload functions are exempted from docstring checks

    Closes #3350

•   Emit invalid-overridden-method for improper async def overrides.

    Closes #3355

•   Do not allow python -m pylint ... to import user code

    python -m pylint ... adds the current working directory as the first element of sys.path. This opens up a potential security hole where pylint will import user level code as long as that code resides in modules having the same name as stdlib or pylint's own modules.

    Closes #3386

•   Add dummy-variables-rgx option for _redeclared-assigned-name check.

    Closes #3341

•   Fixed graph creation for relative paths

•   Add a check for asserts on string literals.

    Closes #3284

•   not in is considered iterating context for some of the Python 3 porting checkers.

•   A new check inconsistent-quotes was added.

•   Add a check for non string assignment to __name__ attribute.

    Closes #583

•   __pow__, __imatmul__, __trunc__, __floor__, and __ceil__ are recognized as special method names.

    Closes #3281

•   Added errors for protocol functions when invalid return types are detected. E0304 (invalid-bool-returned): __bool__ did not return a bool E0305 (invalid-index-returned): __index__ did not return an integer E0306 (invalid-repr-returned): __repr__ did not return a string E0307 (invalid-str-returned): __str__ did not return a string E0308 (invalid-bytes-returned): __bytes__ did not return a string E0309 (invalid-hash-returned): __hash__ did not return an integer E0310 (invalid-length-hint-returned): __length_hint__ did not return a non-negative integer E0311 (invalid-format-returned): __format__ did not return a string E0312 (invalid-getnewargs-returned): __getnewargs__ did not return a tuple E0313 (invalid-getnewargs-ex-returned): __getnewargs_ex__ did not return a tuple of the form (tuple, dict)

    Closes #560

•   missing-*-docstring can look for __doc__ assignments.

    Closes #3301

•   undefined-variable can now find undefined loop iterables

    Closes #498

•   safe_infer can infer a value as long as all the paths share the same type.

    Closes #2503

•   Add a --fail-under <score> flag, also configurable in a .pylintrc file. If the final score is more than the specified score, it's considered a success and pylint exits with exitcode 0. Otherwise, it's considered a failure and pylint exits with its current exitcode based on the messages issued.

    Closes #2242

•   Don't emit line-too-long for multilines when disable=line-too-long comment stands at their end

    Closes #2957

•   Fixed an AttributeError caused by improper handling of dataclasses inference in pyreverse

    Closes #3256

•   Do not exempt bare except from undefined-variable and similar checks

    If a node was wrapped in a TryExcept, pylint was taking a hint from the except handler when deciding to emit or not a message. We were treating bare except as a fully fledged ignore but only the corresponding exceptions should be handled that way (e.g. NameError or ImportError)

    Closes #3235

•   No longer emit assignment-from-no-return when a function only raises an exception

    Closes #3218

•   Allow import aliases to exempt import-error when used in type annotations.

    Closes #3178

•   Ellipsis` is exempted from ``multiple-statements for function overloads.

    Closes #3224

•   No longer emit invalid-name for non-constants found at module level.

    Pylint was taking the following statement from PEP-8 too far, considering all module level variables as constants, which is not what the statement is saying:

    Constants are usually defined on a module level and written in all capital letters with underscores separating words.

    Closes #3111 Closes #3132

•   Allow implicit-str-concat-in-sequence to be emitted for string juxtaposition

    Closes #3030

•   implicit-str-concat-in-sequence was renamed implicit-str-concat

•   The json reporter no longer bypasses redirect_stdout.

    Closes #3227

•   Move NoFileError, OutputLine, FunctionalTestReporter, FunctionalTestFile, LintModuleTest and related methods from test_functional.py to pylint.testutils to help testing for 3rd party pylint plugins.

•   Can read config from a setup.cfg or pyproject.toml file.

    Closes #617

•   Fix exception-escape false positive with generators

    Closes #3128

•   inspect.getargvalues is no longer marked as deprecated.

•   A new check f-string-without-interpolation was added

    Closes #3190

•   Flag mutable collections.* utilities as dangerous defaults

    Closes #3183

•   docparams extension supports multiple types in raises sections.

    Multiple types can also be separated by commas in all valid sections.

    Closes #2729

•   Allow parallel linting when run under Prospector

•   Fixed false positives of method-hidden when a subclass defines the method that is being hidden.

    Closes #414

•   Python 3 porting mode is 30-50% faster on most codebases

•   Python 3 porting mode no longer swallows syntax errors

    Closes #2956

•   Pass the actual PyLinter object to sub processes to allow using custom PyLinter classes.

    PyLinter object (and all its members except reporter) needs to support pickling so the PyLinter object can be passed to worker processes.

•   Clean up setup.py

    Make pytest-runner a requirement only if running tests, similar to McCabe.

    Clean up the setup.py file, resolving a number of warnings around it.

•   Handle SyntaxError in files passed via --from-stdin option

    Pylint no longer outputs a traceback, if a file, read from stdin, contains a syntaxerror.

•   Fix uppercase style to disallow 3+ uppercase followed by lowercase.

•   Fixed undefined-variable and unused-import false positives when using a metaclass via an attribute.

    Closes #1603

•   Emit unused-argument for functions that partially uses their argument list before raising an exception.

    Closes #3246

•   Fixed broad_try_clause extension to check try/finally statements and to check for nested statements (e.g., inside of an if statement).

•   Recognize classes explicitly inheriting from abc.ABC or having an abc.ABCMeta metaclass as abstract. This makes them not trigger W0223.

    Closes #3098

•   Fix overzealous arguments-differ when overridden function uses variadics

    No message is emitted if the overriding function provides positional or keyword variadics in its signature that can feasibly accept and pass on all parameters given by the overridden function.

    Closes #1482 Closes #1553

•   Multiple types of string formatting are allowed in logging functions.

    The logging-fstring-interpolation message has been brought back to allow multiple types of string formatting to be used.

    Closes #3361

  What's New In Pylint 2.4

From pylint's beginning to pylint 2.14.0 included, we had a changelog that contained all nontrivial changes to Pylint, including changes that were not user facing, i.e. change that might interest you only if you're a developer working on pylint or pylint plugins or an open-source historian.

From pylint 1.6.0 to 2.14.0, on top of the full changelog there was also a summary of (mostly user facing) changes.

  Summary -- Release highlights

  New checkers

•   import-outside-toplevel

    This check warns when modules are imported from places other than a module toplevel, e.g. inside a function or a class.

•   Added a new check, consider-using-sys-exit

    This check is emitted when we detect that a quit() or exit() is invoked instead of sys.exit(), which is the preferred way of exiting in program.

    Closes #2925

•   Added a new check, arguments-out-of-order

    This check warns if you have arguments with names that match those in a function's signature but you are passing them in to the function in a different order.

    Closes #2975

•   Added new checks, no-else-break and no-else-continue

    These checks highlight unnecessary else and elif blocks after break and continue statements.

    Closes #2327

•   Added unnecessary-comprehension that detects unnecessary comprehensions.

    This check is emitted when pylint finds list-, set- or dict-comprehensions, that are unnecessary and can be rewritten with the list-, set- or dict-constructors.

    Closes #2905

•   Added a new check, invalid-overridden-method

    This check is emitted when we detect that a method is overridden as a property or a property is overridden as a method. This can indicate a bug in the application code that will trigger a runtime error.

    Closes #2670

•   Added a new check, redeclared-assigned-name

    This check is emitted when pylint detects that a name was assigned one or multiple times in the same assignment, which indicate a potential bug.

    Closes #2898

•   Added a new check, self-assigning-variable

    This check is emitted when we detect that a variable is assigned to itself, which might indicate a potential bug in the code application.

    For example, the following would raise this warning:

    def new_a(attr, attr2):
      a_inst = Aclass()
      a_inst.attr2 = attr2
      # should be: a_inst.attr = attr, but have a typo
      attr = attr
      return a_inst

    Closes #2930

•   Added a new check property-with-parameters which detects when a property has more than a single argument.

    Closes #3006

•   Added subprocess-run-check to handle subprocess.run without explicitly set check keyword.

    Closes #2848

•   We added a new check message dict-iter-missing-items. This is emitted when trying to iterate through a dict in a for loop without calling its .items() method.

    Closes #2761

•   We added a new check message missing-parentheses-for-call-in-test. This is emitted in case a call to a function is made inside a test but it misses parentheses.

•   A new check class-variable-slots-conflict was added.

    This check is emitted when pylint finds a class variable that conflicts with a slot name, which would raise a ValueError at runtime.

    For example, the following would raise an error:

    class A:
        __slots__ = ('first', 'second')
        first = 1

•   A new check preferred-module was added.

    This check is emitted when pylint finds an imported module that has a preferred replacement listed in preferred-modules.

    For example, you can set the preferred modules as xml:defusedxml,json:ujson to make pylint suggest using defusedxml instead of xml and ujson rather than json.

•   A new extension broad_try_clause was added.

    This extension enforces a configurable maximum number of statements inside of a try clause. This facilitates enforcing PEP 8's guidelines about try / except statements and the amount of code in the try clause.

    You can enable this extension using --load-plugins=pylint.extensions.broad_try_clause and you can configure the amount of statements in a try statement using --max-try-statements.

  Other Changes

•   Don't emit protected-access when a single underscore prefixed attribute is used inside a special method

    Closes #1802

•   len-as-condition now only fires when a len(x) call is made without an explicit comparison.

    The message and description accompanying this checker has been changed reflect this new behavior, by explicitly asking to either rely on the fact that empty sequence are false or to compare the length with a scalar.

    OK:

    if len(x) == 0:
      pass
    while not len(x) == 0:
      pass
    assert len(x) > 5, message

    KO:

    if not len(x):
      pass
    while len(x) and other_cond:
      pass
    assert len(x), message

•   A file is now read from stdin if the --from-stdin flag is used on the command line. In addition to the --from-stdin flag a (single) file name needs to be specified on the command line, which is needed for the report.

•   The checker for ungrouped imports is now more permissive.

    The import can now be sorted alphabetically by import style. This makes pylint compatible with isort.

    The following imports do not trigger an ungrouped-imports anymore

    import unittest
    import zipfile
    from unittest import TestCase
    from unittest.mock import MagicMock

•   The checker for missing return documentation is now more flexible.

    The following does not trigger a missing-return-doc anymore

    def my_func(self):
        """This is a docstring.
        Returns
        -------
        :obj:`list` of :obj:`str`
            List of strings
        """
        return ["hi", "bye"] #@

•   signature-mutators CLI and config option was added.

    With this option, users can choose to ignore too-many-function-args, unexpected-keyword-arg, and no-value-for-parameter for functions decorated with decorators that change the signature of a decorated function.

    For example a test may want to make use of hypothesis. Adding hypothesis.extra.numpy.arrays to signature_mutators would mean that no-value-for-parameter would not be raised for:

    @given(img=arrays(dtype=np.float32, shape=(3, 3, 3, 3)))
    def test_image(img):
        ...

•   Allow the option of f-strings as a valid logging string formatting method.

    logging-fstring--interpolation has been merged into logging-format-interpolation to allow the logging-format-style option to control which logging string format style is valid. To allow this, a new fstr value is valid for the logging-format-style option.

•   --list-msgs-enabled command was added.

    When enabling/disabling several messages and groups in a config file, it can be unclear which messages are actually enabled and which are disabled. This new command produces the final resolved lists of enabled/disabled messages, sorted by symbol but with the ID provided for use with --help-msg.

  Full changelog

  What's New in Pylint 2.4.4?

Release date: 2019-11-13

•   Exempt all the names found in type annotations from unused-import

    The previous code was assuming that only typing names need to be exempted, but we need to do that for the rest of the type comment names as well.

    Closes #3112

•   Relax type import detection for names that do not come from the typing module

    Closes #3191

  What's New in Pylint 2.4.3?

Release date: 2019-10-18

•   Fix an issue with unnecessary-comprehension in comprehensions with additional repacking of elements.

    Closes #3148

•   import-outside-toplevel is emitted for ImportFrom nodes as well.

    Closes #3175

•   Do not emit no-method-argument for functions using positional only args.

    Closes #3161

•   consider-using-sys-exit is no longer emitted when exit is imported in the local scope.

    Closes #3147

•   invalid-overridden-method takes abc.abstractproperty in account

    Closes #3150

•   Fixed missing-yield-type-doc getting incorrectly raised when a generator does not document a yield type but has a type annotation.

    Closes #3185

•   typing.overload functions are exempted from too-many-function-args

    Closes #3170

  What's New in Pylint 2.4.2?

Release date: 2019-09-30

•   ignored-modules can skip submodules.

    Closes #3135

•   self-assigning-variable skips class level assignments.

    Closes #2930

•   consider-using-sys-exit is exempted when exit() is imported from sys

    Closes #3145

•   Exempt annotated assignments without variable from class-variable-slots-conflict

    Closes #3141

•   Fix utils.is_error to account for functions returning early.

    This fixes a false negative with unused-variable which was no longer triggered when a function raised an exception as the last instruction, but the body of the function still had unused variables.

    Closes #3028

  What's New in Pylint 2.4.1?

Release date: 2019-09-25

•   Exempt type checking definitions defined in both clauses of a type checking guard

    Closes #3127

•   Exempt type checking definitions inside the type check guard

    In a7f236528bb3758886b97285a56f3f9ce5b13a99 we added basic support for emitting used-before-assignment if a variable was only defined inside a type checking guard (using TYPE_CHECKING variable from typing) Unfortunately that missed the case of using those type checking imports inside the guard itself, which triggered spurious used-before-assignment errors.

    Closes #3119

•   Require astroid >= 2.3 to avoid any compatibility issues.

  What's New in Pylint 2.4.0?

Release date: 2019-09-24

•   New check: import-outside-toplevel

    This check warns when modules are imported from places other than a module toplevel, e.g. inside a function or a class.

•   Handle inference ambiguity for invalid-format-index

    Closes #2752

•   Removed Python 2 specific checks such as relative-import, invalid-encoded-data, missing-super-argument.

•   Support forward references for function-redefined check.

    Closes #2540

•   Handle redefinitions in case of type checking imports.

    Closes #2834

•   Added a new check, consider-using-sys-exit

    This check is emitted when we detect that a quit() or exit() is invoked instead of sys.exit(), which is the preferred way of exiting in program.

    Closes #2925

•   useless-suppression check now ignores cyclic-import suppressions, which could lead to false postiives due to incomplete context at the time of the check.

    Closes #3064

•   Added new checks, no-else-break and no-else-continue

    These checks highlight unnecessary else and elif blocks after break and continue statements.

    Closes #2327

•   Don't emit protected-access when a single underscore prefixed attribute is used inside a special method

    Closes #1802

•   Fix the "statement" values in the PyLinter's stats reports by module.

•   Added a new check, invalid-overridden-method

    This check is emitted when we detect that a method is overridden as a property or a property is overridden as a method. This can indicate a bug in the application code that will trigger a runtime error.

    Closes #2670

•   Added a new check, arguments-out-of-order

    This check warns if you have arguments with names that match those in a function's signature but you are passing them in to the function in a different order.

    Closes #2975

•   Added a new check, redeclared-assigned-name

    This check is emitted when pylint detects that a name was assigned one or multiple times in the same assignment, which indicate a potential bug.

    Closes #2898

•   Ignore lambda calls with variadic arguments without a context.

    Inferring variadic positional arguments and keyword arguments will result into empty Tuples and Dicts, which can lead in some cases to false positives with regard to no-value-for-parameter. In order to avoid this, until we'll have support for call context propagation, we're ignoring such cases if detected. We already did that for function calls, but the previous fix was not taking in consideration lambdas

    Closes #2918

•   Added a new check, self-assigning-variable. This check is emitted when we detect that a variable is assigned to itself, which might indicate a potential bug in the code application.

    Closes #2930

•   Added a new check, property-with-parameters.

    This check is emitted when we detect that a defined property also has parameters, which are useless.

    Closes #3006

•   Excluded protocol classes from a couple of checks.

    Closes #3002.

•   Add a check unnecessary-comprehension that detects unnecessary comprehensions.

    This check is emitted when pylint finds list-, set- or dict-comprehensions, that are unnecessary and can be rewritten with the list-, set- or dict-constructors.

    Closes #2905

•   Excluded PEP 526 instance and class variables from no-member.

    Closes #2945

•   Excluded attrs from too-few-public-methods check.

    Closes #2988.

•   unused-import emitted for the right import names in function scopes.

    Closes #2928

•   Dropped support for Python 3.4.

•   assignment-from-no-return not triggered for async methods.

    Closes #2902

•   Don't emit attribute-defined-outside-init for variables defined in setters.

    Closes #409

•   Syntax errors report the column number.

    Closes #2914

•   Support fully qualified typing imports for type annotations.

    Closes #2915

•   Exclude __dict__ from attribute-defined-outside-init

•   Fix pointer on spelling check when the error are more than one time in the same line.

    Closes #2895

•   Fix crash happening when parent of called object cannot be determined

•   Allow of in GoogleDocstring.re_multiple_type

•   Added subprocess-run-check to handle subrocess.run without explicitly set check keyword.

    Closes #2848

•   When we can't infer bare except handlers, skip try-except-raise

    Closes #2853

•   Handle more unnecessary-lambda cases when dealing with additional kwargs in wrapped calls

    Closes #2845

•   Better postponed evaluation of annotations handling

    Closes #2847

•   Support postponed evaluation of annotations for variable annotations.

    Closes #2838

•   epylint.py_run defaults to python in case the current executable is not a Python one.

    Closes #2837

•   Ignore raw docstrings when running Similarities checker with ignore-docstrings=yes option

•   Fix crash when calling inherit_from_std_ex on a class which is its own ancestor

    Closes #2680

•   Added a new check that warns the user if a function call is used inside a test but parentheses are missing.

    Closes #2658

•   len-as-condition now only fires when a len(x) call is made without an explicit comparison

    The message and description accompanying this checker has been changed reflect this new behavior, by explicitly asking to either rely on the fact that empty sequence are false or to compare the length with a scalar.

    Closes #2684

•   Add preferred-module checker that notify if an import has a replacement module that should be used.

    This check is emitted when pylint finds an imported module that has a preferred replacement listed in preferred-modules.

•   assigning-non-slot not emitted for classes with unknown base classes.

    Closes #2807

•   old-division is not emitted for non-Const nodes.

    Closes #2808

•   Added method arguments to the dot writer for pyreverse.

    Closes #2139

•   Support for linting file from stdin.

    IDEs may benefit from the support for linting from an in-memory file.

    Closes #1187

•   Added a new check class-variable-slots-conflict

    This check is emitted when pylint finds a class variable that conflicts with a slot name, which would raise a ValueError at runtime.

•   Added new check: dict-iter-missing-items (E1141)

    Closes #2761

•   Fix issue with pylint name in output of python -m pylint --version

    Closes #2764

•   Relicense logo material under the CC BY-SA 4.0 license.

•   Skip if expressions from f-strings for the check_elif checker

    Closes #2816

•   C0412 (ungrouped-import) is now compatible with isort.

    Closes #2806

•   Added new extension to detect too much code in a try clause

    Closes #2877

•   signature-mutators option was added. With this option, users can choose to ignore too-many-function-args, unexpected-keyword-arg, and no-value-for-parameter for functions decorated with decorators that change the signature of a decorated function.

    Closes #259

•   Fixed a pragma comment on its own physical line being ignored when part of a logical line with the previous physical line.

    Closes #199

•   Fixed false undefined-loop-variable for a function defined in the loop, that uses the variable defined in that loop.

    Closes #202

•   Fixed unused-argument and function-redefined getting raised for functions decorated with typing.overload.

    Closes #1581

•   Fixed a false positive with consider-using-dict-comprehension for constructions that can't be converted to a comprehension

    Closes #2963

•   Added __post_init__ to defining-attr-methods in order to avoid attribute-defined-outside-init in dataclasses.

    Closes #2581

•   Changed description of W0199 to use the term 2-item-tuple instead of 2-uple.

•   Allow a . as a prefix for Sphinx name resolution.

•   Checkers must now keep a 1 to 1 relationship between "msgid" (ie: C1234) and "symbol" (i.e. : human-readable-symbol)

•   In checkers, an old_names can now be used for multiple new messages and pylint is now a little faster

    It means if you do a partial old_names for a message definition an exception will tell you that you must rename the associated identification.

•   Allow the choice of f-strings as a valid way of formatting logging strings.

    Closes #2395

•   Added --list-msgs-enabled command to list all enabled and disabled messages given the current RC file and command line arguments.

  What's New In Pylint 2.3

From pylint's beginning to pylint 2.14.0 included, we had a changelog that contained all nontrivial changes to Pylint, including changes that were not user facing, i.e. change that might interest you only if you're a developer working on pylint or pylint plugins or an open-source historian.

From pylint 1.6.0 to 2.14.0, on top of the full changelog there was also a summary of (mostly user facing) changes.

  Summary -- Release highlights

•   This release improves the performance of the 2.X series after it was affected by a performance regression a couple of releases ago.

  New checkers

•   We added a new check message wrong-exception-operation. This is emitted when an operation is done against an exception, but the operation is not valid for the exception in question. Usually emitted when having binary operations between exceptions in except handlers.

    Closes #2494

•   We added a new no-else-raise warning similar to no-else-return

    Closes #2558

•   We added a new option check-str-concat-over-line-jumps to check implicit-str-concat-in-sequence over multiple lines.

  Other Changes

Quite a lot of bug fixes and improvements went into this release, here's a handful of them. For the full changes, check the full changelog.

•   We no longer emit *-not-iterating checks for builtins consumed by itertools

•   We fixed some false positives for no-self-argument and unsubscriptable-object when using __class_getitem__ (new in Python 3.7)

•   pylint now supports Ellipsis as a synonym for pass statements.

•   fixme gets triggered only on comments.

•   pylint exempts starred unpacking from *-not-iterating Python 3 checks.

•   compare-to-zero is now less zealous by checking against equality and identity.

    ``yield from`` is exempted from ``-not-iterating`` Python 3 checks.

•   A false positive with not-async-context-manager caused by not understanding contextlib.asynccontextmanager was fixed.

•   We refactored bad-reversed-sequence to account for more objects that can define __reversed__.

•   no-member is now emitted for enums when they lack a member.

•   Plugins can now use the load_configuration() hook. This hook is executed after configuration is loaded to prevent overwriting plugin specific configuration via user-based configuration.

•   There's a new command line option list-groups for listing all the check groups pylint knows about. This is useful to know what groups you can disable or enable individually.

  Full changelog

  What's New in Pylint 2.3.0?

Release date: 2019-02-27

•   Protect against NonDeducibleTypeHierarchy when calling semi-private is_subtype

    astroid.helpers.is_subtype raises NonDeducibleTypeHierarchy when it cannot infer the base classes of the given types, but that makes sense in its context given that the method is mostly used to inform the inference process about the hierarchy of classes. Doesn't make that much sense for pylint itself, which is why we're handling the exception here, rather than in astroid

    Closes PyCQA/astroid#644

•   Added a new command line option list-groups for listing all the check groups pylint knows about.

•   Allow BaseException for emitting broad-except, just like Exception.

    Closes #2741

•   Fixed a crash that occurred for bad-str-strip-call when strip() received None

    Closes #2743

•   Don't emit *-not-iterating checks for builtins consumed by itertools

    Closes #2731

•   Fix a crash caused by iterating over Uninferable in a string formatting check.

    Closes #2727

•   Fixed false positives for no-self-argument and unsubscriptable-object when using __class_getitem__ (new in Python 3.7)

    Closes #2416

•   Support Ellipsis as a synonym for pass statements.

    Closes #2718

•   fixme gets triggered only on comments.

    Closes #2321

•   Fixed a false positive for unused-variable and nonlocal assignments

    Closes #2671

•   Added load_configuration() hook for plugins

    New optional hook for plugins is added: load_configuration(). This hook is executed after configuration is loaded to prevent overwriting plugin specific configuration via user-based configuration.

    Closes #2635

•   Fix missing-raises-doc false positive (W9006)

    Closes #1502

•   Exempt starred unpacking from *-not-iterating Python 3 checks

    Closes #2651

•   Make compare-to-zero less zealous by checking against equality and identity

    Closes #2645

•   Add no-else-raise warning (R1720)

    Closes #2558

•   Exempt yield from from *-not-iterating Python 3 checks.

    Closes #2643

•   Fix incorrect generation of no-else-return warnings (R1705)

    Fixed issue where if statements with nested if statements were incorrectly being flagged as no-else-return in some cases and not being flagged as no-else-return in other cases. Added tests for verification and updated pylint source files to eliminate newly exposed warnings.

•   Fix false positive with not-async-context-manager caused by not understanding contextlib.asynccontextmanager

    Closes #2440

•   Refactor bad-reversed-sequence to account for more objects that can define __reversed__

    One such object would be an enum class, for which __reversed__ yields each individual enum. As such, the check for bad-reversed-sequence needs to not differentiate between classes and instances when it comes for checking of __reversed__ presence.

    Closes #2598

•   Added wrong-exception-operation

    Used when an operation is done against an exception, but the operation is not valid for the exception in question. Usually emitted when having binary operations between exceptions in except handlers.

    Closes #2494

•   no-member is emitted for enums when they lack a member

    Previously we weren't doing this because we detected a __getattr__ implementation on the Enum class (and this check is skipped for classes with __getattr__), but that is fine for Enums, given that they are inferred in a customised way in astroid.

    Closes #2565

•   Generalize chained-comparison

    Previous version incorrectly detects a < b < c and b < d and fails to detect a < b < c and c < d.

•   Avoid popping __main__ when using multiple jobs

    Closes #2689

•   Add a new option 'check-str-concat-over-line-jumps' to check 'implicit-str-concat-in-sequence'

•   Fixes for the new style logging format linter.

    The number of arguments was not handled properly, leading to an always successful check.

•   Fix false positive not-callable for uninferable properties.

•   Fix false positive useless-else-on-loop if the break is deep in the else of an inner loop.

•   Minor improvements to the help text for a few options.

  What's New In Pylint 2.2

From pylint's beginning to pylint 2.14.0 included, we had a changelog that contained all nontrivial changes to Pylint, including changes that were not user facing, i.e. change that might interest you only if you're a developer working on pylint or pylint plugins or an open-source historian.

From pylint 1.6.0 to 2.14.0, on top of the full changelog there was also a summary of (mostly user facing) changes.

  Summary -- Release highlights

  New checkers

•   String checker now reports format string type mismatches.

•   duplicate-string-formatting-argument was added for detecting duplicate string formatting arguments that should be passed instead as named arguments.

•   logging-format-style is a new option for the logging checker for usage of str.format() style format strings in calls to loggers.

    It accepts two options: --logging-format-style=old for using % style formatting, which is the assumed default, and --logging-format-style=new for using {} style formatting.

•   implicit-str-concat-in-sequence detects string concatenation inside lists, sets & tuples.

    Example of code that would generate such warning:

    woops = ('a', 'b' 'c')

  Other Changes

•   try-except-raise checker now handles multilevel inheritance hirerachy for exceptions correctly.

    Closes #2484

•   Ignore import x.y.z as z cases for checker useless-import-alias.

•   unnecessary-pass is now also emitted when a function or class contains only docstring and pass statement, in which case, docstring is enough for empty definition.

•   Fix false positive undefined-variable and used-before-assignment with nonlocal keyword usage.

•   Fix exceptions being raised when one of the params is not a ClassDef for checkers.utils.is_subclass_of.

•   pylint now picks the latest value from the inferred values of the exception that gets raised, when looking for raising-non-exception. This helps when reusing a variable name for multiple types, since pylint was picking just the first inferred value, leading to spurious false positives.

    Closes #2431

•   pylint used to emit a not-an-iterable error when looking at coroutines built with asyncio.coroutine. This is no longer the case as we handle coroutines explicitly.

    Closes #996

•   pylint used to emit an unused-variable error if unused import was found in the function. Now instead of unused-variable, unused-import is emitted.

    Closes #2421

  Full changelog

  What's New in Pylint 2.2.2?

Release date: 2018-11-28

•   Change the logging-format-style to use name identifier instead of their corresponding Python identifiers

    This is to prevent users having to think about escaping the default value for logging-format-style in the generated config file. Also our config parsing utilities don't quite support escaped values when it comes to choices detection, so this would have needed various hacks around that.

    Closes #2614

  What's New in Pylint 2.2.1?

Release date: 2018-11-27

•   Fix a crash caused by implicit-str-concat-in-sequence and multi-bytes characters.

    Closes #2610

  What's New in Pylint 2.2?

Release date: 2018-11-25

•   Consider range() objects for undefined-loop-variable leaking from iteration.

    Closes #2533

•   deprecated-method can use the attribute name for identifying a deprecated method Previously we were using the fully qualified name, which we still do, but the fully qualified name for some unittest deprecated aliases leads to a generic deprecation function. Instead on relying on that, we now also rely on the attribute name, which should solve some false positives. Closes #1653 Closes #1946

•   Fix compatibility with changes to stdlib tokenizer.

•   pylint is less eager to consume the whole line for pragmas

    Closes #2485

•   Obtain the correct number of CPUs for virtualized or containerized environments.

    Closes #2519

•   Change unbalanced-tuple-unpacking back to a warning. It used to be a warning until a couple of years ago, after it was promoted to an error. But the check might be suggesting the wrong thing in some cases, for instance when checking against sys.argv which cannot be known at static analysis time. Given it might rely on potential unknown data, it's best to have it as a warning. Closes #2522

•   Remove enumerate usage suggestion when defining __iter__ (C0200)

    Closes #2477

•   Emit too-many-starred-assignment only when the number of Starred nodes is per assignment elements

    Closes #2513

•   try-except-raise checker now handles multilevel inheritance hirerachy for exceptions correctly.

    Closes #2484

•   Add a new check, simplifiable-if-expression for expressions like True if cond else False.

    Closes #2487

•   too-few-public-methods is not reported for typing.NamedTuple

    Closes #2459

•   `too-few-public-methods is not reported for dataclasses created with options.

    Closes #2488

•   Remove wrong modules from 'bad-python3-import'.

    Closes #2453

•   The json reporter prints an empty list when no messages are emitted

    Closes #2446

•   Add a new check, duplicate-string-formatting-argument This new check is emitted whenever a duplicate string formatting argument is found. Closes #497

•   assignment-from-no-return is not emitted for coroutines.

    Closes #1715

•   Report format string type mismatches.

•   consider-using-ternary and simplified-boolean-expression no longer emit for sequence based checks

    Closes #2473

•   Handle AstroidSyntaxError when trying to import a module.

    Closes #2313

•   Allow __module__ to be redefined at a class level.

    Closes #2451

•   pylint used to emit an unused-variable error if unused import was found in the function. Now instead of unused-variable, unused-import is emitted.

    Closes #2421

•   Handle asyncio.coroutine when looking for not-an-iterable check.

    Closes #996

•   The locally-enabled check is gone.

    Closes #2442

•   Infer decorated methods when looking for method-hidden

    Closes #2369

•   Pick the latest value from the inferred values when looking for raising-non-exception

    Closes #2431

•   Extend the TYPE_CHECKING guard to TYPE_CHECKING name as well, not just the attribute

    Closes #2411

•   Ignore import x.y.z as z cases for checker useless-import-alias.

    Closes #2309

•   Fix false positive undefined-variable and used-before-assignment with nonlocal keyword usage.

    Closes #2049

•   Stop protected-access exception for missing class attributes

•   Don't emit assignment-from-no-return for decorated function nodes

    Closes #2385

•   unnecessary-pass is now also emitted when a function or class contains only docstring and pass statement.

    In Python, stubbed functions often have a body that contains just a single pass statement, indicating that the function doesn't do anything. However, a stubbed function can also have just a docstring, and function with a docstring and no body also does nothing.

    Closes #2208

•   duplicate-argument-name is emitted for more than one duplicate argument per function

    Closes #1712

•   Allow double indentation levels for more distinguishable indentations

    Closes #741

•   Consider tuples in exception handler for try-except-raise.

    Closes #2389

•   Fix astroid.ClassDef check in checkers.utils.is_subclass_of

•   Fix wildcard imports being ignored by the import checker

•   Fix external/internal distinction being broken in the import graph

•   Fix wildcard import check not skipping __init__.py

    Closes #2430

•   Add new option to logging checker, logging_format_style

•   Fix --ignore-imports to understand multi-line imports

    Closes #1422 Closes #2019

•   Add a new check 'implicit-str-concat-in-sequence' to spot string concatenation inside lists, sets & tuples.

•   literal-comparison is now emitted for 0 and 1 literals.

  What's New In Pylint 2.1

From pylint's beginning to pylint 2.14.0 included, we had a changelog that contained all nontrivial changes to Pylint, including changes that were not user facing, i.e. change that might interest you only if you're a developer working on pylint or pylint plugins or an open-source historian.

From pylint 1.6.0 to 2.14.0, on top of the full changelog there was also a summary of (mostly user facing) changes.

  Summary -- Release highlights

•   This release mostly includes fixes for bugs found after the launch of 2.0.

  New checkers

•   A new check was added, misplaced-format-function.

    This message is emitted when pylint detects that a format function is called on non str object. This can occur due to wrong placement of closing bracket, e.g

    print('value: {}').format(123) # bad
    print('value: {}'.format(123)) # good

  Other Changes

•   try-except-raise check was demoted from an error to a warning, as part of issue #2323.

•   Correctly handle the new name of the Python implementation of the abc module.

    In Python 3.7, the abc module has both a C implementation as well as a Python one, but the Python implementation has a different file name that what pylint was expecting, resulting in some checks getting confused.

•   Modules with __getattr__ are exempted by default from no-member

    There's no easy way to figure out if a module has a particular member when the said module uses __getattr__, which is a new addition to Python 3.7. Instead we assume the safe thing to do, in the same way we do for classes, and skip those modules from checking.

•   invalid name is no longer triggered for function and attribute names longer than 30 characters. The upper limit was removed completely.

•   Fix false-positive undefined-variable for self referential class name in lamdbas

•   no-else-return also specifies the type of the branch that is causing the error.

•   Fixed inconsistent behaviour for bad-continuation on first line of file.

•   Fixed a bug where pylint was not able to disable certain messages on the last line through the global disable option.

•   pylint no longer emits useless-return when it finds a single statement that is the return itself

    We still want to be explicit when a function is supposed to return an optional value; even though pass could still work, it's not explicit enough and the function might look like it's missing an implementation.

•   Fixed a bug where pylint was crashing when being unable to infer the value of an argument to next()

•   pylint no longer emit not-an-iterable when dealing with async iterators.

•   pylint gained the ability to specify a default docstring type for when the check cannot guess the type

    For this we added a --default-docstring-type command line option.

  Full changelog

  What's New in Pylint 2.1.1?

Release date: 2018-08-07

•   fix pylint crash due to misplaced-format-function not correctly handling class attribute.

    Closes #2384

•   Do not emit *-builtin for Python 3 builtin checks when the builtin is used inside a try-except

    Closes #2228

•   simplifiable-if-statement not emitted when dealing with subscripts

  What's New in Pylint 2.1?

Release date: 2018-08-01

•   trailing-comma-tuple gets emitted for yield statements as well.

    Closes #2363

•   Get only the arguments of the scope function for redefined-argument-from-local

    Closes #2364

•   Add a check misplaced-format-function which is emitted if format function is used on non str object.

    Closes #2200

•   chain.from_iterable no longer emits dict-{}-not-iterating when dealing with dict values and keys

•   Demote the try-except-raise message from an error to a warning (E0705 -> W0706)

    Closes #2323

•   Correctly handle the new name of the Python implementation of the abc module.

    Closes PyCQA/astroid#2288

•   Modules with __getattr__ are exempted by default from no-member

    There's no easy way to figure out if a module has a particular member when the said module uses __getattr__, which is a new addition to Python 3.7. Instead we assume the safe thing to do, in the same way we do for classes, and skip those modules from checking.

    Closes #2331

•   Fix a false positive invalid name message when method or attribute name is longer then 30 characters.

    Closes #2047

•   Include the type of the next branch in no-else-return

    Closes #2295

•   Fix inconsistent behaviour for bad-continuation on first line of file

    Closes #2281

•   Fix not being able to disable certain messages on the last line through the global disable option Closes #2278

•   Don't emit useless-return when we have a single statement that is the return itself

    We still want to be explicit when a function is supposed to return an optional value; even though pass could still work, it's not explicit enough and the function might look like it's missing an implementation.

    Closes #2300

•   Fix false-positive undefined-variable for self referential class name in lamdbas

    Closes #704

•   Don't crash when pylint is unable to infer the value of an argument to next()

    Closes #2316

•   Don't emit not-an-iterable when dealing with async iterators.

    But do emit it when using the usual iteration protocol against async iterators.

    Closes #2311

•   Can specify a default docstring type for when the check cannot guess the type

    Closes #1169

  What's New In Pylint 2.0

From pylint's beginning to pylint 2.14.0 included, we had a changelog that contained all nontrivial changes to Pylint, including changes that were not user facing, i.e. change that might interest you only if you're a developer working on pylint or pylint plugins or an open-source historian.

From pylint 1.6.0 to 2.14.0, on top of the full changelog there was also a summary of (mostly user facing) changes.

  Summary -- Release highlights

•   Dropped support for Python 2. This release will work only on Python 3.4+.

    If you need to use pylint with Python 2, you can use Pylint 1.9+. We'll continue to do bug releases until 2020, when Python 2 goes officially EOL. pylint will gain the ability to analyze Python 2 files, but some checks might not work as they will assume that their running environment is Python 2.

•   Given the dropping of Python 2, the Python 3 porting mode (enabled via --py3k) can now also run with Python 3.

    The porting mode used to be a no-op on Python 3, but most of the messages can now be emitted when the running interpreter is Python 3. The only messages that won't be emitted are those that rely on a particular syntax specific to Python 2, for instance print as a statement.

  New checkers

•   A new check was added, useless-object-inheritance.

    This refactoring message is emitted when pylint detects that a class inherits from object, which is redundant as in Python 3, every class implicitly inherits from object.

    class A(object):
        pass
    class A:    # better
        pass

•   A new check was added, comparison-with-callable.

    This refactoring message is emitted when pylint detects that a comparison with a callable was made, which might suggest that some parenthesis were omitted, resulting in potential unwanted behaviour.

    def foo():
        return None
    def goo():
        return None
    if foo == 786:  # bad
        pass
    if foo() == 786:    # good
        pass

•   A new check was added, chained-comparison.

    This refactoring message is emitted if a boolean operation can be simplified by chaining some of its operations. check below example:

    if a < b and b < c:
        pass
    if a < b < c:   # better
        pass

•   A new check was added, useless-import-alias.

    This refactoring message is emitted when an import alias does not rename the original package.

    import numpy as numpy # bad
    import numpy as np # good
    from collection import OrderedDict as OrderedDict # bad
    from collection import OrderedDict as ordered_dict # good

•   A new check was added, comparison-with-itself.

    This refactoring message is emitted when a variable is compared against itself.

    if variable == variable:  # bad
        pass

•   A new check was added, consider-using-in.

    This refactoring message is emitted when a variable is compared against multiple values concatenated by ors instead of using the faster, more idiomatic "in" check.

    if variable == 1 or variable == 2 or variable == 3:  # bad
        pass
    if variable in (1, 2, 3):  # good
        pass

•   A new check was added, consider-using-get.

    This refactoring message is emitted when manually checking if a key is in a dictionary and getting its value if it is (and optionally a default if not) instead of the more idiomatic dict.get.

    if 'key' in dictionary:  # bad
        variable = dictionary['key']
    else:
        variable = 'default'
    variable = dictionary.get('key', 'default')  # good

•   A new check was added, consider-using-join.

    This refactoring message is emitted when using a for loop over an iterable to join strings instead of the faster, less memory consuming and more idiomatic str.join(sequence).

    result = ''  # bad
    for number in ['1', '2', '3']:
        result += number
    result = ''.join(['1', '2', '3'])  # good

•   New useless-return message when function or method ends with a "return" or "return None" statement and this is the only return statement in the body.

•   New use-symbolic-message-instead message when a message is activated or deactivated by id instead of symbol. The use of symbol is more explicit and easier to remind.

•   A new check was added, consider-swap-variables.

    This refactoring message is emitted when using a temporary variable in order to swap the values of two variables instead of the shorter, more idiomatic approach with tuple-unpacking.

    Instead of a temporary variable, the one-line syntax with commas should be used.

    See this style guide document or the Pycon 2007 swap values presentation for details.

    temp = a  # the wrong way
    a = b
    b = temp
    a, b = b, a  # the right way

•   Two new checks, invalid-envvar-value and invalid-envvar-default, were added.

    The former is trigger whenever pylint detects that environment variable manipulation functions uses a different type than strings, while the latter is emitted whenever the said functions are using a default variable of different type than expected.

•   A new check was added, subprocess-popen-preexec-fn,

    This refactoring message is emitted when using the keyword argument preexec_fn when creating subprocess.Popen instances which may be unsafe when used in the presence of threads.

    See subprocess.Popen for full warning details.

•   New try-except-raise message when an except handler block has a bare raise statement as its first operator or the exception type being raised is the same as the one being handled.

•   New possibly-unused-variable check added. This is similar to unused-variable, the only difference is that it is emitted when we detect a locals() call in the scope of the unused variable. The locals() call could potentially use the said variable, by consuming all values that are present up to the point of the call. This new check allows to disable this error when the user intentionally uses locals() to consume everything.

    For instance, the following code will now trigger this new error:

    def func():
        some_value = some_call()
        return locals()

•   New unhashable-dict-key check added to detect dict lookups using unhashable keys such as lists or dicts.

•   New self-cls-assignment warning check added.

    This is warning if the first argument of an instance/ class method gets assigned

    class Foo(object):
        def foo(self, bar):
            self = bar

•   New verbose mode option --verbose to display of extra non-checker-related output. Disabled by default.

•   Two new checks were added for recommending dict and set comprehensions where possible.

    These two checks are going to flag the following examples:

    dict([(k, v) for (k, v) in ...]) # better as {k: v for k, v in ...}
    set([k for k in ...]) # better as {k for k in ...}

  Other Changes

•   A couple of performance improvements brought to astroid should make pylint should be a bit faster as well.

    We added a new flag, max_inferable_values on astroid.MANAGER for limitting the maximum amount of values that astroid can infer when inferring values. This change should improve the performance when dealing with large frameworks such as django. You can also control this behaviour with pylint --limit-inference-results

    We also rewrote how nodes_of_class and get_children methods operate which should result in a performance boost for a couple of checks.

•   Fix a false positive inconsistent-return-statements message when exception is raised inside an else statement.

•   Don't warn for missing-type-doc and/or missing-return-type-doc, if type annotations exist on the function signature for a parameter and/or return type.

•   Fix a false positive inconsistent-return-statements message when if statement is inside try/except.

•   Fix a false positive inconsistent-return-statements message when while loop are used.

•   Fix emission of false positive no-member message for class with "private" attributes whose name is mangled.

•   Fix unused-argument false positives with overshadowed variable in dictionary comprehension.

•   Fixing false positive inconsistent-return-statements when never returning functions are used (i.e such as sys.exit).

•   Fix false positive inconsistent-return-statements message when a function is defined under an if statement.

•   Fix false positive inconsistent-return-statements message by avoiding useless exception inference if the exception is not handled.

•   Fix false positive undefined-variable for lambda argument in class definitions

•   Suppress false-positive not-callable messages from certain staticmethod descriptors

•   Expand ignored-argument-names include starred arguments and keyword arguments

•   singleton-comparison will suggest better boolean conditions for negative conditions.

•   undefined-loop-variable takes in consideration non-empty iterred objects before emitting.

    For instance, if the loop iterable is not empty, this check will no longer be emitted.

•   Enum classes no longer trigger too-few-methods

•   Special methods now count towards too-few-methods, and are considered part of the public API. They are still not counted towards the number of methods for too-many-methods.

•   docparams extension allows abstract methods to document returns documentation even if the default implementation does not return something. They also no longer need to document raising a NotImplementedError.

•   Skip wildcard import check for __init__.py.

•   Don't warn 'useless-super-delegation' if the subclass method has different type annotations.

•   Don't warn that a global variable is unused if it is defined by an import

    def func():
        global sys
        import sys

•   Added basic support for postponed evaluation of function annotations.

    If pylint detects the corresponding from __future__ import annotations import, it will not emit used-before-assignment and undefined-variable in the cases triggered by the annotations.

    More details on the postponed evaluation of annotations can be read in PEP 563.

•   A new command line option was added, --exit-zero, for the use of continuous integration scripts which abort if a command returns a non-zero status code. If the option is specified, and Pylint runs successfully, it will exit with 0 regardless of the number of lint issues detected.

    Configuration errors, parse errors, and calling Pylint with invalid command-line options all still return a non-zero error code, even if --exit-zero is specified.

•   Don't emit unused-import anymore for typing imports used in type comments. For instance, in the following example pylint used to complain that Any and List are not used, while they should be considered used by a type checker.

    from typing import Any, List
    a = 1 # type: List[Any]

•   Fix false positive line-too-long for commented lines at the end of module

•   Fix emitting useless-super-delegation when changing the default value of keyword arguments.

•   Support typing.TYPE_CHECKING for unused-import errors

    When modules are imported under typing.TYPE_CHECKING guard, pylint will no longer emit unused-import.

•   Fix false positive unused-variable in lambda default arguments

•   assignment-from-no-return considers methods as well as functions.

    If you have a method that doesn't return a value, but later on you assign a value to a function call to that method (so basically it will be None), then pylint is going to emit an assignment-from-no-return error.

•   A new flag was added, --ignore-none which controls the no-member behaviour with respect to None values.

    Previously pylint was not emitting no-member if it inferred that the owner of an attribute access is a None value. In some cases, this might actually cause bugs, so if you want to check for None values as well, pass --ignore-none=n to pylint.

•   Fix false-positive bad-continuation for with statements

•   Fix false-positive bad-whitespace message for typing annoatations with ellipses in them

•   Fix false-positive undefined-variable for nested lambdas

  Full changelog

  What's New in Pylint 2.0?

Release date: 2018-07-15

•   try-except-raise should not be emitted if there are any parent exception class handlers.

    Closes #2284

•   trailing-comma-tuple can be emitted for return statements as well.

    Closes #2269

•   Fix a false positive inconsistent-return-statements message when exception is raised inside an else statement.

    Closes #1782

•   ImportFrom nodes correctly use the full name for the import sorting checks.

    Closes #2181

•   [].extend and similar builtin operations don't emit dict-*-not-iterating with the Python 3 porting checker

    Closes #2187

•   Add a check consider-using-dict-comprehension which is emitted if for dict initialization the old style with list comprehensions is used.

•   Add a check consider-using-set-comprehension which is emitted if for set initialization the old style with list comprehensions is used.

•   logging-not-lazy is emitted whenever pylint infers that a string is built with addition

    Closes #2193

•   Add a check chained-comparison which is emitted if a boolean operation can be simplified by chaining some of its operations. e.g "a < b and b < c", can be simplified as "a < b < c".

    Closes #2032

•   Add a check consider-using-in for comparisons of a variable against multiple values with "==" and "or"s instead of checking if the variable is contained "in" a tuple of those values.

•   in is considered iterating context for some of the Python 3 porting checkers

    Closes #2186

•   Add --ignore-none flag to control if pylint should warn about no-member where the owner is None

•   Fix a false positive related to too-many-arguments and bounded __get__ methods

    Closes #2172

•   mcs as the first parameter of metaclass's __new__ method was replaced by cls

    Closes #2028

•   assignment-from-no-return considers methods as well.

    Closes #2081

•   Support typing.TYPE_CHECKING for unused-import errors

    Closes #1948

•   Inferred classes at a function level no longer emit invalid-name when they don't respect the variable regular expression

    Closes #1049

•   Added basic support for postponed evaluation of function annotations.

    Closes #2069

•   Fix a bug with missing-kwoa and variadics parameters

    Closes #1111

•   simplifiable-if-statement takes in account only when assigning to same targets

    Closes #1984

•   Make len-as-condition test more cases, such as len() < 1 or len <= 0

•   Fix false-positive line-too-long message emission for commented line at the end of a module

    Closes #1950

•   Fix false-positive bad-continuation for with statements

    Closes #461

•   Don't warn about stop-iteration-return when using next() over itertools.count

    Closes #2158

•   Add a check consider-using-get for unidiomatic usage of value/default-retrieval for a key from a dictionary

    Closes #2076

•   invalid-slice-index is not emitted when the slice is used as index for a complex object.

    We only use a handful of known objects (list, set and friends) to figure out if we should emit invalid-slice-index when the slice is used to subscript an object.

•   Don't emit unused-import anymore for typing imports used in type comments.

•   Add a new check 'useless-import-alias'.

    Closes #2052

•   Add comparison-with-callable to warn for comparison with bare callable, without calling it.

    Closes #2082

•   Don't warn for missing-type-doc and/or missing-return-type-doc, if type annotations exist on the function signature for a parameter and/or return type.

    Closes #2083

•   Add --exit-zero option for continuous integration scripts to more easily call Pylint in environments that abort when a program returns a non-zero (error) status code.

    Closes #2042

•   Warn if the first argument of an instance/ class method gets assigned

    Closes #977

•   New check comparison-with-itself to check comparison between same value.

    Closes #2051

•   Add a new warning, 'logging-fstring-interpolation', emitted when f-string is used within logging function calls.

    Closes #1998

•   Don't show 'useless-super-delegation' if the subclass method has different type annotations.

    Closes #1923

•   Add unhashable-dict-key check.

    Closes #586

•   Don't warn that a global variable is unused if it is defined by an import

    Closes #1453

•   Skip wildcard import check for __init__.py.

    Closes #2026

•   The Python 3 porting mode can now run with Python 3 as well.

•   too-few-public-methods is not emitted for dataclasses.

    Closes #1793

•   New verbose mode option, enabled with --verbose command line flag, to display of extra non-checker-related output. It is disabled by default.

    Closes #1863

•   undefined-loop-variable takes in consideration non-empty iterred objects before emitting

    Closes #2039

•   Add support for numpydoc optional return value names.

    Closes #2030

•   singleton-comparison accounts for negative checks

    Closes #2037

•   Add a check consider-using-in for comparisons of a variable against multiple values with "==" and "or"s instead of checking if the variable is contained "in" a tuple of those values.

    Closes #1977

•   defaultdict and subclasses of dict are now handled for dict-iter-* checks

    Closes #2005

•   logging-format-interpolation also emits when f-strings are used instead of % syntax.

    Closes #1788

•   Don't trigger misplaced-bare-raise when the raise is in a finally clause

    Closes #1924

•   Add a new check, possibly-unused-variable.

    This is similar to unused-variable, the only difference is that it is emitted when we detect a locals() call in the scope of the unused variable. The locals() call could potentially use the said variable, by consuming all values that are present up to the point of the call. This new check allows to disable this error when the user intentionally uses locals() to consume everything.

    Closes #1909.

•   no-else-return accounts for multiple cases The check was a bit overrestrictive because we were checking for return nodes in the .orelse node. At that point though the if statement can be refactored to not have the orelse. This improves the detection of other cases, for instance it now detects TryExcept nodes that are part of the .else branch.

    Closes #1852

•   Added two new checks, invalid-envvar-value and invalid-envvar-default.

    The former is trigger whenever pylint detects that environment variable manipulation functions uses a different type than strings, while the latter is emitted whenever the said functions are using a default variable of different type than expected.

•   Add a check consider-using-join for concatenation of strings using str.join(sequence)

    Closes #1952

•   Add a check consider-swap-variables for swapping variables with tuple unpacking

    Closes #1922

•   Add new checker try-except-raise that warns the user if an except handler block has a raise statement as its first operator. The warning is shown when there is a bare raise statement, effectively re-raising the exception that was caught or the type of the exception being raised is the same as the one being handled.

•   Don't crash on invalid strings when checking for logging-format-interpolation

    Closes #1944

•   Exempt __doc__ from triggering a redefined-builtin

    __doc__ can be used to specify a docstring for a module without passing it as a first-statement string.

•   Fix false positive bad-whitespace from function arguments with default values and annotations

    Closes #1831

•   Fix stop-iteration-return false positive when next builtin has a default value in a generator

    Closes #1830

•   Fix emission of false positive no-member message for class with "private" attributes whose name is mangled.

    Closes #1643

•   Fixed a crash which occurred when Uninferable wasn't properly handled in stop-iteration-return

    Closes #1779

•   Use the proper node to get the name for redefined functions (#1792)

    Closes #1774

•   Don't crash when encountering bare raises while checking inconsistent returns

    Closes #1773

•   Fix a false positive inconsistent-return-statements message when if statement is inside try/except.

    Closes #1770

•   Fix a false positive inconsistent-return-statements message when while loop are used.

    Closes #1772

•   Correct column number for whitespace conventions.

    Previously the column was stuck at 0

    Closes #1649

•   Fix unused-argument false positives with overshadowed variable in dictionary comprehension.

    Closes #1731

•   Fix false positive inconsistent-return-statements message when never returning functions are used (i.e sys.exit for example).

    Closes #1771

•   Fix error when checking if function is exception, as in bad-exception-context.

•   Fix false positive inconsistent-return-statements message when a function is defined under an if statement.

    Closes #1794

•   New useless-return message when function or method ends with a "return" or "return None" statement and this is the only return statement in the body.

•   Fix false positive inconsistent-return-statements message by avoiding useless exception inference if the exception is not handled.

    Closes #1794 (second part)

•   Fix bad thread instantiation check when target function is provided in args.

    Closes #1840

•   Fixed false positive when a numpy Attributes section follows a Parameters section

    Closes #1867

•   Fix incorrect file path when file absolute path contains multiple path_strip_prefix strings.

    Closes #1120

•   Fix false positive undefined-variable for lambda argument in class definitions

    Closes #1824

•   Add of a new checker that warns the user if some messages are enabled or disabled by id instead of symbol.

    Closes #1599

•   Suppress false-positive not-callable messages from certain staticmethod descriptors

    Closes #1699

•   Fix indentation handling with tabs

    Closes #1148

•   Fix false-positive bad-continuation error

    Closes #638

•   Fix false positive unused-variable in lambda default arguments

    Closes #1921 Closes #1552 Closes #1099 Closes #210

•   Updated the default report format to include paths that can be clicked on in some terminals (e.g. iTerm).

•   Fix inline def behavior with too-many-statements checker

    Closes #1978

•   Fix KeyError raised when using docparams and NotImplementedError is documented.

    Closes #2102

•   Fix 'method-hidden' raised when assigning to a property or data descriptor.

•   Fix emitting useless-super-delegation when changing the default value of keyword arguments.

    Closes #2022

•   Expand ignored-argument-names include starred arguments and keyword arguments

    Closes #2214

•   Fix false-positive undefined-variable in nested lambda

    Closes #760

•   Fix false-positive bad-whitespace message for typing annoatations with ellipses in them

    Close 1992

•   Broke down "missing-docstrings" between "module", "class" and "function"

    For this to work we had to make multiple messages with the same old name possible.

    Closes #1164

  1.x

From pylint's beginning to pylint 2.14.0 included, we had a changelog that contained all nontrivial changes to Pylint, including changes that were not user facing, i.e. change that might interest you only if you're a developer working on pylint or pylint plugins or an open-source historian.

From pylint 1.6.0 to 2.14.0, on top of the full changelog there was also a summary of (mostly user facing) changes.

  What's New In Pylint 1.9

From pylint's beginning to pylint 2.14.0 included, we had a changelog that contained all nontrivial changes to Pylint, including changes that were not user facing, i.e. change that might interest you only if you're a developer working on pylint or pylint plugins or an open-source historian.

From pylint 1.6.0 to 2.14.0, on top of the full changelog there was also a summary of (mostly user facing) changes.

  Summary -- Release highlights

•   None so far

  New checkers

•   A new Python 3 checker was added to warn about the removed operator.div function.

•   A new Python 3 checker was added to warn about accessing functions that have been moved from the urllib module in corresponding subpackages, such as urllib.request.

    from urllib import urlencode

    Instead the previous code should use urllib.parse or six.moves to import a module in a Python 2 and 3 compatible fashion:

    from six.moves.urllib.parse import urlencode

    To have this working on Python 3 as well, please use the six library:

    six.reraise(Exception, "value", tb)

•   A new check was added to warn about using unicode raw string literals. This is a syntax error in Python 3:

    a = ur'...'

•   Added a new deprecated-sys-function check, emitted when accessing removed sys members.

•   Added xreadlines-attribute check, emitted when the xreadlines() attribute is accessed on a file object.

•   Added two new Python 3 porting checks, exception-escape and comprehension-escape

    These two are emitted whenever pylint detects that a variable defined in the said blocks is used outside of the given block. On Python 3 these values are deleted.

    try:
      1/0
    except ZeroDivisionError as exc:
       ...
    print(exc) # This will raise a NameError on Python 3
    [i for i in some_iterator if some_condition(i)]
    print(i) # This will raise a NameError on Python 3

  Other Changes

•   defaultdict and subclasses of dict are now handled for dict-iter-* checks. That means that the following code will now emit warnings for when iteritems and friends are accessed:

    some_dict = defaultdict(list)
    ...
    some_dict.iterkeys()

•   Enum classes no longer trigger too-few-methods

•   Special methods now count towards too-few-methods, and are considered part of the public API. They are still not counted towards the number of methods for too-many-methods.

•   docparams allows abstract methods to document returns documentation even if the default implementation does not return something. They also no longer need to document raising a NotImplementedError.

  Full changelog

  What's New in Pylint 1.9?

Release date: 2018-05-15

•   Added two new Python 3 porting checks, exception-escape and comprehension-escape

    These two are emitted whenever pylint detects that a variable defined in the said blocks is used outside of the given block. On Python 3 these values are deleted.

•   Added a new deprecated-sys-function, emitted when accessing removed sys members.

•   Added xreadlines-attribute, emitted when the xreadlines() attribute is accessed.

•   The Python 3 porting mode can now run with Python 3 as well.

•   docparams extension allows abstract methods to document what overriding implementations should return, and to raise NotImplementedError without documenting it.

    Closes #2044

•   Special methods do not count towards too-few-methods, and are considered part of the public API.

•   Enum classes do not trigger too-few-methods

    Closes #605

•   Added a new Python 2/3 check for accessing operator.div, which is removed in Python 3

    Closes #1936

•   Added a new Python 2/3 check for accessing removed urllib functions

    Closes #1997

  What's New In Pylint 1.8

From pylint's beginning to pylint 2.14.0 included, we had a changelog that contained all nontrivial changes to Pylint, including changes that were not user facing, i.e. change that might interest you only if you're a developer working on pylint or pylint plugins or an open-source historian.

From pylint 1.6.0 to 2.14.0, on top of the full changelog there was also a summary of (mostly user facing) changes.

  Summary -- Release highlights

•   None so far

  New checkers

•   A new check was added, shallow-copy-environ.

    This warning message is emitted when shallow copy of os.environ is created. Shallow copy of os.environ doesn't work as people may expect. os.environ is not a dict object but rather a proxy object, so any changes made on copy may have unexpected effects on os.environ

    Instead of copy.copy(os.environ) method os.environ.copy() should be used.

    See https://bugs.python.org/issue15373 for details.

    import copy
    import os
    wrong_env_copy = copy.copy(os.environ)  # will emit pylint warning
    wrong_env_copy['ENV_VAR'] = 'new_value'  # changes os.environ
    assert os.environ['ENV_VAR'] == 'new_value'
    good_env_copy = dict(os.environ)  # the right way
    good_env_copy['ENV_VAR'] = 'different_value'  # doesn't change os.environ
    assert os.environ['ENV_VAR'] == 'new_value'

•   A new check was added, keyword-arg-before-vararg.

    This warning message is emitted when a function is defined with a keyword argument appearing before variable-length positional arguments (*args). This may lead to args list getting modified if keyword argument's value is not provided in the function call assuming it will take default value provided in the definition.

    def foo(a, b=3, *args):
        print(a, b, args)
    # Case1: a=0, b=2, args=(4,5)
    foo(0,2,4,5) # 0 2 (4,5) ==> Observed values are same as expected values
    # Case2: a=0, b=<default_value>, args=(4,5)
    foo(0,4,5) # 0 4 (5,) ==> args list got modified as well as the observed value of b
    # Case3: Syntax Error if tried as follows
    foo(0,b=2,4,5) # syntax error

•   A new check was added, simplify-boolean-expression.

    This message is emitted when consider-using-ternary check would emit not equivalent code, due to truthy element being falsy in boolean context.

    value = condition and False or other_value

    This flawed construct may be simplified to:

    value = other_value

•   A new check was added, bad-thread-instantiation.

    This message is emitted when the threading.Thread class does not receive the target argument, but receives just one argument, which is by default the group parameter.

    In the following example, the instantiation will fail, which is definitely not desired:

    import threading
    threading.Thread(lambda: print(1)) # Oups, this is the group parameter

•   A new Python 3 checker was added to warn about accessing functions that have been removed from the itertools module izip, imap, iflter, izip_longest, and ifilterfalse.

    from itertools import izip
    print(list(izip([1, 2], [3])))

    Instead use six.moves to import a Python 2 and Python 3 compatible function:

    from six.moves import zip
    print(list(zip([1, 2], [3])))

•   A new Python 3 checker was added to warn about accessing deprecated fields from the types module like ListType or IntType

    from types import ListType
    print(isinstance([], ListType))

    Instead use the declarations in the builtin namespace:

    print(isinstance([], list))

•   A new Python 3 checker was added to warn about declaring a next method that would have implemented the Iterator protocol in Python 2 but is now a normal method in Python 3.

    class Foo(object):
        def next(self):
            return 42

    Instead implement a __next__ method and use six.Iterator as a base class or alias next to __next__:

    class Foo(object):
        def __next__(self):
            return 42
        next = __next__

•   Three new Python 3 checkers were added to warn about using dictionary methods in non-iterating contexts.

    For example, the following are returning iterators in Python 3:

    .. code-block:: python
    d = {} d.keys()[0] d.items()[0] d.values() + d.keys()

•   A new Python 3 porting check was added, non-ascii-bytes-literals

    This message is emitted whenever we detect that a bytes string contain non-ASCII characters, which results in a SyntaxError on Python 3.

•   A new warning, raising-format-tuple, will catch situations where the intent was likely raising an exception with a formatted message string, but the actual code did omit the formatting and instead passes template string and value parameters as separate arguments to the exception constructor. So it detects things like

    raise SomeError('message about %s', foo)
    raise SomeError('message about {}', foo)

    which likely were meant instead as

    raise SomeError('message about %s' % foo)
    raise SomeError('message about {}'.format(foo))

    This warning can be ignored on projects which deliberately use lazy formatting of messages in all user-facing exception handlers.

•   Following the recommendations of PEP479 ,a new Python 3.0 checker was added to warn about raising a StopIteration inside a generator. Raising a StopIteration inside a generator may be due a direct call to raise StopIteration:

    def gen_stopiter():
        yield 1
        yield 2
        yield 3
        raise StopIteration

    Instead use a simple return statement

    def gen_stopiter():
        yield 1
        yield 2
        yield 3
        return

    Raising a StopIteration may also be due to the call to next function with a generator as argument:

    def gen_next_raises_stopiter():
        g = gen_ok()
        while True:
            yield next(g)

    In this case, surround the call to next with a try/except block:

    def gen_next_raises_stopiter():
        g = gen_ok()
        while True:
            try:
                yield next(g)
            except StopIteration:
                return

•   The check about raising a StopIteration inside a generator is also valid if the exception raised inherit from StopIteration.

    Closes #1385

•   A new Python checker was added to warn about using a + operator inside call of logging methods when one of the operands is a literal string:

    import logging
    var = "123"
    logging.log(logging.INFO, "Var: " + var)

    Instead use formatted string and positional arguments :

    import logging
    var = "123"
    logging.log(logging.INFO, "Var: %s", var)

•   A new Python checker was added to warn about inconsistent-return-statements. A function or a method has inconsistent return statements if it returns both explicit and implicit values :

    def mix_implicit_explicit_returns(arg):
        if arg < 10:
            return True
        elif arg < 20:
            return

    According to PEP8, if any return statement returns an expression, any return statements where no value is returned should explicitly state this as return None, and an explicit return statement should be present at the end of the function (if reachable). Thus, the previous function should be written:

    def mix_implicit_explicit_returns(arg):
        if arg < 10:
            return True
        elif arg < 20:
            return None

    Closes #1267

  Other Changes

•   Fixing u'' string in superfluous-parens message.

•   Configuration options of invalid name checker are significantly redesigned. Predefined rules for common naming styles were introduced. For typical setups, user friendly options like --function-naming-style=camelCase may be used in place of hand-written regular expressions. Default linter config enforce PEP8-compatible naming style. See documentation for details.

•   Raise meaningful exception in case of invalid reporter class (output format) being selected.

•   The docparams extension now allows a property docstring to document both the property and the setter. Therefore setters can also have no docstring.

•   The docparams extension now understands property type syntax.

    class Foo(object):
        @property
        def foo(self):
            """My Sphinx style docstring description.
            :type: int
            """
            return 10

    class Foo(object):
        @property
        def foo(self):
            """int: My Numpy and Google docstring style description."""
            return 10

•   In case of --output-format=json, the dictionary returned holds a new key-value pair. The key is message-id and the value the message id.

•   Spelling checker has a new configuration parameter max-spelling-suggestions, which affects maximum count of suggestions included in emitted message.

•   The invalid-name check contains the name of the template that caused the failure.

    For the given code, pylint used to emit invalid-name in the form Invalid constant name var, without offering any context why var is not such a good name.

    With this change, it is now more clear what should be improved for a name to be accepted according to its corresponding template.

•   New configuration flag, suggestion-mode was introduced. When enabled, pylint would attempt to emit user-friendly suggestions instead of spurious errors for some known false-positive scenarios. Flag is enabled by default.

•   superfluous-parens is no longer wrongly emitted for logical statements involving in operator (see example below for what used to be false-positive).

    foo = None
    if 'bar' in (foo or {}):
      pass

•   Redefinition of dummy function is now possible. function-redefined message won't be emitted anymore when dummy functions are redefined.

•   missing-param-doc and missing-type-doc are no longer emitted when Args and Keyword Args are mixed in Google docstring.

•   Fix of false positive useless-super-delegation message when parameters default values are different from those used in the base class.

•   Fix of false positive useless-else-on-loop message when break statements are deeply nested inside loop.

•   The Python 3 porting checker no longer emits multiple no-absolute-import per file.

•   The Python 3 porting checker respects disabled checkers found in the config file.

•   Modules, classes, or methods consist of compound statements that exceed the docstring-min-length are now correctly emitting missing-docstring

•   Fix no wrong-import-order message emitted on ordering of first and third party libraries. With this fix, pylint distinguishes first and third party modules when checking import order.

•   Fix the ignored pylint disable=fixme directives for comments following the last statement in a file.

•   Fix line-too-long message deactivated by wrong disable directive. The directive disable=fixme doesn't deactivate anymore the emission of line-too-long message for long commented lines.

•   If the rcfile specified on the command line doesn't exist, then an IOError exception is raised.

•   Fix the wrong scope of disable= directive after a commented line. For example when a disable=line-too-long directive is at the end of a long commented line, it no longer disables the emission of line-too-long message for lines that follow.

  Full changelog

  What's New in Pylint 1.8.1?

Release date: 2017-12-15

•   Wrong version number in __pkginfo__.

  What's New in Pylint 1.8?

Release date: 2017-12-15

•   Respect disable=... in config file when running with --py3k.

•   New warning shallow-copy-environ added

    Shallow copy of os.environ doesn't work as people may expect. os.environ is not a dict object but rather a proxy object, so any changes made on copy may have unexpected effects on os.environ

    Instead of copy.copy(os.environ) method os.environ.copy() should be used.

    See https://bugs.python.org/issue15373 for details.

    Closes #1301

•   Do not display no-absolute-import warning multiple times per file.

•

trailing-comma-tuple refactor check now extends to assignment with
    more than one element (such as lists)

    Closes #1713

•   Fixing u'' string in superfluous-parens message

    Closes #1420

•   abstract-class-instantiated is now emitted for all inference paths.

    Closes #1673

•   Add set of predefined naming style to ease configuration of checking naming conventions.

    Closes #1013

•   Added a new check, keyword-arg-before-vararg

    This is emitted for function definitions in which keyword arguments are placed before variable positional arguments (*args).

    This may lead to args list getting modified if keyword argument's value is not provided in the function call assuming it will take default value provided in the definition.

•   The invalid-name check contains the name of the template that caused the failure

    Closes #1176

•   Using the -j flag won't start more child linters than needed.

    Closes #1614

•   Fix a false positive with bad-python3-import on relative imports

    Closes #1608

•   Added a new Python 3 check, non-ascii-bytes-literals

    Closes #1545

•   Added a couple of new Python 3 checks for accessing dict methods in non-iterable context

•   Protocol checks (not-a-mapping, not-an-iterable and co.) aren't emitted on classes with dynamic getattr

•   Added a new warning, 'bad-thread-instantiation'

    This message is emitted when the threading.Thread class does not receive the target argument, but receives just one argument, which is by default the group parameter.

    Closes #1327

•   In non-quiet mode, absolute path of used config file is logged to standard error.

    Closes #1519

•   Raise meaningful exception for invalid reporter class being selected

    When unknown reporter class will be selected as Pylint reporter, meaningful error message would be raised instead of bare ImportError or AttributeError related to module or reporter class being not found.

    Closes #1388

•   Added a new Python 3 check for accessing removed functions from itertools like izip or ifilterfalse

•   Added a new Python 3 check for accessing removed fields from the types module like UnicodeType or XRangeType

•   Added a new Python 3 check for declaring a method next that would have been treated as an iterator in Python 2 but a normal function in Python 3.

•   Added a new key-value pair in json output. The key is message-id and the value is the message id.

    Closes #1512

•   Added a new Python 3.0 check for raising a StopIteration inside a generator. The check about raising a StopIteration inside a generator is also valid if the exception raised inherit from StopIteration.

    Closes #1385

•   Added a new warning, raising-format-tuple, to detect multi-argument exception construction instead of message string formatting.

•   Added a new check for method of logging module that concatenate string via + operator

    Closes #1479

•   Added parameter for limiting number of suggestions in spellchecking checkers

•   Fix a corner-case in consider-using-ternary checker.

    When object A used in X and A or B was falsy in boolean context, Pylint incorrectly emitted non-equivalent ternary-based suggestion. After a change message is correctly not emitted for this case.

    Closes #1559

•   Added suggestion-mode configuration flag. When flag is enabled, informational message is emitted instead of cryptic error message for attributes accessed on c-extensions.

    Closes #1466

•   Fix a false positive useless-super-delegation message when parameters default values are different from those used in the base class.

    Closes #1085

•   Disabling 'wrong-import-order', 'wrong-import-position', or 'ungrouped-imports' for a single line now prevents that line from triggering violations on subsequent lines.

    Closes #1336

•   Added a new Python check for inconsistent return statements inside method or function.

    Closes #1267

•   Fix superfluous-parens false positive related to handling logical statements involving in operator.

    Closes #574

•   function-redefined message is no longer emitted for functions and methods which names matches dummy variable name regular expression.

    Closes #1369

•   Fix missing-param-doc and missing-type-doc false positives when mixing Args and Keyword Args in Google docstring.

    Closes #1409

•   Fix missing-docstring false negatives when modules, classes, or methods consist of compound statements that exceed the docstring-min-length

•   Fix useless-else-on-loop false positives when break statements are deeply nested inside loop.

    Closes #1661

•   Fix no wrong-import-order message emitted on ordering of first and third party libraries. With this fix, pylint distinguishes third and first party modules when checking import order.

    Closes #1702

•   Fix pylint disable=fixme directives ignored for comments following the last statement in a file.

    Closes #1681

•   Fix line-too-long message deactivated by wrong disable directive. The directive disable=fixme doesn't deactivate anymore the emission of line-too-long message for long commented lines.

    Closes #1741

•   If the rcfile specified on the command line doesn't exist, then an IOError exception is raised.

    Closes #1747

•   Fix the wrong scope of the disable= directive after a commented line. For example when a disable=line-too-long directive is at the end of a long commented line, it no longer disables the emission of line-too-long message for lines that follow.

    Closes #1742

  What's New In Pylint 1.7

From pylint's beginning to pylint 2.14.0 included, we had a changelog that contained all nontrivial changes to Pylint, including changes that were not user facing, i.e. change that might interest you only if you're a developer working on pylint or pylint plugins or an open-source historian.

From pylint 1.6.0 to 2.14.0, on top of the full changelog there was also a summary of (mostly user facing) changes.

  Summary -- Release highlights

  New checkers

•   single-string-used-for-slots check was added, which is used whenever a class is using a single string as a slot value. While this is technically not a problem per se, it might trip users when manipulating the slots value as an iterable, which would in turn iterate over characters of the slot value. In order to be more straight-forward, always try to use a container such as a list or a tuple for defining slot values.

•   We added a new check, literal-comparison, which is used whenever pylint can detect a comparison to a literal. This is usually not what we want and, potentially, error prone. For instance, in the given example, the first string comparison returns true, since smaller strings are interned by the interpreter, while for larger ones, it will return False:

    mystring = "ok"
    if mystring is "ok": # Returns true
       ...
    mystring = "a" * 1000
    if mystring is ("a" * 1000): # This will return False
       ...

    Instead of using the is operator, you should use the == operator for this use case.

•   We added a new refactoring message, consider-merging-isinstance, which is emitted whenever we can detect that consecutive isinstance calls can be merged together. For instance, in this example, we can merge the first two isinstance calls:

    # $ cat a.py
    if isinstance(x, int) or isinstance(x, float):
        pass
    if isinstance(x, (int, float)) or isinstance(x, str):
        pass
    # $ pylint a.py
    # R:  1, 0: Consider merging these isinstance calls to isinstance(x, (float, int)) (consider-merging-isinstance)
    # R:  3, 0: Consider merging these isinstance calls to isinstance(x, (int, float, str)) (consider-merging-isinstance)

•   A new error check was added, invalid-metaclass, which is used whenever pylint can detect that a given class is using a metaclass which is invalid for the purpose of the class. This usually might indicate a problem in the code, rather than something done on purpose.

    # Needs to inherit from *type* in order to be valid
    class SomeClass(object):
        ...
    class MyClass(metaclass=SomeClass):
        pass

•   A new warning was added, useless-super-delegation, which is used whenever we can detect that an overridden method is useless, relying on super() delegation to do the same thing as another method from the MRO.

    For instance, in this example, the first two methods are useless, since they do the exact same thing as the methods from the base classes, while the next two methods are not, since they do some extra operations with the passed arguments.

    class Impl(Base):
        def __init__(self, param1, param2):
            super(Impl, self).__init__(param1, param2)
        def useless(self, first, second):
            return super(Impl, self).useless(first, second)
        def not_useless(self, first, **kwargs):
            debug = kwargs.pop('debug', False)
            if debug:
                ...
            return super(Impl, self).not_useless(first, **kwargs)
        def not_useless_1(self, first, *args):
            return super(Impl, self).not_useless_1(first + some_value, *args)

•   A new warning was added, len-as-condition, which is used whenever we detect that a condition uses len(SEQUENCE) incorrectly. Instead one could use if SEQUENCE or if not SEQUENCE.

    For instance, all of the examples below:

    if len(S):
      pass
    if not len(S):
      pass
    if len(S) > 0:
      pass
    if len(S) != 0:
      pass
    if len(S) == 0:
      pass

    can be written in a more natural way:

    if S:
      pass
    if not S:
      pass

    See https://peps.python.org/pep-0008/#programming-recommendations for more information.

•   A new extension was added, emptystring.py which detects whenever we detect comparisons to empty string constants. This extension is disabled by default. For instance, the examples below:

    if S != "":
      pass
    if S == '':
      pass

    can be written in a more natural way:

    if S:
      pass
    if not S:
      pass

    An exception to this is when empty string is an allowed value whose meaning is treated differently than None. For example the meaning could be user selected no additional options vs. user has not made their selection yet!

    You can activate this checker by adding the line:

    load-plugins=pylint.extensions.emptystring

    to the MAIN section of your .pylintrc or using the command:

    $ pylint a.py --load-plugins=pylint.extensions.emptystring

•   A new extension was added, comparetozero.py which detects whenever we compare integers to zero. This extension is disabled by default. For instance, the examples below:

    if X != 0:
      pass
    if X == 0:
      pass

    can be written in a more natural way:

    if X:
      pass
    if not X:
      pass

    An exception to this is when zero is an allowed value whose meaning is treated differently than None. For example the meaning could be None means no limit, while 0 means the limit it zero!

    You can activate this checker by adding the line:

    load-plugins=pylint.extensions.comparetozero

    to the MAIN section of your .pylintrc or using the command:

    $ pylint a.py --load-plugins=pylint.extensions.comparetozero

•   We've added new error conditions for bad-super-call which now detect the usage of super(type(self), self) and super(self.__class__, self) patterns. These can lead to recursion loop in derived classes. The problem is visible only if you override a class that uses these incorrect invocations of super().

    For instance, Derived.__init__() will correctly call Base.__init__. At this point type(self) will be equal to Derived and the call again goes to Base.__init__ and we enter a recursion loop.

    class Base(object):
        def __init__(self, param1, param2):
            super(type(self), self).__init__(param1, param2)
    class Derived(Base):
        def __init__(self, param1, param2):
            super(Derived, self).__init__(param1, param2)

•   The warnings missing-returns-doc and missing-yields-doc have each been replaced with two new warnings - missing-[return|yield]-doc and missing-[return|yield]-type-doc. Having these as separate warnings allows the user to choose whether their documentation style requires text descriptions of function return/yield, specification of return/yield types, or both.

    # This will raise missing-return-type-doc but not missing-return-doc
    def my_sphinx_style_func(self):
        """This is a Sphinx-style docstring.
        :returns: Always False
        """
        return False
    # This will raise missing-return-doc but not missing-return-type-doc
    def my_google_style_func(self):
        """This is a Google-style docstring.
        Returns:
            bool:
        """
        return False

•   A new refactoring check was added, redefined-argument-from-local, which is emitted when pylint can detect than a function argument is redefined locally in some potential error prone cases. For instance, in the following piece of code, we have a bug, since the check will never return True, given the fact that we are comparing the same object to its attributes.

    def test(resource):
        for resource in resources:
            # The ``for`` is reusing ``resource``, which means that the following
            # ``resource`` is not what we wanted to check against.
            if resource.resource_type == resource:
               call_resource(resource)

    Other places where this check looks are with statement name bindings and except handler's name binding.

•   A new refactoring check was added, no-else-return, which is emitted when pylint encounters an else following a chain of ifs, all of them containing a return statement.

    def foo1(x, y, z):
        if x:
            return y
        else:  # This is unnecessary here.
            return z

    We could fix it deleting the else statement.

    def foo1(x, y, z):
        if x:
            return y
        return z

•   A new Python 3 check was added, eq-without-hash, which enforces classes that implement __eq__ also implement __hash__. The behavior around classes which implement __eq__ but not __hash__ changed in Python 3; in Python 2 such classes would get object.__hash__ as their default implementation. In Python 3, aforementioned classes get None as their implementation thus making them unhashable.

    class JustEq(object):
       def __init__(self, x):
         self.x = x
       def __eq__(self, other):
         return self.x == other.x
    class Neither(object):
      def __init__(self, x):
        self.x = x
    class HashAndEq(object):
       def __init__(self, x):
         self.x = x
       def __eq__(self, other):
         return self.x == other.x
       def __hash__(self):
         return hash(self.x)
    {Neither(1), Neither(2)}  # OK in Python 2 and Python 3
    {HashAndEq(1), HashAndEq(2)}  # OK in Python 2 and Python 3
    {JustEq(1), JustEq(2)}  # Works in Python 2, throws in Python 3

    In general, this is a poor practice which motivated the behavior change.

    as_set = {JustEq(1), JustEq(2)}
    print(JustEq(1) in as_set)  # prints False
    print(JustEq(1) in list(as_set))  # prints True

    In order to fix this error and avoid behavior differences between Python 2 and Python 3, classes should either explicitly set __hash__ to None or implement a hashing function.

    class JustEq(object):
       def __init__(self, x):
         self.x = x
       def __eq__(self, other):
         return self.x == other.x
       __hash__ = None
    {JustEq(1), JustEq(2)}  # Now throws an exception in both Python 2 and Python 3.

•   3 new Python 3 checkers were added, div-method, idiv-method and rdiv-method. The magic methods __div__ and __idiv__ have been phased out in Python 3 in favor of __truediv__. Classes implementing __div__ that still need to be used from Python 2 code not using from __future__ import division should implement __truediv__ and alias __div__ to that implementation.

    from __future__ import division
    class DivisibleThing(object):
       def __init__(self, x):
         self.x = x
       def __truediv__(self, other):
         return DivisibleThing(self.x / other.x)
       __div__ = __truediv__

•   A new Python 3 checker was added to warn about accessing the message attribute on Exceptions. The message attribute was deprecated in Python 2.7 and was removed in Python 3. See https://peps.python.org/pep-0352/#retracted-ideas for more information.

    try:
      raise Exception("Oh No!!")
    except Exception as e:
      print(e.message)

    Instead of relying on the message attribute, you should explicitly cast the exception to a string:

    try:
      raise Exception("Oh No!!")
    except Exception as e:
      print(str(e))

•   A new Python 3 checker was added to warn about using encode or decode on strings with non-text codecs. This check also checks calls to open with the keyword argument encoding. See https://docs.python.org/3/whatsnew/3.4.html#improvements-to-codec-handling for more information.

    'hello world'.encode('hex')

    Instead of using the encode method for non-text codecs use the codecs module.

    import codecs
    codecs.encode('hello world', 'hex')

•   A new warning was added, overlapping-except, which is emitted when an except handler treats two exceptions which are overlapping. This means that one exception is an ancestor of the other one or it is just an alias.

    For example, in Python 3.3+, IOError is an alias for OSError. In addition, socket.error is an alias for OSError. The intention is to find cases like the following:

    import socket
    try:
        pass
    except (ConnectionError, IOError, OSError, socket.error):
        pass

•   A new Python 3 checker was added to warn about accessing sys.maxint. This attribute was removed in Python 3 in favor of sys.maxsize.

    import sys
    print(sys.maxint)

    Instead of using sys.maxint, use sys.maxsize

    import sys
    print(sys.maxsize)

•   A new Python 3 checker was added to warn about importing modules that have either moved or been removed from the standard library.

    One of the major undertakings with Python 3 was a reorganization of the standard library to remove old or supplanted modules and reorganize some of the existing modules. As a result, roughly 100 modules that exist in Python 2 no longer exist in Python 3. See https://peps.python.org/pep-3108/ and https://peps.python.org/pep-0004/ for more information. There were suggestions on how to handle this, at pythonhosted.org/six/#module-six.moves (dead link) or python3porting.com/stdlib.html (dead link).

    from cStringIO import StringIO

    Instead of directly importing the deprecated module, either use six.moves or a conditional import.

    from six.moves import cStringIO as StringIO
    if sys.version_info[0] >= 3:
        from io import StringIO
    else:
        from cStringIO import StringIO

    This checker will assume any imports that happen within a conditional or a try/except block are valid.

•   A new Python 3 checker was added to warn about accessing deprecated functions on the string module. Python 3 removed functions that were duplicated from the builtin str class. See https://docs.python.org/2/library/string.html#deprecated-string-functions for more information.

    import string
    print(string.upper('hello world!'))

    Instead of using string.upper, call the upper method directly on the string object.

    "hello world!".upper()

•   A new Python 3 checker was added to warn about calling str.translate with the removed deletechars parameter. str.translate is frequently used as a way to remove characters from a string.

    'hello world'.translate(None, 'low')

    Unfortunately, there is not an idiomatic way of writing this call in a 2and3 compatible way. If this code is not in the critical path for your application and the use of translate was a premature optimization, consider using re.sub instead:

    import re
    chars_to_remove = re.compile('[low]')
    chars_to_remove.sub('', 'hello world')

    If this code is in your critical path and must be as fast as possible, consider declaring a helper method that varies based upon Python version.

    if six.PY3:
        def _remove_characters(text, deletechars):
            return text.translate({ord(x): None for x in deletechars})
    else:
        def _remove_characters(text, deletechars):
            return text.translate(None, deletechars)

•   A new refactoring check was added, consider-using-ternary, which is emitted when pylint encounters constructs which were used to emulate ternary statement before it was introduced in Python 2.5.

    value = condition and truth_value or false_value

    Warning can be fixed by using standard ternary construct:

    value = truth_value if condition else false_value

•   A new refactoring check was added, trailing-comma-tuple, which is emitted when pylint finds an one-element tuple, created by a stray comma. This can suggest a potential problem in the code and it is recommended to use parentheses in order to emphasise the creation of a tuple, rather than relying on the comma itself.

    The warning is emitted for such a construct:

    a = 1,

    The warning can be fixed by adding parentheses:

    a = (1, )

•   Two new check were added for detecting an unsupported operation over an instance, unsupported-assignment-operation and unsupported-delete-operation. The first one is emitted whenever an object does not support item assignment, while the second is emitted when an object does not support item deletion:

    class A:
        pass
    instance = A()
    instance[4] = 4 # unsupported-assignment-operation
    del instance[4] # unsupported-delete-operation

•   A new check was added, relative-beyond-top-level, which is emitted when a relative import tries to access too many levels in the current package.

•   A new check was added, trailing-newlines, which is emitted when a file has trailing new lines.

•   invalid-length-returned check was added, which is emitted when a __len__ implementation does not return a non-negative integer.

•   There is a new extension, pylint.extensions.mccabe, which can be used for computing the McCabe complexity of classes and functions.

    You can enable this extension through --load-plugins=pylint.extensions.mccabe

•   A new check was added, used-prior-global-declaration. This is emitted when a name is used prior a global declaration, resulting in a SyntaxError in Python 3.6.

•   A new message was added, assign-to-new-keyword. This is emitted when used name is known to become a keyword in future Python release. Assignments to keywords would result in SyntaxError after switching to newer interpreter version.

    # While it's correct in Python 2.x, it raises a SyntaxError in Python 3.x
    True = 1
    False = 0
    # Same as above, but it'll be a SyntaxError starting from Python 3.7
    async = "async"
    await = "await"

  Other Changes

•   We don't emit by default no-member if we have opaque inference objects in the inference results

    This is controlled through the new flag --ignore-on-opaque-inference, which is by default True. The inference can return multiple potential results while evaluating a Python object, but some branches might not be evaluated, which results in partial inference. In that case, it might be useful to still emit no-member and other checks for the rest of the inferred objects.

•   Namespace packages are now supported by pylint. This includes both explicit namespace packages and implicit namespace packages, supported in Python 3 through PEP 420.

•   A new option was added, --analyse-fallback-block.

    This can be used to support both Python 2 and 3 compatible import block code, which means that the import block might have code that exists only in one or another interpreter, leading to false positives when analysed. By default, this is false, you can enable the analysis for both branches using this flag.

•   ignored-argument-names option is now used for ignoring arguments for unused-variable check.

    This option was used for ignoring arguments when computing the correct number of arguments a function should have, but for handling the arguments with regard to unused-variable check, dummy-variables-rgx was used instead. Now, ignored-argument-names is used for its original purpose and also for ignoring the matched arguments for the unused-variable check. This offers a better control of what should be ignored and how. Also, the same option was moved from the design checker to the variables checker, which means that the option now appears under the [VARIABLES] section inside the configuration file.

•   A new option was added, redefining-builtins-modules, for controlling the modules which can redefine builtins, such as six.moves and future.builtins.

•   A new option was added, ignore-patterns, which is used for building a ignore list of directories and files matching the regex patterns, similar to the ignore option.

•   The reports are now disabled by default, as well as the information category warnings.

•   arguments-differ check was rewritten to take in consideration keyword only parameters and variadics.

    Now it also complains about losing or adding capabilities to a method, by introducing positional or keyword variadics. For instance, pylint now complains about these cases:

    class Parent(object):
        def foo(self, first, second):
            ...
        def bar(self, **kwargs):
            ...
        def baz(self, *, first):
            ...
    class Child(Parent):
        # Why subclassing in the first place?
        def foo(self, *args, **kwargs):
            # mutate args or kwargs.
            super(Child, self).foo(*args, **kwargs)
        def bar(self, first=None, second=None, **kwargs):
            ...
            # The overridden method adds two new parameters,
            # which can also be passed as positional arguments,
            # breaking the contract of the parent's method.
        def baz(self, first):
            ...
            # Not keyword-only

•   redefined-outer-name is now also emitted when a nested loop's target variable is the same as an outer loop.

    for i, j in [(1, 2), (3, 4)]:
        for j in range(i):
            print(j)

•   relax character limit for method and function names that starts with _. This will let people to use longer descriptive names for methods and functions with a shorter scope (considered as private). The same idea applies to variable names, only with an inverse rule: you want long descriptive names for variables with bigger scope, like globals.

•   Add InvalidMessageError exception class and replace assert in pylint.utils with raise InvalidMessageError.

•   UnknownMessageError (formerly UnknownMessage) and EmptyReportError (formerly EmptyReport) are now provided by the new pylint.exceptions submodule instead of pylint.utils as before.

•   We now support inline comments for comma separated values in the configurations

    For instance, you can now use the # sign for having comments inside comma separated values, as seen below:

    disable=no-member, # Don't care about it for now
            bad-indentation, # No need for this
            import-error

    Of course, interweaving comments with values is also working:

    disable=no-member,
            # Don't care about it for now
            bad-indentation # No need for this

    This works by setting the inline comment prefixes accordingly.

•   Added epytext docstring support to the docparams extension.

•   We added support for providing hints when not finding a missing member.

    For example, given the following code, it should be obvious that the programmer intended to use the mail attribute, rather than email.

    class Contribution:
        def __init__(self, name, email, date):
            self.name = name
            self.mail = mail
            self.date = date
    for c in contributions:
        print(c.email) # Oups

    pylint will now warn that there is a chance of having a typo, suggesting new names that could be used instead.

    $ pylint a.py
    E: 8,10: Instance of 'Contribution' has no 'email' member; maybe 'mail'?

    The behaviour is controlled through the --missing-member-hint option. Other options that come with this change are --missing-member-max-choices for choosing the total number of choices that should be picked in this situation and --missing-member-hint-distance, which specifies a metric for computing the distance between the names (this is based on Levenshtein distance, which means the lower the number, the more pickier the algorithm will be).

•   PyLinter.should_analyze_file has a new parameter, is_argument, which specifies if the given path is a pylint argument or not.

    should_analyze_file is called whenever pylint tries to determine if a file should be analyzed, defaulting to files with the .py extension, but this function gets called only in the case where the said file is not passed as a command line argument to pylint. This usually means that pylint will analyze a file, even if that file has a different extension, as long as the file was explicitly passed at command line. Since should_analyze_file cannot be overridden to handle all the cases, the check for the provenience of files was moved into should_analyze_file. This means we now can write something similar with this example, for ignoring every file respecting the desired property, disregarding the provenience of the file, being it a file passed as CLI argument or part of a package.

    from pylint.lint import Run, PyLinter
    class CustomPyLinter(PyLinter):
         def should_analyze_file(self, modname, path, is_argument=False):
             if respect_condition(path):
                 return False
             return super().should_analyze_file(modname, path, is_argument=is_argument)
    class CustomRun(Run):
         LinterClass = CustomPyLinter
    CustomRun(sys.argv[1:])

•   Imports aliased with underscore are skipped when checking for unused imports.

•   bad-builtin and redefined-variable-type are now extensions, being disabled by default. They can be enabled through: --load-plugins=pylint.extensions.redefined_variable_type,pylint.extensions.bad_builtin

•   Imports checker supports new switch allow-wildcard-with-all which disables warning on wildcard import when imported module defines __all__ variable.

•   differing-param-doc is now used for the differing part of the old missing-param-doc, and differing-type-doc for the differing part of the old missing-type-doc.

  Bug fixes

•   Fix a false positive of redundant-returns-doc, occurred when the documented function was using yield instead of return.

•   Fix a false positive of missing-param-doc and missing-type-doc, occurred when a class docstring uses the For the parameters, see magic string but the class __init__ docstring does not, or vice versa.

•   Added proper exception type inference for missing-raises-doc. Now:

    def my_func():
        """"My function."""
        ex = ValueError('foo')
        raise ex

    will properly be flagged for missing documentation of :raises ValueError: instead of :raises ex:, among other scenarios.

•   Fix false positives of missing-[raises|params|type]-doc due to not recognizing valid keyword synonyms supported by Sphinx.

•   More thorough validation in MessagesStore.register_messages() to detect conflicts between a new message and any existing message id, symbol, or old_names.

•   We now support having plugins that shares the same name and with each one providing options.

    A plugin can be logically split into multiple classes, each class providing certain capabilities, all of them being tied under the same name. But when two or more such classes are also adding options, then pylint crashed, since it already added the first encountered section. Now, these should work as expected.

    from pylint.checkers import BaseChecker
    class DummyPlugin1(BaseChecker):
        name = 'dummy_plugin'
        msgs = {'I9061': ('Dummy short desc 01', 'dummy-message-01', 'Dummy long desc')}
        options = (
            ('dummy_option_1', {
                'type': 'string',
                'metavar': '<string>',
                'help': 'Dummy option 1',
            }),
        )
    class DummyPlugin2(BaseChecker):
        name = 'dummy_plugin'
        msgs = {'I9060': ('Dummy short desc 02', 'dummy-message-02', 'Dummy long desc')}
        options = (
            ('dummy_option_2', {
                'type': 'string',
                'metavar': '<string>',
                'help': 'Dummy option 2',
            }),
        )
    def register(linter):
        linter.register_checker(DummyPlugin1(linter))
        linter.register_checker(DummyPlugin2(linter))

•   We do not yield unused-argument for singledispatch implementations and do not warn about function-redefined for multiple implementations with same name.

    from functools import singledispatch
    @singledispatch
    def f(x):
        return 2*x
    @f.register(str)
    def _(x):
        return -1
    @f.register(int)
    @f.register(float)
    def _(x):
        return -x

•   unused-variable checker has new functionality of warning about unused variables in global module namespace. Since globals in module namespace may be a part of exposed API, this check is disabled by default. For enabling it, set allow-global-unused-variables option to false.

•   Fix a false-positive logging-format-interpolation message, when format specifications are used in formatted string. In general, these operations are not always convertible to old-style formatting used by logging module.

•   Added a new switch single-line-class-stmt to allow single-line declaration of empty class bodies (as seen in the example below). Pylint won't emit a multiple-statements message when this option is enabled.

    class MyError(Exception): pass

•   too-many-format-args and too-few-format-args are emitted correctly (or not emitted at all, when exact count of elements in RHS cannot be inferred) when starred expressions are used in RHS tuple. For example, code block as shown below detects correctly that the used tuple has in fact three elements, not two.

    meat = ['spam', 'ham']
    print('%s%s%s' % ('eggs', *meat))

•   cyclic-import checker supports local disable clauses. When one of cycle imports was done in scope where disable clause was active, cycle is not reported as violation.

  Removed Changes

•   pylint-gui was removed, because it was deemed unfit for being included in pylint. It had a couple of bugs and misfeatures, its usability was subpar and since its development was neglected, we decided it is best to move on without it.

•   The HTML reporter was removed, including the --output-format=html option. It was lately a second class citizen in Pylint, being mostly neglected. Since we now have the JSON reporter, it can be used as a basis for building more prettier HTML reports than what Pylint can currently generate. This is part of the effort of removing cruft from Pylint, by removing less used features.

•   The --files-output option was removed. While the same functionality cannot be easily replicated, the JSON reporter, for instance, can be used as a basis for generating the messages per each file.

•   --required-attributes option was removed.

•   --ignore-iface-methods option was removed.

•   The --optimize-ast flag was removed.

    The option was initially added for handling pathological cases, such as joining too many strings using the addition operator, which was leading pylint to have a recursion error when trying to figure out what the string was. Unfortunately, we decided to ignore the issue, since the pathological case would have happen when the code was parsed by Python as well, without actually reaching the runtime step and as such, we decided to remove the error altogether.

•   epylint.py_run's script parameter was removed.

    Now epylint.py_run is always using the underlying epylint.lint method from the current interpreter. This avoids some issues when multiple instances of pylint are installed, which means that epylint.py_run might have ran a different epylint script than what was intended.

  Full changelog

  What's New in Pylint 1.7.1?

Release date: 2017-04-17

•   Fix a false positive which occurred when an exception was reraised

    Closes #1419

•   Fix a false positive of disallow-trailing-tuple

    The check was improved by verifying for non-terminating newlines, which should exempt function calls and function definitions from the check

    Closes #1424

  What's New in Pylint 1.7?

Release date: 2017-04-13

•   Don't emit missing-final-newline or trailing-whitespace for formfeeds (page breaks).

    Closes #1218 and #1219

•   Don't emit by default no-member if we have opaque inference objects in the inference results

    This is controlled through the new flag ignore-on-opaque-inference, which is by default True. The inference can return multiple potential results while evaluating a Python object, but some branches might not be evaluated, which results in partial inference. In that case, it might be useful to still emit no-member and other checks for the rest of the inferred objects.

•   Added new message assign-to-new-keyword to warn about assigning to names which will become a keyword in future Python releases.

    Closes #1351

•   Split the 'missing or differing' in parameter documentation in different error. 'differing-param-doc' covers the differing part of the old 'missing-param-doc', and 'differing-type-doc' covers the differing part of the old 'missing-type-doc'

    Closes #1342

•   Added a new error, 'used-prior-global-declaration', which is emitted when a name is used prior a global declaration in a function. This causes a SyntaxError in Python 3.6

    Closes #1257

•   The protocol checks are emitting their messages when a special method is set to None.

    Closes #1263

•   Properly detect if imported name is assigned to same name in different scope.

    Closes #636, #848, #851, and #900

•   Require one space for annotations with type hints, as per PEP 8.

•   'trailing-comma-tuple' check was added

    This message is emitted when pylint finds an one-element tuple, created by a stray comma. This can suggest a potential problem in the code and it is recommended to use parentheses in order to emphasise the creation of a tuple, rather than relying on the comma itself.

•   Don't emit not-callable for instances with unknown bases.

    Closes #1213

•   Treat keyword only arguments the same as positional arguments with regard to unused-argument check

•   Don't try to access variables defined in a separate scope when checking for protected-access

•   Added new check to detect incorrect usage of len(SEQUENCE) inside test conditions.

•   Added new extension to detect comparisons against empty string constants

•   Added new extension to detect comparisons of integers against zero

•   Added new error conditions for 'bad-super-call'

    Now detects super(type(self), self) and super(self.__class__, self) which can lead to recursion loop in derived classes.

•   PyLinter.should_analyze_file has a new optional parameter, called is_argument

    Closes #1079

•   Add attribute hints for missing members

    Closes #1035

•   Add a new warning, 'redefined-argument-from-local'

    Closes #649

•   Support inline comments for comma separated values in the config file

    Closes #1024

•   epylint.py_run's script parameter was removed.

•   epylint.py_run now uses shell=False for running the underlying process.

    Closes #441

•   Added a new warning, 'useless-super-delegation'

    Close 839.

•   Added a new error, 'invalid-metaclass', raised when we can detect that a class is using an improper metaclass.

    Closes #579

•   Added a new refactoring message, 'literal-comparison'.

    Closes #786

•   arguments-differ takes in consideration kwonlyargs and variadics

    Closes #983

•   Removed --optimized-ast

    Fixes part of #975

•   Removed --files-output option

    Fixes part of #975

•   Removed pylint-gui from the package.

•   Removed the HTML reporter

    Fixes part of #975

•   ignored-argument-names is now used for ignoring arguments for unused-variable check.

    This option was used for ignoring arguments when computing the correct number of arguments a function should have, but for handling the arguments with regard to unused-variable check, dummy-variables-rgx was used instead. Now, ignored-argument-names is used for its original purpose and also for ignoring the matched arguments for the unused-variable check. This offers a better control of what should be ignored and how. Also, the same option was moved from the design checker to the variables checker, which means that the option now appears under the [VARIABLES] section inside the configuration file.

    Closes #862.

•   Fix a false positive for keyword variadics with regard to keyword only arguments.

    If a keyword only argument was necessary for a function, but that function was called with keyword variadics (**kwargs), then we were emitting a missing-kwoa false positive, which is now fixed.

    Closes #934.

•   Fix some false positives with unknown sized variadics.

    Closes #878

•   Added a new extension, check_docstring, for checking PEP 257 conventions.

    Closes #868.

•   config files with BOM markers can now be read.

    Closes #864.

•   epylint.py_run does not crash on big files, using .communicate() instead of .wait()

    Closes #599

•   Disable reports by default and show the evaluation score by default

    The reports were disabled by default in order to simplify the interaction between the tool and the users. The score is still shown by default, as a way of closely measuring when it increases or decreases due to changes brought to the code.

    Refs #746

•   Disable the information category messages by default. This is a step towards making pylint more sane.

    Refs #746.

•   Catch more cases as not proper iterables for __slots__ with regard to invalid-slots pattern.

    Closes #775

•   empty indent strings are rejected.

•   Added a new error, 'relative-beyond-top-level', which is emitted when a relative import was attempted beyond the top level package.

    Closes #588

•   Added a new warning, 'unsupported-assignment-operation', which is emitted when item assignment is tried on an object which doesn't have this ability.

    Closes #591

•   Added a new warning, 'unsupported-delete-operation', which is emitted when item deletion is tried on an object which doesn't have this ability.

    Closes #592

•   Fix a false positive of 'redundant-returns-doc', occurred when the documented function was using yield instead of return.

    Closes #984.

•   Fix false positives of 'missing-[raises|params|type]-doc' due to not recognizing keyword synonyms supported by Sphinx.

•   Added a new refactoring message, 'consider-merging-isinstance', which is emitted whenever we can detect that consecutive isinstance calls can be merged together.

    Closes #968

•   Fix a false positive of 'missing-param-doc' and 'missing-type-doc', occurred when a class docstring uses the 'For the parameters, see' magic string but the class __init__ docstring does not, or vice versa.

•   redefined-outer-name is now also emitted when a nested loop's target variable is the same as a target variable in an outer loop.

    Closes #911.

•   Added proper exception type inference for 'missing-raises-doc'.

•   Added InvalidMessageError exception class to replace asserts in pylint.utils.

•   More thorough validation in MessagesStore.register_messages() to avoid one message accidentally overwriting another.

•   InvalidMessageError, UnknownMessage, and EmptyReport exceptions are moved to the new pylint.exceptions submodule.

•   UnknownMessage and EmptyReport are renamed to UnknownMessageError and EmptyReportError.

•   Warnings 'missing-returns-type-doc' and 'missing-yields-type-doc' have each been split into two warnings - 'missing-[return|yield]-doc' and 'missing-[return|yield]-type-doc'.

•   Added epytext support to docparams extension.

    Closes #1029

•   Support having plugins with the same name and with options defined

    Closes #1018

•   Sort configuration options in a section

    Closes #1087

•   Added a new Python 3 warning around implementing '__div__', '__idiv__', or '__rdiv__' as those methods are phased out in Python 3.

•   Added a new warning, 'overlapping-except', which is emitted when two exceptions in the same except-clause are aliases for each other or one exceptions is an ancestor of another.

•   Avoid crashing on ill-formatted strings when checking for string formatting errors.

•   Added a new Python 3 warning for calling 'str.encode' or 'str.decode' with a non-text encoding.

•   Added new coding convention message, 'single-string-used-for-slots'.

    Closes #1166

•   Added a new Python 3 check for accessing 'sys.maxint' which was removed in Python 3 in favor of 'sys.maxsize'

•   Added a new Python 3 check for bad imports.

•   Added a new Python 3 check for accessing deprecated string functions.

•   Do not warn about unused arguments or function being redefined in singledispatch registered implementations.

    Closes #1032 and #1034

•   Added refactoring message 'no-else-return'.

•   Improve unused-variable checker to warn about unused variables in module scope.

    Closes #919

•   Ignore modules import as _ when checking for unused imports.

    Closes #1190

•   Improve handing of Python 3 classes with metaclasses declared in nested scopes.

    Closes #1177

•   Added refactoring message 'consider-using-ternary'.

    Closes #1204

•   Bug-fix for false-positive logging-format-interpolation` when format specifications are used in formatted string.

    Closes #572

•   Added a new switch single-line-class-stmt to allow single-line declaration of empty class bodies.

    Closes #738

•   Protected access in form type(self)._attribute are now allowed.

    Closes #1031

•   Let the user modify msg-template when Pylint is called from a Python script

    Closes #1269

•   Imports checker supports new switch allow-wildcard-with-all which disables warning on wildcard import when imported module defines __all__ variable.

    Closes #831

•   too-many-format-args and too-few-format-args are emitted correctly when starred expression are used in RHS tuple.

    Closes #957

•   cyclic-import checker supports local disable clauses. When one of cycle imports was done in scope where disable clause was active, cycle is not reported as violation.

    Closes #59

  What's New In Pylint 1.6

From pylint's beginning to pylint 2.14.0 included, we had a changelog that contained all nontrivial changes to Pylint, including changes that were not user facing, i.e. change that might interest you only if you're a developer working on pylint or pylint plugins or an open-source historian.

From pylint 1.6.0 to 2.14.0, on top of the full changelog there was also a summary of (mostly user facing) changes.

Ticket numbers can be internal to logilab or come from bitbucket.

  Summary -- Release highlights

Nothing major.

  New checkers

•   We added a new recommendation check, consider-iterating-dictionary, which is emitted when a dictionary is iterated by using .keys().

    For instance, the following code would trigger this warning, since the dictionary's keys can be iterated without calling the method explicitly.

    for key in dictionary.keys():
        ...
    # Can be refactored to:
    for key in dictionary:
        ...

•   trailing-newlines check was added, which is emitted when a file has trailing newlines.

•   invalid-length-returned check was added, which is emitted when the __len__ special method returns something else than a non-negative number. For instance, this example is triggering it:

    class Container(object):
        def __len__(self):
            return self._items # Oups, forgot to call len() over it.

•   Add a new check to the check_docs extension for looking for duplicate constructor parameters in a class constructor docstring or in a class docstring.

    The check multiple-constructor-doc is emitted when the parameter is documented in both places.

•   We added a new extension plugin, pylint.extensions.mccabe, which can be used for warning about the complexity in the code.

    You can enable it as in:

    $ pylint module_or_project --load-plugins=pylint.extensions.mccabe

    See more at Design checker

  New features

•   generated-members now supports qualified names through regular expressions.

    For instance, for ignoring all the errors generated by numpy.core's attributes, we can now use:

    $ pylint a.py --generated-members=numpy.*

•   Add the ability to ignore files based on regex matching, with the new --ignore-patterns option.

    Rather than clobber the existing ignore option, we decided to have a separate option for it. For instance, for ignoring all the test files, we can now use:

    $ pylint myproject --ignore-patterns=test.*?py

•   We added a new option, redefining-builtins-modules, which is used for defining the modules which can redefine builtins. pylint will emit an error when a builtin is redefined, such as defining a variable called next. But in some cases, the builtins can be redefined in the case they are imported from other places, different than the builtins module, such is the case for six.moves, which contains more forward-looking functions:

    $ cat a.py
    # Oups, now pylint emits a redefined-builtin message.
    from six.moves import open
    $ pylint a.py --redefining-builtins-modules=six.moves

    Default values: six.moves,future.builtins

  Bug fixes

•   Fixed a bug where the top name of a qualified import was detected as an unused variable.

•   We don't warn about invalid-sequence-index if the indexed object has unknown base classes, that Pylint cannot deduce.

  Other Changes

•   The bad-builtin check was moved into an extension.

    The check was complaining about used builtin functions which were supposed to not be used. For instance, map and filter were falling into this category, since better alternatives can be used, such as list comprehensions. But the check was annoying, since using map or filter can have its use cases and as such, we decided to move it to an extension check instead. It can now be enabled through --load-plugins=pylint.extensions.bad_builtin.

•   We use the configparser backport internally, for Python 2.

    This allows having comments inside list values, in the configuration, such as:

    disable=no-member,
            # Don't like this check
            bad-indentation

•   We now use the isort package internally.

    This improves the `wrong-import-order check, so now we should have less false positives regarding the import order.

•   We do not emit import-error or no-name-in-module for fallback import blocks by default.

    A fallback import block can be considered a TryExcept block, which contains imports in both branches, such as:

    try:
        import urllib.request as request
    except ImportError:
        import urllib2 as request

    In the case where pylint can not find one import from the except branch, then it will emit an import-error, but this gets cumbersome when trying to write compatible code for both Python versions. As such, we don't check these blocks by default, but the analysis can be enforced by using the new --analyse-fallback-block flag.

•   reimported is emitted when the same name is imported from different module, as in:

    from collections import deque, OrderedDict, deque

  Deprecated features

•   The HTML support was deprecated and will be eventually removed in Pylint 1.7.0.

    This feature was lately a second class citizen in Pylint, being often neglected and having a couple of bugs. Since we now have the JSON reporter, this can be used as a basis for more prettier HTML outputs than what Pylint can currently offer.

•   The --files-output option was deprecated and will be eventually removed in Pylint 1.7.0.

•   The --optimize-ast option was deprecated and will be eventually removed in Pylint 1.7.0.

    The option was initially added for handling pathological cases, such as joining too many strings using the addition operator, which was leading pylint to have a recursion error when trying to figure out what the string was. Unfortunately, we decided to ignore the issue, since the pathological case would have happen when the code was parsed by Python as well, without actually reaching the runtime step and as such, we will remove the option in the future.

•   The check_docs extension is now deprecated. The extension is still available under the docparams name, so this should work:

    $ pylint module_or_package --load-extensions=pylint.extensions.docparams

    The old name is still kept for backward compatibility, but it will be eventually removed.

  Removed features

•   None yet

  Full changelog

  What's new in Pylint 1.6.3?

Release date: 2016-07-18

•   Do not crash when inferring uninferable exception types for docparams extension

    Closes #998

  What's new in Pylint 1.6.2?

Release date: 2016-07-15

•   Do not crash when printing the help of options with default regular expressions

    Closes #990

•   More granular versions for deprecated modules.

    Closes #991

  What's new in Pylint 1.6.1?

Release date: 2016-07-07

•   Use environment markers for supporting conditional dependencies.

  What's New in Pylint 1.6.0?

Release date: 2016-07-03

•   Added a new extension, pylint.extensions.mccabe, for warning about complexity in code.

•   Deprecate support for --optimize-ast

    Fixes part of #975

•   Deprecate support for the HTML output

    Fixes part of #975

•   Deprecate support for --output-files

    Fixes part of #975

•   Fixed a documentation error for the check_docs extension.

    Closes #735

•   Made the list of property-defining decorators configurable.

•   Fix a bug where the top name of a qualified import was detected as unused variable.

    Closes #923

•   bad-builtin is now an extension check.

•   generated-members support qualified name through regular expressions.

    For instance, one can specify a regular expression as --generated-members=astroid.node_classes.* for ignoring every no-member error that is accessed as in astroid.node_classes.missing.object.

•   Add the ability to ignore files based on regex matching, with the new --ignore-patterns option. Allow for multiple ignore patterns to be specified. Rather than clobber the existing ignore option, we introduced a new one called ignore-patterns.

    Closes #156

•   Added a new error, 'trailing-newlines', which is emitted when a file has trailing new lines.

    Closes #682

•   Add a new option, 'redefining-builtins-modules', for controlling the modules which can redefine builtins, such as six.moves and future.builtins.

    Closes #464

•   'reimported' is emitted when the same name is imported from different module.

    Closes #162

•   Add a new recommendation checker, 'consider-iterating-dictionary', which is emitted which is emitted when a dictionary is iterated through .keys().

    Closes #699

•   Use the configparser backport for Python 2

    This fixes a problem we were having with comments inside values, which is fixed in Python 3's configparser.

    Closes #828

•   A new error was added, 'invalid-length-returned', when the __len__ special method returned something else than a non-negative number.

    Closes #557

•   Switch to using isort internally for wrong-import-order.

    Closes #879

•   check_docs extension can find constructor parameters in __init__.

    Closes #887

•   Don't warn about invalid-sequence-index if the indexed object has unknown base classes.

    Closes #867

•   Don't crash when checking, for super-init-not-called, a method defined in an if block.

•   Do not emit import-error or no-name-in-module for fallback import blocks by default.

    Until now, we warned with these errors when a fallback import block (a TryExcept block that contained imports for Python 2 and 3) was found, but this gets cumbersome when trying to write compatible code. As such, we don't check these blocks by default, but the analysis can be enforced by using the new --analyse-fallback-block flag.

    Closes #769.

    Ticket numbers are almost can be internal to Logilab, or from bitbucket. In latest version it's also github issues.

  What's New In Pylint 1.5

  What's New in Pylint 1.5.5?

Release date: 2016-03-21

•   Let visit_importfrom from Python 3 porting checker be called when everything is disabled

    Because the visit method was filtering the patterns it was expecting to be activated, it didn't run when everything but one pattern was disabled, leading to spurious false positives

    Closes #852

•   Don't emit unsubscriptable-value for classes with unknown base classes.

    Closes #776.

•   Use an OrderedDict for storing the configuration elements

    This fixes an issue related to impredictible order of the disable / enable elements from a config file. In certain cases, the disable was coming before the enable which resulted in classes of errors to be enabled, even though the intention was to disable them. The best example for this was in the context of running multiple processes, each one of it having different enables / disables that affected the output.

    Closes #815

•   Don't consider bare and broad except handlers as ignoring NameError, AttributeError and similar exceptions, in the context of checkers for these issues.

    Closes #826

  What's New in Pylint 1.5.4?

Release date: 2016-01-15

•   Merge StringMethodChecker with StringFormatChecker. This fixes a bug where disabling all the messages and enabling only a handful of messages from the StringFormatChecker would have resulted in no messages at all.

•   Don't apply unneeded-not over sets.

  What's New in Pylint 1.5.3?

Release date: 2016-01-11

•   Handle the import fallback idiom with regard to wrong-import-order.

    Closes #750

•   Decouple the displaying of reports from the displaying of messages

    Some reporters are aggregating the messages instead of displaying them when they are available. The actual displaying was conflatted in the generate_reports. Unfortunately this behaviour was flaky and in the case of the JSON reporter, the messages weren't shown at all if a file had syntax errors or if it was missing. In order to fix this, the aggregated messages can now be displayed with Reporter.display_message, while the reports are displayed with display_reports.

    Closes #766 Closes #765

•   Ignore function calls with variadic arguments without a context.

    Inferring variadic positional arguments and keyword arguments will result into empty Tuples and Dicts, which can lead in some cases to false positives with regard to no-value-for-parameter. In order to avoid this, until we'll have support for call context propagation, we're ignoring such cases if detected.

    Closes #722

•   Treat AsyncFunctionDef just like FunctionDef nodes, by implementing visit_asyncfunctiondef in terms of visit_functiondef.

    Closes #767

•   Take in account kwonlyargs when verifying that arguments are defined with the check_docs extension.

    Closes #745

•   Suppress reporting 'unneeded-not' inside __ne__ methods

    Closes #749

  What's New in Pylint 1.5.2?

Release date: 2015-12-21

•   Don't crash if graphviz is not installed, instead emit a warning letting the user to know.

    Closes #168

•   Accept only functions and methods for the deprecated-method checker.

    This prevents a crash which can occur when an object doesn't have .qname() method after the inference.

•   Don't emit super-on-old-class on classes with unknown bases.

    Closes #721

•   Allow statements in if or try blocks containing imports.

    Closes #714

  What's New in Pylint 1.5.1?

Release date: 2015-12-02

•   Fix a crash which occurred when old visit methods are encountered in plugin modules.

    Closes #711

•   Add wrong-import-position to check_messages's decorator arguments for ImportChecker.leave_module This fixes an esoteric bug which occurs when ungrouped-imports and wrong-import-order are disabled and pylint is executed on multiple files. What happens is that without wrong-import-position in check_messages, leave_module will never be called, which means that the first non-import node from other files might leak into the current file, leading to wrong-import-position being emitted by pylint.

•   Fix a crash which occurred when old visit methods are encountered in plugin modules.

    Closes #711

•   Don't emit import-self and cyclic-import for relative imports of modules with the same name as the package itself.

    Closes #708 Closes #706.

  What's New in Pylint 1.5.0?

Release date: 2015-11-29

•   Added multiple warnings related to imports. 'wrong-import-order' is emitted when PEP 8 recommendations regarding imports are not respected (that is, standard imports should be followed by third-party imports and then by local imports). 'ungrouped-imports' is emitted when imports from the same package or module are not placed together, but scattered around in the code. 'wrong-import-position' is emitted when code is mixed with imports, being recommended for the latter to be at the top of the file, in order to figure out easier by a human reader what dependencies a module has.

    Closes #692

•   Added a new refactoring warning, 'unneeded-not', emitted when an expression with the not operator could be simplified.

    Closes #670

•   Added a new refactoring warning, 'simplifiable-if-statement', used when an if statement could be reduced to a boolean evaluation of its test.

    Closes #698

•   Added a new refactoring warning, 'too-many-boolean-expressions', used when an if statement contains too many boolean expressions, which makes the code less maintainable and harder to understand.

    Closes #677

•   Property methods are shown as attributes instead of functions in pyreverse class diagrams.

    Closes #284

•   Add a new refactoring error, 'too-many-nested-blocks', which is emitted when a function or a method has too many nested blocks, which makes the code less readable and harder to understand.

    Closes #668

•   Add a new error, 'unsubscriptable-object', that is emitted when value used in subscription expression doesn't support subscription (i.e. doesn't define __getitem__ method).

•   Don't warn about abstract classes instantiated in their own body.

    Closes #627

•   Obsolete options are not present by default in the generated configuration file.

    Closes #632

•   non-iterator-returned can detect classes with iterator-metaclasses.

    Closes #679

•   Add a new error, 'unsupported-membership-test', emitted when value to the right of the 'in' operator doesn't support membership test protocol (i.e. doesn't define __contains__/__iter__/__getitem__)

•   Add new errors, 'not-an-iterable', emitted when non-iterable value is used in an iterating context (starargs, for-statement, comprehensions, etc), and 'not-a-mapping', emitted when non-mapping value is used in a mapping context.

    Closes #563

•   Make 'no-self-use' checker not emit a warning if there is a 'super()' call inside the method.

    Closes #667

•   Add checker to identify multiple imports on one line.

    Closes #598

•   Fix unused-argument false positive when the "+=" operator is used.

    Closes #518

•   Don't emit import-error for ignored modules. PyLint will not emit import errors for any import which is, or is a subpackage of, a module in the ignored-modules list.

    Closes #223

•   Fix unused-import false positive when the import is used in a class assignment.

    Closes #475

•   Add a new error, 'not-context-manager', emitted when something that doesn't implement __enter__ and __exit__ is used in a with statement.

•   Add a new warning, 'confusing-with-statement', emitted by the base checker, when an ambiguous looking with statement is used. For example with open() as first, second which looks like a tuple assignment but is actually 2 context managers.

•   Add a new warning, 'duplicate-except', emitted when there is an exception handler which handles an exception type that was handled before.

    Closes #485

•   A couple of warnings got promoted to errors, since they could uncover potential bugs in the code. These warnings are: assignment-from-none, unbalanced-tuple-unpacking, unpacking-non-sequence, non-iterator-returned.

    Closes #388

•   Allow ending a pragma control with a semicolon. In this way, users can continue a pragma control with a reason for why it is used, as in # pylint: disable=old-style-class;reason=....

    Closes #449

•   --jobs can be used with --load-plugins now.

    Closes #456

•   Improve the performance of --jobs when dealing only with a package name.

    Closes #479

•   Don't emit an unused-wildcard-import when the imported name comes from another module and it is in fact a __future__ name.

•   The colorized reporter now works on Windows.

    Closes #96.

•   Remove pointless-except warning. It was previously disabled by default and it wasn't very useful.

    Closes #506.

•   Fix a crash on Python 3 related to the string checker, which crashed when it encountered a bytes string with a .format method called.

•   Don't warn about no-self-use for builtin properties.

•   Fix a false positive for bad-reversed-sequence, when a subclass of a dict provides a __reversed__ method.

•   Change the default no-docstring-rgx so missing-docstring isn't emitted for private functions.

•   Don't emit redefined-outer-name for __future__ directives.

    Closes #520.

•   Provide some hints for the bad-builtin message.

    Closes #522.

•   When checking for invalid arguments to a callable, in typecheck.py, look up for the __init__ in case the found __new__ comes from builtins.

    Since the __new__ comes from builtins, it will not have attached any information regarding what parameters it expects, so the check will be useless. Retrieving __init__ in that case will at least detect a couple of false negatives.

    Closes #429.

•   Don't emit no-member for classes with unknown bases.

    Since we don't know what those bases might add, we simply ignore the error in this case.

•   Lookup in the implicit metaclass when checking for no-member, if the class in question has an implicit metaclass, which is True for new style classes.

    Closes #438.

•   Add two new warnings, duplicate-bases and inconsistent-mro.

    duplicate-bases is emitted when a class has the same bases listed more than once in its bases definition, while inconsistent-mro is emitted when no sane mro hierarchy can be determined.

    Closes #526.

•   Remove interface-not-implemented warning.

    Closes #532.

•   Remove the rest of interface checks: interface-is-not-class, missing-interface-method, unresolved-interface. The reason is that its better to start recommending ABCs instead of the old Zope era of interfaces. One side effect of this change is that ignore-iface-methods becomes a noop, it's deprecated and it will be removed at some time.

•   Emit a proper deprecation warning for reporters.BaseReporter.add_message.

    The alternative way is to use handle_message. add_message will be removed in Pylint 1.6.

•   Added new module 'extensions' for optional checkers with the test directory 'test/extensions' and documentation file 'doc/extensions.rst'.

•   Added new checker 'extensions.check_docs' that verifies parameter documentation in Sphinx, Google, and Numpy style.

•   Detect undefined variable cases, where the "definition" of an undefined variable was in del statement. Instead of emitting used-before-assignment, which is totally misleading, it now emits undefined-variable.

    Closes #528.

•   Don't emit attribute-defined-outside-init and access-member-before-definition for mixin classes. Actual errors can occur in mixin classes, but this is controlled by the ignore-mixin-members option.

    Closes #412.

•   Improve the detection of undefined variables and variables used before assignment for variables used as default arguments to function, where the variable was first defined in the class scope.

    Closes #342 and issue #404.

•   Add a new warning, 'unexpected-special-method-signature', which is emitted when a special method (dunder method) doesn't have the expected signature, which can lead to actual errors in the application code.

    Closes #253.

•   Remove 'bad-context-manager' due to the inclusion of 'unexpected-special-method-signature'.

•   Don't emit no-name-in-module if the import is guarded by an ImportError, Exception or a bare except clause.

•   Don't emit no-member if the attribute access node is protected by an except handler, which handles AttributeError, Exception or it is a bare except.

•   Don't emit import-error if the import is guarded by an ImportError, Exception or a bare except clause.

•   Don't emit undefined-variable if the node is guarded by a NameError, Exception or bare except clause.

•   Add a new warning, 'using-constant-test', which is emitted when a conditional statement (If, IfExp) uses a test which is always constant, such as numbers, classes, functions etc. This is most likely an error from the user's part.

    Closes #524.

•   Don't emit 'raising-non-exception' when the exception has unknown bases. We don't know what those bases actually are and it's better to assume that the user knows what he is doing rather than emitting a message which can be considered a false positive.

•   Look for a .pylintrc configuration file in the current folder, if pylintrc is not found. Dotted pylintrc files will not be searched in the parents of the current folder, as it is done for pylintrc.

•   Add a new error, 'invalid-unary-type-operand', emitted when an unary operand is used on something which doesn't support that operation (for instance, using the unary bitwise inversion operator on an instance which doesn't implement __invert__).

•   Take in consideration differences between arguments of various type of functions (classmethods, staticmethods, properties) when checking for arguments-differ.

    Closes #548.

•   astroid.inspector was moved to pylint.pyreverse, since it belongs there and it doesn't need to be in astroid.

•   astroid.utils.LocalsVisitor was moved to pylint.pyreverse.LocalsVisitor.

•   pylint.checkers.utils.excepts_import_error was removed. Use pylint.chekcers.utils.error_of_type instead.

•   Don't emit undefined-all-variables for nodes which can't be inferred (YES nodes).

•   yield-outside-func is also emitted for yield from.

•   Add a new error, 'too-many-star-expressions', emitted when there are more than one starred expression (*x) in an assignment. The warning is emitted only on Python 3.

•   Add a new error, 'invalid-star-assignment-target', emitted when a starred expression (*x) is used as the lhs side of an assignment, as in *x = [1, 2]. This is not a SyntaxError on Python 3 though.

•   Detect a couple of objects which can't be base classes (bool, slice, range and memoryview, which weren't detected until now).

•   Add a new error for the Python 3 porting checker, import-star-module-level, which is used when a star import is detected in another scope than the module level, which is an error on Python 3. Using this will emit a SyntaxWarning on Python 2.

•   Add a new error, 'star-needs-assignment-target', emitted on Python 3 when a Starred expression (*x) is not used in an assignment target. This is not caught when parsing the AST on Python 3, so it needs to be a separate check.

•   Add a new error, 'unsupported-binary-operation', emitted when two a binary arithmetic operation is executed between two objects which don't support it (a number plus a string for instance). This is currently disabled, since the it exhibits way too many false positives, but it will be re-enabled as soon as possible.

•   New imported features from astroid into pyreverse: pyreverse.inspector.Project, pyreverse.inspector.project_from_files and pyreverse.inspector.interfaces.

    These were moved since they didn't belong in astroid.

•   Enable misplaced-future for Python 3.

    Closes #580.

•   Add a new error, 'nonlocal-and-global', which is emitted when a name is found to be both nonlocal and global in the same scope.

    Closes #581.

•   ignored-classes option can work with qualified names (ignored-classes=optparse.Values)

    Closes #297

•   ignored-modules can work with qualified names as well as with Unix pattern matching for recursive ignoring.

    Closes #244

•   Improve detection of relative imports in non-packages, as well as importing missing modules with a relative import from a package.

•   Don't emit no-init if not all the bases from a class are known.

    Closes #604.

•   --no-space-check option accepts empty-line as a possible option.

    Closes #541.

•   --generate-rcfile generates by default human readable symbols for the --disable option.

    Closes #608.

•   Improved the not-in-loop checker to properly detect more cases.

•   Add a new error, 'continue-in-finally', which is emitted when the continue keyword is found inside a finally clause, which is a SyntaxError.

•   The --zope flag is deprecated and it is slated for removal in Pylint 1.6.

    The reason behind this removal is the fact that it's a specialized flag and there are solutions for the original problem: use --generated-members with the members that causes problems when using Zope or add AST transforms tailored to the zope project.

    At the same time, --include-ids and --symbols will also be removed in Pylint 1.6.

    Closes #570.

•   missing-module-attribute was removed and the corresponding CLI option, required-attributes, which is slated for removal in Pylint 1.6.

•   missing-reversed-argument was removed.

    The reason behind this is that this kind of errors should be detected by the type checker for all the builtins and not as a special case for the reversed builtin. This will happen shortly in the future.

•   --comment flag is obsolete and it will be removed in Pylint 1.6.

•   --profile flag is obsolete and it will be removed in Pylint 1.6.

•   Add a new error, 'misplaced-bare-raise'.

    The error is used when a bare raise is not used inside an except clause. This can generate a RuntimeError in Python, if there are no active exceptions to be reraised. While it works in Python 2 due to the fact that the exception leaks outside of the except block, it's nevertheless a behaviour that a user shouldn't depend upon, since it's not obvious to the reader of the code what exception will be raised and it will not be compatible with Python 3 anyhow.

    Closes #633.

•   Bring logilab-common's ureports into pylint.reporters.

    With this change, we moved away from depending on logilab-common, having in Pylint all the components that were used from logilab-common. The API should be considered an implementation detail and can change at some point in the future.

    Closes #621.

•   reimported is emitted for reimported objects on the same line.

    Closes #639.

•   Abbreviations of command line options are not supported anymore.

    Using abbreviations for CLI options was never considered to be a feature of pylint, this fact being only a side effect of using optparse. As this was the case, using --load-plugin or other abbreviation for --load-plugins never actually worked, while it also didn't raise an error.

    Closes #424.

•   Add a new error, 'nonlocal-without-binding'

    The error is emitted on Python 3 when a nonlocal name is not bound to any variable in the parents scopes.

    Closes #582.

•

'deprecated-module' can be shown for modules which aren't
    available.

    Closes #362.

•   Don't consider a class abstract if its members can't be properly inferred.

    This fixes a false positive related to abstract-class-instantiated.

    Closes #648.

•   Add a new checker for the async features added by PEP 492.

•   Add a new error, 'yield-inside-async-function', emitted on Python 3.5 and upwards when the yield statement is found inside a new coroutine function (PEP 492).

•   Add a new error, 'not-async-context-manager', emitted when an async context manager block is used with an object which doesn't support this protocol (PEP 492).

•   Add a new convention warning, 'singleton-comparison', emitted when comparison to True, False or None is found.

•   Don't emit 'assigning-non-slot' for descriptors.

    Closes #652.

•   Add a new error, 'repeated-keyword', when a keyword argument is passed multiple times into a function call.

    This is similar with redundant-keyword-arg, but it's mildly different that it needs to be a separate error.

•   --enable=all can now be used.

    Closes #142.

•   Add a new convention message, 'misplaced-comparison-constant', emitted when a constant is placed in the left hand side of a comparison, as in '5 == func()'. This is also called Yoda condition, since the flow of code reminds of the Star Wars green character, conditions usually encountered in languages with variabile assignments in conditional statements.

•   Add a new convention message, 'consider-using-enumerate', which is emitted when code that uses range and len for iterating is encountered.

    Closes #684.

•   Added two new refactoring messages, 'no-classmethod-decorator' and 'no-staticmethod-decorator', which are emitted when a static method or a class method is declared without using decorators syntax.

    Closes #675.

  What's New In Pylint 1.4

  What's New in Pylint 1.4.3?

Release date: 2015-03-14

•   Remove three warnings: star-args, abstract-class-little-used, abstract-class-not-used. These warnings don't add any real value and they don't imply errors or problems in the code.

•   Added a new option for controlling the peephole optimizer in astroid. The option --optimize-ast will control the peephole optimizer, which is used to optimize a couple of AST subtrees. The current problem solved by the peephole optimizer is when multiple joined strings, with the addition operator, are encountered. If the numbers of such strings is high enough, Pylint will then fail with a maximum recursion depth exceeded error, due to its visitor architecture. The peephole just transforms such calls, if it can, into the final resulting string and this exhibit a problem, because the visit_binop method stops being called (in the optimized AST it will be a Const node).

  What's New in Pylint 1.4.2?

Release date: 2015-03-11

•   Don't require a docstring for empty modules.

    Closes #261

•   Fix a false positive with too-few-format-args string warning, emitted when the string format contained a normal positional argument ('{0}'), mixed with a positional argument which did an attribute access ('{0.__class__}').

    Closes #463

•   Take in account all the methods from the ancestors when checking for too-few-public-methods.

    Closes #471

•   Catch enchant errors and emit 'invalid-characters-in-docstring' when checking for spelling errors.

    Closes #469

•   Use all the inferred statements for the super-init-not-called check.

    Closes #389

•   Add a new warning, 'unichr-builtin', emitted by the Python 3 porting checker, when the unichr builtin is found.

    Closes #472

•   Add a new warning, 'intern-builtin', emitted by the Python 3 porting checker, when the intern builtin is found.

    Closes #473

•   Add support for editable installations.

•   The HTML output accepts the --msg-template option. Patch by Dan Goldsmith.

•   Add 'map-builtin-not-iterating' (replacing 'implicit-map-evaluation'), 'zip-builtin-not-iterating', 'range-builtin-not-iterating', and 'filter-builtin-not-iterating' which are emitted by --py3k when the appropriate built-in is not used in an iterating context (semantics taken from 2to3).

•   Add a new warning, 'unidiomatic-typecheck', emitted when an explicit typecheck uses type() instead of isinstance(). For example, type(x) == Y instead of isinstance(x, Y). Patch by Chris Rebert.

    Closes #299

•   Add support for combining the Python 3 checker mode with the --jobs flag (--py3k and --jobs).

    Closes #467

•   Add a new warning for the Python 3 porting checker, 'using-cmp-argument', emitted when the cmp argument for the list.sort or sorted builtin is encountered.

•   Make the --py3k flag commutative with the -E flag. Also, this patch fixes the leaks of error messages from the Python 3 checker when the errors mode was activated.

    Closes #437

  What's New in Pylint 1.4.1?

Release date: 2015-01-16

•   Look only in the current function's scope for bad-super-call.

    Closes #403

•   Check the return of properties when checking for not-callable.

    Closes #406

•   Warn about using the input() or round() built-ins for Python 3.

    Closes #411

•   Proper abstract method lookup while checking for abstract-class-instantiated.

    Closes #401

•   Use a mro traversal for finding abstract methods.

    Closes #415

•   Fix a false positive with catching-non-exception and tuples of exceptions.

•   Fix a false negative with raising-non-exception, when the raise used an uninferrable exception context.

•   Fix a false positive on Python 2 for raising-bad-type, when raising tuples in the form 'raise (ZeroDivisionError, None)'.

•   Fix a false positive with invalid-slots-objects, where the slot entry was a unicode string on Python 2.

    Closes #421

•   Add a new warning, 'redundant-unittest-assert', emitted when using unittest's methods assertTrue and assertFalse with constant value as argument. Patch by Vlad Temian.

•   Add a new JSON reporter, usable through -f flag.

•   Add the method names for the 'signature-differs' and 'argument-differs' warnings.

    Closes #433

•   Don't compile test files when installing.

•   Fix a crash which occurred when using multiple jobs and the files given as argument didn't exist at all.

  What's New in Pylint 1.4.0?

Release date: 2014-11-23

•   Added new options for controlling the loading of C extensions. By default, only C extensions from the stdlib will be loaded into the active Python interpreter for inspection, because they can run arbitrary code on import. The option --extension-pkg-whitelist can be used to specify modules or packages that are safe to load.

•   Change default max-line-length to 100 rather than 80

•   Drop BaseRawChecker class which were only there for backward compatibility for a while now

•   Don't try to analyze string formatting with objects coming from function arguments.

    Closes #373

•   Port source code to be Python 2/3 compatible. This drops the need for 2to3, but does drop support for Python 2.5.

•   Each message now comes with a confidence level attached, and can be filtered base on this level. This allows to filter out all messages that were emitted even though an inference failure happened during checking.

•   Improved presenting unused-import message.

    Closes #293

•   Add new checker for finding spelling errors. New messages: wrong-spelling-in-comment, wrong-spelling-in-docstring. New options: spelling-dict, spelling-ignore-words.

•   Add new '-j' option for running checks in sub-processes.

•   Added new checks for line endings if they are mixed (LF vs CRLF) or if they are not as expected. New messages: mixed-line-endings, unexpected-line-ending-format. New option: expected-line-ending-format.

•   'dangerous-default-value' no longer evaluates the value of the arguments, which could result in long error messages or sensitive data being leaked.

    Closes #282

•   Fix a false positive with string formatting checker, when encountering a string which uses only position-based arguments.

    Closes #285

•   Fix a false positive with string formatting checker, when using keyword argument packing.

    Closes #288

•   Proper handle class level scope for lambdas.

•   Handle 'too-few-format-args' or 'too-many-format-args' for format strings with both named and positional fields.

    Closes #286

•   Analyze only strings by the string format checker.

    Closes #287

•   Properly handle nested format string fields.

    Closes #294

•   Don't emit 'attribute-defined-outside-init' if the attribute was set by a function call in a defining method.

    Closes #192

•   Properly handle unicode format strings for Python 2.

    Closes #296

•   Don't emit 'import-error' if an import was protected by a try-except, which excepted ImportError.

•   Fix an 'unused-import' false positive, when the error was emitted for all the members imported with 'from import' form.

    Closes #304

•   Don't emit 'invalid-name' when assigning a name in an ImportError handler.

    Closes #302

•   Don't count branches from nested functions.

•   Fix a false positive with 'too-few-format-args', when the format strings contains duplicate manual position arguments.

    Closes #310

•   fixme regex handles comments without spaces after the hash.

    Closes #311

•   Don't emit 'unused-import' when a special object is imported (__all__, __doc__ etc.).

    Closes #309

•   Look in the metaclass, if defined, for members not found in the current class.

    Closes #306

•   Don't emit 'protected-access' if the attribute is accessed using a property defined at the class level.

•   Detect calls of the parent's __init__, through a binded super() call.

•   Check that a class has an explicitly defined metaclass before emitting 'old-style-class' for Python 2.

•   Emit 'catching-non-exception' for non-class nodes.

    Closes #303

•   Order of reporting is consistent.

•   Add a new warning, 'boolean-datetime', emitted when an instance of 'datetime.time' is used in a boolean context.

    Closes #239

•   Fix a crash which occurred while checking for 'method-hidden', when the parent frame was something different than a function.

•   Generate html output for missing files.

    Closes #320

•   Fix a false positive with 'too-many-format-args', when the format string contains mixed attribute access arguments and manual fields.

    Closes #322

•   Extend the cases where 'undefined-variable' and 'used-before-assignment' can be detected.

    Closes #291

•   Add support for customising callback identifiers, by adding a new '--callbacks' command line option.

    Closes #326

•   Add a new warning, 'logging-format-interpolation', emitted when .format() string interpolation is used within logging function calls.

•   Don't emit 'unbalanced-tuple-unpacking' when the rhs of the assignment is a variable length argument.

    Closes #329

•   Add a new warning, 'inherit-non-class', emitted when a class inherits from something which is not a class.

    Closes #331

•   Fix another false positives with 'undefined-variable', where the variable can be found as a class assignment and used in a function annotation.

    Closes #342

•   Handle assignment of the string format method to a variable.

    Closes #351

•   Support wheel packaging format for PyPi.

    Closes #334

•   Check that various built-ins that do not exist in Python 3 are not used: apply, basestring, buffer, cmp, coerce, execfile, file, long raw_input, reduce, StandardError, unicode, reload and xrange.

•   Warn for magic methods which are not used in any way in Python 3: __coerce__, __delslice__, __getslice__, __setslice__, __cmp__, __oct__, __nonzero__ and __hex__.

•   Don't emit 'assigning-non-slot' when the assignment is for a property.

    Closes #359

•   Fix for regression: '{path}' was no longer accepted in '--msg-template'.

•   Report the percentage of all messages, not just for errors and warnings.

    Closes #319

•   'too-many-public-methods' is reported only for methods defined in a class, not in its ancestors.

    Closes #248

•   'too-many-lines' disable pragma can be located on any line, not only the first.

    Closes #321

•   Warn in Python 2 when an import statement is found without a corresponding from __future__ import absolute_import.

•   Warn in Python 2 when a non-floor division operation is found without a corresponding from __future__ import division.

•   Add a new option, 'exclude-protected', for excluding members from the protected-access warning.

    Closes #48

•   Warn in Python 2 when using dict.iter*(), dict.view*(); none of these methods are available in Python 3.

•   Warn in Python 2 when calling an object's next() method; Python 3 uses __next__() instead.

•   Warn when assigning to __metaclass__ at a class scope; in Python 3 a metaclass is specified as an argument to the 'class' statement.

•   Warn when performing parameter tuple unpacking; it is not supported in Python 3.

•   'abstract-class-instantiated' is also emitted for Python 2. It was previously disabled.

•   Add 'long-suffix' error, emitted when encountering the long suffix on numbers.

•   Add support for disabling a checker, by specifying an 'enabled' attribute on the checker class.

•   Add a new CLI option, --py3k, for enabling Python 3 porting mode. This mode will disable all other checkers and will emit warnings and errors for constructs which are invalid or removed in Python 3.

•   Add 'old-octal-literal' to Python 3 porting checker, emitted when encountering octals with the old syntax.

•   Add 'implicit-map-evaluation' to Python 3 porting checker, emitted when encountering the use of map builtin, without explicit evaluation.

  What's New In Pylint 1.3

Release date: 2014-07-26

•   Allow hanging continued indentation for implicitly concatenated strings.

    Closes #232.

•   Pylint works under Python 2.5 again, and its test suite passes.

•   Fix some false positives for the cellvar-from-loop warnings.

    Closes #233.

•   Return new astroid class nodes when the inferencer can detect that that result of a function invocation on a type (like type or abc.ABCMeta) is requested.

    Closes #205.

•   Emit 'undefined-variable' for undefined names when using the Python 3 metaclass= argument.

•   Checkers respect priority now.

    Closes #229

•   Fix a false positive regarding W0511.

    Closes #149.

•   Fix unused-import false positive with Python 3 metaclasses

    Closes #143

•   Don't warn with 'bad-format-character' when encountering the 'a' format on Python 3.

•   Add multiple checks for PEP 3101 advanced string formatting: 'bad-format-string', 'missing-format-argument-key', 'unused-format-string-argument', 'format-combined-specification', 'missing-format-attribute' and 'invalid-format-index'.

•   Issue broad-except and bare-except even if the number of except handlers is different than 1.

    Closes #113

•   Issue attribute-defined-outside-init for all cases, not just for the last assignment.

    Closes #262

•   Emit 'not-callable' when calling properties.

    Closes #268.

•   Fix a false positive with unbalanced iterable unpacking, when encountering starred nodes.

    Closes #273.

•   Add new checks, 'invalid-slice-index' and 'invalid-sequence-index' for invalid sequence and slice indices.

•   Add 'assigning-non-slot' warning, which detects assignments to attributes not defined in slots.

•   Don't emit 'no-name-in-module' for ignored modules.

    Closes #223.

•   Fix an 'unused-variable' false positive, where the variable is assigned through an import.

    Closes #196.

•   Definition order is considered for classes, function arguments and annotations.

    Closes #257.

•   Don't emit 'unused-variable' when assigning to a nonlocal.

    Closes #275.

•   Do not let ImportError propagate from the import checker, leading to crash in some namespace package related cases.

    Closes #203.

•   Don't emit 'pointless-string-statement' for attribute docstrings.

    Closes #193.

•   Use the proper mode for pickle when opening and writing the stats file.

    Closes #148.

•   Don't emit hidden-method message when the attribute has been monkey-patched, you're on your own when you do that.

•   Only emit attribute-defined-outside-init for definition within the same module as the offended class, avoiding to mangle the output in some cases.

•   Don't emit 'unnecessary-lambda' if the body of the lambda call contains call chaining.

    Closes #243.

•   Don't emit 'missing-docstring' when the actual docstring uses .format.

    Closes #281.

  What's New In Pylint 1.2

Release date: 2014-04-30

•   Restore the ability to specify the init-hook option via the configuration file, which was accidentally broken in 1.2.0.

•   Add a new warning [bad-continuation] for badly indented continued lines.

•   Emit [assignment-from-none] when the function contains bare returns.

    Closes BitBucket #191

•   Added a new warning for closing over variables that are defined in loops.

    Closes BitBucket #176

•   Do not warn about u escapes in string literals when Unicode literals are used for Python 2.*.

    Closes BitBucket #151

•   Extend the checking for unbalanced-tuple-unpacking and unpacking-non-sequence to instance attribute unpacking as well.

•   Fix explicit checking of python script (1.2 regression)

    Closes #219

•   Restore --init-hook, renamed accidentally into --init-hooks in 1.2.0

    Closes #211

•   Add 'indexing-exception' warning, which detects that indexing an exception occurs in Python 2 (behaviour removed in Python 3).

  What's New in Pylint 1.2.0?

Release date: 2014-04-18

•   Pass the current python paths to pylint process when invoked via epylint.

    Closes BitBucket #133.

•   Add -i / --include-ids and -s / --symbols back as completely ignored options.

    Closes BitBucket #180.

•   Extend the number of cases in which logging calls are detected.

    Closes BitBucket #182.

•   Improve pragma handling to not detect pylint:* strings in non-comments.

    Closes BitBucket #79.

•   Do not crash with UnknownMessage if an unknown message ID/name appears in disable or enable in the configuration. Patch by Cole Robinson.

    Closes BitBucket #170

•   Add new warning 'eval-used', checking that the builtin function eval was used.

•   Make it possible to show a naming hint for invalid name by setting include-naming-hint. Also make the naming hints configurable.

    Closes BitBucket #138

•   Added support for enforcing multiple, but consistent name styles for different name types inside a single module; based on a patch written by morbo@google.com.

•   Also warn about empty docstrings on overridden methods; contributed by sebastianu@google.com.

•   Also inspect arguments to constructor calls, and emit relevant warnings; contributed by sebastianu@google.com.

•   Added a new configuration option logging-modules to make the list of module names that can be checked for 'logging-not-lazy' et. al. configurable; contributed by morbo@google.com.

•   ensure init-hooks is evaluated before other options, notably load-plugins

    Closes #166

•   Python 2.5 support restored: fixed small issues preventing pylint to run on python 2.5.

    Closes BitBucket #50 Closes BitBucket #62

•   pylint doesn't crash when looking for used-before-assignment in context manager assignments.

    Closes BitBucket #128

•   Add new warning, 'bad-reversed-sequence', for checking that the reversed() builtin receive a sequence (implements __getitem__ and __len__, without being a dict or a dict subclass) or an instance which implements __reversed__.

•   Mark file as a bad function when using python2

    Closes #8

•   Add new warning 'bad-exception-context', checking that raise ... from ... uses a proper exception context (None or an exception).

•   Enhance the check for 'used-before-assignment' to look for 'nonlocal' uses.

•   Emit 'undefined-all-variable' if a package's __all__ variable contains a missing submodule.

    Closes #126

•   Add a new warning 'abstract-class-instantiated' for checking that abstract classes created with abc module and with abstract methods are instantiated.

•   Do not warn about 'return-arg-in-generator' in Python 3.3+.

•   Do not warn about 'abstract-method' when the abstract method is implemented through assignment

    Closes #155

•   Improve cyclic import detection in the case of packages, patch by Buck Golemon

•   Add new warnings for checking proper class __slots__: invalid-slots-object and invalid-slots.

•   Search for rc file in ~/.config/pylintrc if ~/.pylintrc doesn't exists

    Closes #121

•   Don't register the new style checker w/ python >= 3

•   Fix unused-import false positive w/ augment assignment

    Closes #78

•   Fix access-member-before-definition false negative wrt aug assign

    Closes #164

•   Do not attempt to analyze non python file, e.g. .so file

    Closes #122

  What's New In Pylint 1.1

Release date: 2013-12-22

•   Add new check for use of deprecated pragma directives "pylint:disable-msg" or "pylint:enable-msg" (I0022, deprecated-pragma) which was previously emitted as a regular warn().

•   Avoid false used-before-assignment for except handler defined identifier used on the same line.

    Closes #111

•   Combine 'no-space-after-operator', 'no-space-after-comma' and 'no-space-before-operator' into a new warning 'bad-whitespace'.

•   Add a new warning 'superfluous-parens' for unnecessary parentheses after certain keywords.

•   Fix a potential crash in the redefine-in-handler warning if the redefined name is a nested getattr node.

•   Add a new option for the multi-statement warning to allow single-line if statements.

•   Add 'bad-context-manager' error, checking that '__exit__' special method accepts the right number of arguments.

•   Run pylint as a python module 'python -m pylint' (Anatoly Techtonik).

•   Check for non-exception classes inside an except clause.

•   epylint support options to give to pylint after the file to analyze and have basic input validation, patches provided by felipeochoa and Brian Lane.

    Closes BitBucket #53 Closes BitBucket #54

•   Added a new warning, 'non-iterator-returned', for non-iterators returned by '__iter__'.

•   Add new checks for unpacking non-sequences in assignments (unpacking-non-sequence) as well as unbalanced tuple unpacking (unbalanced-tuple-unpacking).

•   useless-else-on-loop not emitted if there is a break in the else clause of inner loop.

    Closes #117

•   don't mark input as a bad function when using python3.

    Closes #110

•   badly-implemented-container caused several problems in its current implementation. Deactivate it until we have something better.

    Refs #112

•   Use attribute regexp for properties in python3, as in python2

•   Create the PYLINTHOME directory when needed, it might fail and lead to spurious warnings on import of pylint.config.

•   Fix setup.py so that pylint properly install on Windows when using python3

•   Various documentation fixes and enhancements

•   Fix a false-positive trailing-whitespace on Windows

    Closes #55

  What's New In Pylint 1.0

Release date: 2013-08-06

•   Add check for the use of 'exec' function

•   New --msg-template option to control output, deprecating "msvc" and "parseable" output formats as well as killing --include-ids and --symbols options

•   Do not emit [fixme] for every line if the config value 'notes' is empty, but [fixme] is enabled.

•   Emit warnings about lines exceeding the column limit when those lines are inside multiline docstrings.

•   Do not double-check parameter names with the regex for parameters and inline variables.

•   Added a new warning missing-final-newline (C0304) for files missing the final newline.

•   Methods that are decorated as properties are now treated as attributes for the purposes of name checking.

•   Names of derived instance class member are not checked any more.

•   Names in global statements are now checked against the regular expression for constants.

•   For toplevel name assignment, the class name regex will be used if pylint can detect that value on the right-hand side is a class (like collections.namedtuple()).

•   Simplified invalid-name message

•   Added a new warning invalid-encoded-data (W0512) for files that contain data that cannot be decoded with the specified or default encoding.

•   New warning bad-open-mode (W1501) for calls to open (or file) that specify invalid open modes (Original implementation by Sasha Issayev).

•   New warning old-style-class (C1001) for classes that do not have any base class.

•   Add new name type 'class_attribute' for attributes defined in class scope. By default, allow both const and variable names.

•   New warning trailing-whitespace (C0303) that warns about trailing whitespace.

•   Added a new warning unpacking-in-except (W0712) about unpacking exceptions in handlers, which is unsupported in Python 3.

•   Add a configuration option for missing-docstring to optionally exempt short functions/methods/classes from the check.

•   Add the type of the offending node to missing-docstring and empty-docstring.

•   New utility classes for per-checker unittests in testutils.py

•   Do not warn about redefinitions of variables that match the dummy regex.

•   Do not treat all variables starting with _ as dummy variables, only _ itself.

•   Make the line-too-long warning configurable by adding a regex for lines for with the length limit should not be enforced

•   Do not warn about a long line if a pylint disable option brings it above the length limit

•   Do not flag names in nested with statements as undefined.

•   Added a new warning 'old-raise-syntax' for the deprecated syntax raise Exception, args

•   Support for PEP 3102 and new missing-kwoa (E1125) message for missing mandatory keyword argument

    Closes Logilab #107788

•   Fix spelling of max-branchs option, now max-branches

•   Added a new base class and interface for checkers that work on the tokens rather than the syntax, and only tokenize the input file once.

•   Follow astng renaming to astroid

•   Check for unbalanced unpacking in assignments

    Closes BitBucket #37

•   Fix incomplete-protocol false positive for read-only containers like tuple

    Closes BitBucket #25

•   Fix False positive E1003 on Python 3 for argument-less super()

    Closes BitBucket #16

•   Put back documentation in source distribution

    Closes BitBucket #6

•   epylint shouldn't hang anymore when there is a large output on pylint'stderr

    Closes BitBucket #15

•   Fix epylint w/ python3

    Closes BitBucket #7

•   Remove string module from the default list of deprecated modules

    Closes BitBucket #3

  0.x

From pylint's beginning to pylint 2.14.0 included, we had a changelog that contained all nontrivial changes to Pylint, including changes that were not user facing, i.e. change that might interest you only if you're a developer working on pylint or pylint plugins or an open-source historian.

Ticket numbers are almost always internal to Logilab, some come from bitbucket.

  What's New in Pylint 0.28.0?

Release date: 2013-04-25

•   bitbucket #1: fix "dictionary changed size during iteration" crash

•   #74013: new E1310[bad-str-strip-call] message warning when a call to a {l,r,}strip method contains duplicate characters (patch by Torsten Marek)

•   #123233: new E0108[duplicate-argument-name] message reporting duplicate argument names

•   #81378: emit W0120[useless-else-on-loop] for loops without break

•   #124660: internal dependencies should not appear in external dependencies report

•   #124662: fix name error causing crash when symbols are included in output messages

•   #123285: apply pragmas for warnings attached to lines to physical source code lines

•   #123259: do not emit E0105 for yield expressions inside lambdas

•   #123892: don't crash when attempting to show source code line that can't be encoded with the current locale settings

•   Simplify checks for dangerous default values by unifying tests for all different mutable compound literals.

•   Improve the description for E1124[redundant-keyword-arg]

  What's New in Pylint 0.27.0?

Release date: 2013-02-26

•   #20693: replace pylint.el by Ian Eure version (patch by J.Kotta)

•   #105327: add support for --disable=all option and deprecate the 'disable-all' inline directive in favour of 'skip-file' (patch by A.Fayolle)

•   #110840: add messages I0020 and I0021 for reporting of suppressed messages and useless suppression pragmas. (patch by Torsten Marek)

•   #112728: add warning E0604 for non-string objects in __all__ (patch by Torsten Marek)

•   #120657: add warning W0110/deprecated-lambda when a map/filter of a lambda could be a comprehension (patch by Martin Pool)

•   #113231: logging checker now looks at instances of Logger classes in addition to the base logging module. (patch by Mike Bryant)

•   #111799: don't warn about octal escape sequence, but warn about o which is not octal in Python (patch by Martin Pool)

•   #110839: bind <F5> to Run button in pylint-gui

•   #115580: fix erroneous W0212 (access to protected member) on super call (patch by Martin Pool)

•   #110853: fix a crash when an __init__ method in a base class has been created by assignment rather than direct function definition (patch by Torsten Marek)

•   #110838: fix pylint-gui crash when include-ids is activated (patch by Omega Weapon)

•   #112667: fix emission of reimport warnings for mixed imports and extend the testcase (patch by Torsten Marek)

•   #112698: fix crash related to non-inferable __all__ attributes and invalid __all__ contents (patch by Torsten Marek)

•   Python 3 related fixes:

•

#110213: fix import of checkers broken with python 3.3, causing
    "No such message id W0704" breakage

•   #120635: redefine cmp function used in pylint.reporters

•   Include full warning id for I0020 and I0021 and make sure to flush warnings after each module, not at the end of the pylint run. (patch by Torsten Marek)

•   Changed the regular expression for inline options so that it must be preceded by a # (patch by Torsten Marek)

•   Make dot output for import graph predictable and not depend on ordering of strings in hashes. (patch by Torsten Marek)

•   Add hooks for import path setup and move pylint's sys.path modifications into them. (patch by Torsten Marek)

  What's New in Pylint 0.26.0?

Release date: 2012-10-05

•   #106534: add --ignore-imports option to code similarity checking and 'symilar' command line tool (patch by Ry4an Brase)

•   #104571: check for anomalous backslash escape, introducing new W1401 and W1402 messages (patch by Martin Pool)

•   #100707: check for boolop being used as exception class, introducing new W0711 message (patch by Tim Hatch)

•   #4014: improve checking of metaclass methods first args, introducing new C0204 message (patch by lothiraldan@gmail.com finalized by sthenault)

•   #4685: check for consistency of a module's __all__ variable, introducing new E0603 message

•   #105337: allow custom reporter in output-format (patch by Kevin Jing Qiu)

•   #104420: check for protocol completeness and avoid false R0903 (patch by Peter Hammond)

•   #100654: fix grammatical error for W0332 message (using 'l' as long int identifier)

•   #103656: fix W0231 false positive for missing call to object.__init__ (patch by lothiraldan@gmail.com)

•   #63424: fix similarity report disabling by properly renaming it to RP0801

•   #103949: create a console_scripts entry point to be used by easy_install, buildout and pip

•   fix cross-interpreter issue (non compatible access to __builtins__)

•   stop including tests files in distribution, they causes crash when installed with python3 (#72022, #82417, #76910)

  What's New in Pylint 0.25.2?

Release date: 2012-07-17

•   #93591: Correctly emit warnings about clobbered variable names when an except handler contains a tuple of names instead of a single name. (patch by tmarek@google.com)

•   #7394: W0212 (access to protected member) not emitted on assignments (patch by lothiraldan@gmail.com)

•   #18772; no prototype consistency check for mangled methods (patch by lothiraldan@gmail.com)

•   #92911: emit W0102 when sets are used as default arguments in functions (patch by tmarek@google.com)

•   #77982: do not emit E0602 for loop variables of comprehensions used as argument values inside a decorator (patch by tmarek@google.com)

•   #89092: don't emit E0202 (attribute hiding a method) on @property methods

•   #92584: fix pylint-gui crash due to internal API change

•   #87192: fix crash when decorators are accessed through more than one dot (for instance @a.b is fine, @a.b.c crash)

•   #88914: fix parsing of --generated-members options, leading to crash when using a regexp value set

•   fix potential crashes with utils.safe_infer raising InferenceError

  What's New in Pylint 0.25.1?

Release date: 2011-12-08

•   #81078: Warn if names in exception handlers clobber overwrite existing names (patch by tmarek@google.com)

•   #81113: Fix W0702 messages appearing with the wrong line number. (patch by tmarek@google.com)

•   #50461, #52020, #51222: Do not issue warnings when using 2.6's property.setter/deleter functionality (patch by dneil@google.com)

•   #9188, #4024: Do not trigger W0631 if a loop variable is assigned in the else branch of a for loop.

  What's New in Pylint 0.25.0?

Release date: 2011-10-7

•   #74742: make allowed name for first argument of class method configurable (patch by Google)

•   #74087: handle case where inference of a module return YES; this avoid some cases of "TypeError: '_Yes' object does not support indexing" (patch by Google)

•   #74745: make "too general" exception names configurable (patch by Google)

•   #74747: crash occurs when lookup up a special attribute in class scope (patch by google)

•   #76920: crash if on e.g. "pylint --rcfile" (patch by Torsten Marek)

•   #77237: warning for E0202 may be very misleading

•   #73941: HTML report messages table is badly rendered

  What's New in Pylint 0.24.0?

Release date: 2011-07-18

•   #69738: add regular expressions support for "generated-members"

•   ids of logging and string_format checkers have been changed: logging: 65 -> 12, string_format: 99 -> 13 Also add documentation to say that ids of range 1-50 shall be reserved to pylint internal checkers

•   #69993: Additional string format checks for logging module: check for missing arguments, too many arguments, or invalid string formats in the logging checker module. Contributed by Daniel Arena

•   #69220: add column offset to the reports. If you've a custom reporter, this change may break it has now location gain a new item giving the column offset.

•   #60828: Fix false positive in reimport check

•   #70495: absolute imports fail depending on module path (patch by Jacek Konieczny)

•   #22273: Fix --ignore option documentation to match reality

  What's New in Pylint 0.23.0?

Release date: 2011-01-11

•   documentation update, add manpages

•   several performance improvements

•   finalize python3 support

•   new W0106 warning 'Expression "%s" is assigned to nothing'

•   drop E0501 and E0502 messages about wrong source encoding: not anymore interesting since it's a syntax error for python >= 2.5 and we now only support this python version and above.

•   don't emit W0221 or W0222 when methods as variable arguments (e.g. *arg and/or **args). Patch submitted by Charles Duffy.

  What's New in Pylint 0.22.0?

Release date: 2010-11-15

•   python versions: minimal python3.x support; drop python < 2.5 support

  What's New in Pylint 0.21.4?

Release date: 2010-10-27

•   fix #48066: pylint crashes when redirecting output containing non-ascii characters

•   fix #19799: "pylint -blah" exit with status 2

•   update documentation

  What's New in Pylint 0.21.3?

Release date: 2010-09-28

•   restored python 2.3 compatibility. Along with logilab-astng 0.21.3 and logilab-common 0.52, this will much probably be the latest release supporting python < 2.5.

  What's New in Pylint 0.21.2?

Release date: 2010-08-26

•   fix #36193: import checker raise exception on cyclic import

•   fix #28796: regression in --generated-members introduced pylint 0.20

•   some documentation cleanups

  What's New in Pylint 0.21.1?

Release date: 2010-06-04

•   fix #28962: pylint crash with new options, due to missing stats data while writing the Statistics by types report

•   updated man page to 0.21 or greater command line usage (fix debian #582494)

  What's New in Pylint 0.21.0?

Release date: 2010-05-11

•   command line updated (closes #9774, #9787, #9992, #22962):

•   all enable-* / disable-* options have been merged into --enable / --disable

•   BACKWARD INCOMPATIBLE CHANGE: short name of --errors-only becomes -E, -e being affected to --enable

•   pylint --help output much simplified, with --long-help available to get the complete one

•   revisited gui, thanks to students from Toronto university (they are great contributors to this release!)

•   fix #21591: html reporter produces no output if reports is set to 'no'

•   fix #4581: not Missing docstring (C0111) warning if a method is overridden

•   fix #4683: Non-ASCII characters count double if utf8 encode

•   fix #9018: when using defining-attr-method, method order matters

•   fix #4595: Comma not followed by a space should not occurs on trailing comma in list/tuple/dict definition

•   fix #22585: [Patch] fix man warnings for pyreverse.1 manpage

•   fix #20067: AttributeError: 'NoneType' object has no attribute 'name' with with

  What's New in Pylint 0.20.0?

Release date: 2010-03-01

•   fix #19498: fix windows batch file

•   fix #19339: pylint.el : non existing py-mod-map (closes Debian Bug report logs - #475939)

•   implement #18860, new W0199 message on assert (a, b)

•   implement #9776, 'W0150' break or return statement in finally block may swallow exception.

•   fix #9263, __init__ and __new__ are checked for unused arguments

•   fix #20991, class scope definitions ignored in a genexpr

•   fix #5975, Abstract intermediate class not recognized as such

•   fix #5977, yield and return statement have their own counters, no more R0911 (Too many return statements) when a function have many yield stamtements

•   implement #5564, function / method arguments with leading "_" are ignored in arguments / local variables count.

•   implement #9982, E0711 specific error message when raising NotImplemented

•   remove --cache-size option

  What's New in Pylint 0.19.0?

Release date: 2009-12-18

•   implement #18947, #5561: checker for function arguments

•   include James Lingard string format checker

•   include simple message (ids) listing by Vincent Ferotin (#9791)

•   --errors-only does not hide fatal error anymore

•   include james Lingard patches for ++/-- and duplicate key in dicts

•   include James Lingard patches for function call arguments checker

•   improved Flymake code and doc provided by Derek Harland

•   refactor and fix the imports checker

•   fix #18862: E0601 false positive with lambda functions

•   fix #8764: More than one statement on a single line false positive with try/except/finally

•   fix #9215: false undefined variable error in lambda function

•   fix for w0108 false positive (Nathaniel)

•   fix test/fulltest.sh

•   #5821 added a utility function to run pylint in another process (patch provide by Vincent Ferotin)

  What's New in Pylint 0.18.0?

Release date: 2009-03-25

•   tests ok with python 2.4, 2.5, 2.6. 2.3 not tested

•   fix #8687, W0613 false positive on inner function

•   fix #8350, C0322 false positive on multi-line string

•   fix #8332: set E0501 line no to the first line where non ascii character has been found

•   avoid some E0203 / E0602 false negatives by detecting respectively AttributeError / NameError

•   implements #4037: don't issue W0142 (* or ** magic) when they are barely passed from /* arguments

•   complete #5573: more complete list of special methods, also skip W0613 for python internal method

•   don't show information messages by default

•   integration of Yuen Ho Wong's patches on Emacs lisp files

  What's New in Pylint 0.17.0?

Release date: 2009-03-19

•   semicolon check : move W0601 to W0301

•   remove rpython : remove all rpython checker, modules and tests

•   astng 0.18 compatibility: support for _ast module modifies interfaces

  What's New in Pylint 0.16.0?

Release date: 2009-01-28

•   change [en|dis]able-msg-cat options: only accept message categories identified by their first letter (e.g. IRCWEF) without the need for comma as separator

•   add epylint.bat script to fix Windows installation

•   setuptools/easy_install support

•   include a modified version of Maarten ter Huurne patch to avoid W0613 warning on arguments from overridden method

•   implement #5575 drop dumb W0704 message) by adding W0704 to ignored messages by default

•   new W0108 message, checking for suspicious lambda (provided by Nathaniel Manista)

•   fix W0631, false positive reported by Paul Hachmann

•   fix #6951: false positive with W0104

•   fix #6949

•   patches by Mads Kiilerich:

•   implement #4691, make pylint exits with a non zero return status if any messages other then Information are issued

•   fix #3711, #5626 (name resolution bug w/ decorator and class members)

•   fix #6954

  What's New in Pylint 0.15.2?

Release date: 2008-10-13

•   fix #5672: W0706 weirdness ( W0706 removed )

•   fix #5998: documentation points to wrong url for mailing list

•   fix #6022: no error message on wrong module names

•   fix #6040: pytest doesn't run test/func_test.py

  What's New in Pylint 0.15.1?

Release date: 2008-09-15

•   fix #4910: default values are missing in manpage

•   fix #5991: missing files in 0.15.0 tarball

•   fix #5993: epylint should work with python 2.3

  What's New in Pylint 0.15.0?

Release date: 2008-09-10

•   include pyreverse package and class diagram generation

•   included Stefan Rank's patch to deal with 2.4 relative import

•   included Robert Kirkpatrick's tutorial and typos fixes

•   fix bug in reenabling message

•   fix #2473: invoking pylint on __init__.py (hopefully)

•   typecheck: acquired-members option has been dropped in favor of the more generic generated-members option. If the zope option is set, the behaviour is now to add some default values to generated-members.

•   Flymake integration: added bin/epylint and elisp/pylint-flymake.el

  What's New in Pylint 0.14.0?

Release date: 2008-01-14

•   fix #3733: Messages (dis)appear depending on order of file names

•   fix #4026: pylint.el should require compile

•   fix a bug in colorized reporter, spotted by Dave Borowitz

•   applied patch from Stefan Rank to avoid W0410 false positive when multiple "from __future__" import statements

•   implement #4012: flag back tick as deprecated (new W0333 message)

•   new ignored-class option on typecheck checker allowing to skip members checking based on class name (patch provided by Thomas W Barr)

  What's New in Pylint 0.13.2?

Release date: 2007-06-07

•   fix disable-checker option so that it won't accidentally enable the rpython checker which is disabled by default

•   added note about the gedit plugin into documentation

  What's New in Pylint 0.13.1?

Release date: 2007-03-02

•   fix some unexplained 0.13.0 packaging issue which led to a bunch of files missing from the distribution

  What's New in Pylint 0.13.0?

Release date: 2007-02-28

•   new RPython (Restricted Python) checker for PyPy fellow or people wanting to get a compiled version of their python program using the translator of the PyPy project. For more information about PyPy or RPython, visit https://www.pypy.org, previously codespeak.net/pypy/

•   new E0104 and E0105 messages introduced to respectively warn about "return" and "yield" outside function or method

•   new E0106 message when "yield" and "return something" are mixed in a function or method

•   new W0107 message for unnecessary pass statement

•   new W0614 message to differentiate between unused import X and unused from X import * (#3209, patch submitted by Daniel Drake)

•   included Daniel Drake's patch to have a different message E1003 instead of E1001 when a missing member is found but an inference failure has been detected

•   msvs reporter for Visual Studio line number reporting (#3285)

•   allow disable-all option inline (#3218, patch submitted by Daniel Drake)

•   --init-hook option to call arbitrary code necessary to set environment (e.g. sys.path) (#3156)

•   One more Daniel's patch fixing a command line option parsing problem, this'll definitely be the DDrake release :)

•   fix #3184: crashes on "return" outside function

•   fix #3205: W0704 false positive

•   fix #3123: W0212 false positive on static method

•   fix #2485: W0222 false positive

•   fix #3259: when a message is explicitly enabled, check the checker emitting it is enabled

  What's New in Pylint 0.12.2?

Release date: 2006-11-23

•   fix #3143: W0233 bug w/ YES objects

•   fix #3119: Off-by-one error counting lines in a file

•   fix #3117: ease sys.stdout overriding for reporters

•   fix #2508: E0601 false positive with lambda

•   fix #3125: E1101 false positive and a message duplication. Only the last part is actually fixed since the initial false positive is due to dynamic setting of attributes on the decimal.Context class.

•   fix #3149: E0101 false positives and introduced E0100 for generator __init__ methods

•   fixed some format checker false positives

  What's New in Pylint 0.12.1?

Release date: 2006-09-25

•   fixed python >= 2.4 format false positive with multiple lines statement

•   fixed some 2.5 issues

•   fixed generator expression scope bug (depends on astng 0.16.1)

•   stop requiring __revision__

  What's New in Pylint 0.12.0?

Release date: 2006-08-10

•   usability changes:

•   parseable, html and color options are now handled by a single output-format option

•   enable-<checkerid> and disable-all options are now handled by two (exclusive) enable-checker and disable-checker options taking a comma separated list of checker names as value

•   renamed debug-mode option to errors-only

•   started a reference user manual

•   new W0212 message for access to protected member from client code (Closes #14081)

•   new W0105 and W0106 messages extracted from W0104 (statement seems to have no effect) respectively when the statement is actually string (that's sometimes used instead of comments for documentation) or an empty statement generated by a useless semicolon

•   reclassified W0302 to C0302

•   fix so that global messages are not anymore connected to the last analyzed module (Closes #10106)

•   fix some bugs related to local disabling of messages

•   fix cr/lf pb when generating the rc file on windows platforms

  What's New in Pylint 0.11.0?

Release date: 2006-04-19

•   fix crash caused by the exceptions checker in some case

•   fix some E1101 false positive with abstract method or classes defining __getattr__

•   dirty fix to avoid "_socketobject" has not "connect" member. The actual problem is that astng isn't able to understand the code used to create socket.socket object with exec

•   added an option in the similarity checker to ignore docstrings, enabled by default

•   included patch from Benjamin Niemann to allow block level enabling/disabling of messages

  What's New in Pylint 0.10.0?

Release date: 2006-03-06

•   WARNING, this release include some configuration changes (see below), so you may have to check and update your own configuration file(s) if you use one

•   this release require the 0.15 version of astng or superior (it will save you a lot of pylint crashes...)

•   W0705 has been reclassified to E0701, and is now detecting more inheriting problem, and a false positive when empty except clause is following an Exception catch has been fixed (Closes #10422)

•   E0212 and E0214 (metaclass/class method should have mcs/cls as first argument have been reclassified to C0202 and C0203 since this not as well established as "self" for instance method (E0213)

•   W0224 has been reclassified into F0220 (failed to resolve interfaces implemented by a class)

•   a new typecheck checker, introducing the following checks:

•   E1101, access to nonexistent member (implements #10430), remove the need of E0201 and so some options has been moved from the classes checker to this one

•   E1102, calling a non callable object

•   E1111 and W1111 when an assignment is done on a function call but the inferred function returns None (implements #10431)

•   change in the base checker:

•   checks module level and instance attribute names (new const-rgx and attr-rgx configuration option) (implements #10209 and #10440)

•   list comprehension and generator expression variables have their own regular expression (the inlinevar-rgx option) (implements #9146)

•   the C0101 check with its min-name-length option has been removed (this can be specified in the regxp after all...)

•   W0103 and W0121 are now handled by the variables checker (W0103 is now W0603 and W0604 has been split into different messages)

•   W0131 and W0132 messages have been reclassified to C0111 and C0112 respectively

•   new W0104 message on statement without effect

•   regexp support for dummy-variables (dummy-variables-rgx option replace dummy-variables) (implements #10027)

•   better global statement handling, see W0602, W0603, W0604 messages (implements #10344 and #10236)

•   --debug-mode option, disabling all checkers without error message and filtering others to only display error

•   fixed some R0201 (method could be a function) false positive

  What's New in Pylint 0.9.0?

Release date: 2006-01-10

•   a lot of updates to follow astng 0.14 API changes, so install logilab-astng 0.14 or greater before using this version of pylint

•   checker number 10 ! newstyle will search for problems regarding old style / new style classes usage problems (rely on astng 0.14 new style detection feature)

•   new 'load-plugins' options to load additional pylint plugins (usable from the command line or from a configuration file) (implements #10031)

•   check if a "pylintrc" file exists in the current working directory before using the one specified in the PYLINTRC environment variable or the default ~/.pylintrc or /etc/pylintrc

•   fixed W0706 (Identifier used to raise an exception is assigned...) false positive and reraising a caught exception instance

•   fixed E0611 (No name get in module blabla) false positive when accessing to a class'__dict__

•   fixed some E0203 ("access to member before its definition") false positive

•   fixed E0214 ("metaclass method first argument should be mcs) false positive with staticmethod used on a metaclass

•   fixed packaging which was missing the test/regrtest_data directory

•   W0212 (method could be a function) has been reclassified in the REFACTOR category as R0201, and is no more considerer when a method overrides an abstract method from an ancestor class

•   include module name in W0401 (wildcard import), as suggested by Amaury

•   when using the '--parseable', path are written relative to the current working directory if in a sub-directory of it (#9789)

•   'pylint --version' shows logilab-astng and logilab-common versions

•   fixed pylint.el to handle space in file names

•   misc lint style fixes

  What's New in Pylint 0.8.1?

Release date: 2005-11-07

•   fix "deprecated module" false positive when the code imports a module whose name starts with a deprecated module's name (close #10061)

•   fix "module has no name __dict__" false positive (Closes #10039)

•   fix "access to undefined variable __path__" false positive (close #10065)

•   fix "explicit return in __init__" false positive when return is actually in an inner function (Closes #10075)

  What's New in Pylint 0.8.0?

Release date: 2005-10-21

•   check names imported from a module exists in the module (E0611), patch contributed by Amaury Forgeot d'Arc

•   print a warning (W0212) for methods that could be a function (implements #9100)

•   new --defining-attr-methods option on classes checker

•   new --acquired-members option on the classes checker, used when --zope=yes to avoid false positive on acquired attributes (listed using this new option) (Closes #8616)

•   generate one E0602 for each use of an undefined variable (previously, only one for the first use but not for the following) (implements #1000)

•   make profile option saveable

•   fix Windows .bat file, patch contributed by Amaury Forgeot d'Arc

•   fix one more false positive for E0601 (access before definition) with for loop such as "for i in range(10): print i" (test func_noerror_defined_and_used_on_same_line)

•   fix false positive for E0201 (undefined member) when accessing to __name__ on a class object

•   fix astng checkers traversal order

•   fix bug in format checker when parsing a file from a platform using different new line characters (Closes #9239)

•   fix encoding detection regexp

•   fix --rcfile handling (support for --rcfile=file, Closes #9590)

  What's New in Pylint 0.7.0?

Release date: 2005-05-27

•   WARNING: pylint is no longer a logilab subpackage. Users may have to manually remove the old logilab/pylint directory.

•   introduce a new --additional-builtins option to handle user defined builtins

•   --reports option has now -r as short alias, and -i for --include-ids

•   fix a bug in the variables checker which may causing some false positives when variables are defined and used within the same statement (test func_noerror_defined_and_used_on_same_line)

•   this time, real fix of the "disable-msg in the config file" problem, test added to unittest_lint

•   fix bug with --list-messages and python -OO

•   fix possible false positive for W0201

  What's New in Pylint 0.6.4?

Release date: 2005-04-14

•   allow to parse files without extension when a path is given on the command line (test noext)

•   don't fail if we are unable to read an inline option (e.g. inside a module), just produce an information message (test func_i0010)

•   new message E0103 for break or continue outside loop (Closes #8883, test func_continue_not_in_loop)

•   fix bug in the variables checker, causing non detection of some actual name error (Closes #8884, test func_nameerror_on_string_substitution)

•   fix bug in the classes checker which was making pylint crash if "object" is assigned in a class inheriting from it (test func_noerror_object_as_class_attribute)

•   fix problem with the similar checker when related options are defined in a configuration file

•   new --generate-man option to generate pylint's man page (require the latest logilab.common (>= 0.9.3)

•   packaged (generated...) man page

  What's New in Pylint 0.6.3?

Release date: 2005-02-24

•   fix scope problem which may cause false positive and true negative on E0602

•   fix problem with some options such as disable-msg causing error when they are coming from the configuration file

  What's New in Pylint 0.6.2?

Release date: 2005-02-16

•   fix false positive on E0201 ("access to undefined member") with metaclasses

•   fix false positive on E0203 ("access to member before its definition") when attributes are defined in a parent class

•   fix false positive on W0706 ("identifier used to raise an exception assigned to...")

•   fix interpretation of "t" as value for the indent-string configuration variable

•   fix --rcfile so that --rcfile=pylintrc (only --rcfile pylintrc was working in earlier release)

•   new raw checker example in the examples/ directory

  What's New in Pylint 0.6.1?

Release date: 2005-02-04

•   new --rcfile option to specify the configuration file without the PYLINTRC environment variable

•   added an example module for a custom pylint checker (see the example/ directory)

•   some fixes to handle fixes in common 0.9.1 (should however still working with common 0.9.0, even if upgrade is recommended)

  What's New in Pylint 0.6.0?

Release date: 2005-01-20

•   refix pylint Emacs mode

•   no more traceback when just typing "pylint"

•   fix a bug which may cause crashes on resolving parent classes

•   fix problems with the format checker: don't chock on files containing multiple CR, avoid C0322, C0323, C0324 false positives with triple quoted string with quote inside

•   correctly detect access to member defined latter in __init__ method

•   now depends on common 0.8.1 to fix problem with interface resolution (Closes #8606)

•   new --list-msgs option describing available checkers and their messages

•   added windows specific documentation to the README file, contributed by Brian van den Broek

•   updated doc/features.txt (actually this file is now generated using the --list-msgs option), more entries into the FAQ

•   improved tests coverage

  What's New in Pylint 0.5.0?

Release date: 2004-10-19

•   avoid importing analyzed modules !

•   new Refactor and Convention message categories. Some Warnings have been remaped into those new categories

•   added "similar", a tool to find copied and pasted lines of code, both using a specific command line tool and integrated as a pylint's checker

•   imports checker may report import dependencies as a dot graph

•   new checker regrouping most Refactor detection (with some new metrics)

•   more command line options storable in the configuration file

•   fix bug with total / undocumented number of methods

  What's New in Pylint 0.4.2?

Release date: 2004-07-08

•   fix pylint Emacs mode

•   fix classes checkers to handler twisted interfaces

  What's New in Pylint 0.4.1?

Release date: 2004-05-14

•   fix the setup.py script to allow bdist_winst (well, the generated installer has not been tested...) with the necessary logilab/__init__.py file

•   fix file naming convention as suggested by Andreas Amoroso

•   fix stupid crash bug with bad method names

  What's New in Pylint 0.4.0?

Release date: 2004-05-10

•   fix file path with --parsable

•   --parsable option has been renamed to --parseable

•   added patch from Andreas Amoroso to output message to files instead of standard output

•   added Run to the list of correct variable names

•   fix variable names regexp and checking of local classes names

•   some basic handling of metaclasses

•   no-docstring-rgx apply now on classes too

•   new option to specify a different regexp for methods than for functions

•   do not display the evaluation report when no statements has been analysed

•   fixed crash with a class nested in a method

•   fixed format checker to deals with triple quoted string and lines with code and comment mixed

•   use logilab.common.ureports to layout reports

  What's New in Pylint 0.3.3?

Release date: 2004-02-17

•   added a parsable text output, used when the --parsable option is provided

•   added an Emacs mode using this output, available in the distrib's elisp directory

•   fixed some typos in messages

•   change include-ids options to yn, and allow it to be in the configuration file

•   do not chock on corrupted stats files

•   fixed bug in the format checker which may stop pylint execution

•   provide scripts for unix and windows to wrap the minimal pylint tk gui

  What's New in Pylint 0.3.2?

Release date: 2003-12-23

•   html-escape messages in the HTML reporter (bug reported by Juergen Hermann)

•   added "TODO" to the list of default note tags

•   added "rexec" to the list of default deprecated modules

•   fixed typos in some messages

  What's New in Pylint 0.3.1?

Release date: 2003-12-05

•   bug fix in format and classes checkers

•   remove print statement from imports checkers

•   provide a simple tk gui, essentially useful for windows users

  What's New in Pylint 0.3.0?

Release date: 2003-11-20

•   new exceptions checker, checking for string exception and empty except clauses.

•   imports checker checks for reimport of modules

•   classes checker checks for calls to ancestor's __init__ and abstract method not overridden. It doesn't complain anymore for unused import in __init__ files, and provides a new option ignore-interface-methods, useful when you're using zope Interface implementation in your project

•   base checker checks for disallowed builtins call (controlled by the bad-functions option) and for use of * and **

•   format checker checks for use of <> and "l" as long int marker

•   major internal API changes

•   use the rewrite of astng, based on compiler.ast

•   added unique id for messages, as suggested by Wolfgang Grafen

•   added unique id for reports

•   can take multiple modules or files as argument

•   new options command line options : --disable-msg, --enable-msg, --help-msg, --include-ids, --reports, --disable-report, --cache-size

•   --version shows the version of the python interpreter

•   removed some options which are now replaced by [en|dis]able-msg, or disable-report

•   read disable-msg and enable-msg options in source files (should be in comments on the top of the file, in the form "# pylint: disable-msg=W0402"

•   new message for modules importing themselves instead of the "cyclic import" message

•   fix bug with relative and cyclic imports

•   fix bug in imports checker (cycle was not always detected)

•   still fixes in format checker : don't check comment and docstring, check first line after an indent

•   allowed/prohibited names now apply to all identifiers, not only variables, so changed the configuration option from (good|bad)-variable-names to (good|bad)-names

•   added string, rexec and Bastion to the default list of deprecated modules

•   do not print redefinition warning for function/class/method defined in mutually exclusive branches

  What's New in Pylint 0.2.1?

Release date: 2003-10-10

•   added some documentation, fixed some typos

•   set environment variable PYLINT_IMPORT to 1 during pylint execution.

•   check that variables "imported" using the global statement exist

•   indentation problems are now warning instead of errors

•   fix checkers.initialize to try to load all files with a known python extension (patch from wrobell)

•   fix a bunch of messages

•   fix sample configuration file

•   fix the bad-construction option

•   fix encoding checker

•   fix format checker

  What's New in Pylint 0.2.0?

Release date: 2003-09-12

•   new source encoding / FIXME checker (pep 263)

•   new --zope option which trigger Zope import. Useful to check Zope products code.

•   new --comment option which enable the evaluation note comment (disabled by default).

•   a ton of bug fixes

•   easy functional test infrastructure

  What's New in Pylint 0.1.2?

Release date: 2003-06-18

•   bug fix release

•   remove dependency to pyreverse

  What's New in Pylint 0.1.1?

Release date: 2003-06-01

•   much more functionalities !

  What's New in Pylint 0.1?

Release date: 2003-05-19

•   initial release

  Frequently Asked Questions

  How do I install Pylint?

For command line use, pylint is installed with:

pip install pylint

Or if you want to also check spelling with enchant (you might need to install the enchant C library):

pip install pylint[spelling]

It can also be integrated in most editors or IDEs. More information can be found in the documentation.

  How do I contribute to Pylint?

We welcome all forms of contributions such as updates for documentation, new code, checking issues for duplicates or telling us that we can close them, confirming that issues still exist, creating issues because you found a bug or want a feature, etc. Everything is much appreciated!

Please follow the code of conduct and check the Contributor Guides if you want to make a code contribution.

  Does Pylint follow a versioning scheme?

See upgrading pylint in the installation guide.

  How do I find the name corresponding to a specific command line option?

See the configuration documentation.

  What is the format of the configuration file?

The configuration file can be an ini or toml file. See the exhaustive list of possible options.

  How to disable a particular message?

Read Messages control for details and examples.

  Pylint gave my code a negative rating out of ten. That can't be right!

Prior to Pylint 2.13.0, the score formula used by default had no lower bound. The new default score formula is

max(0, 0 if fatal else 10.0 - ((float(5 * error + warning + refactor + convention) / statement) * 10))

If your project contains a configuration file created by an earlier version of Pylint, you can set evaluation to the above expression to get the new behavior. Likewise, since negative values are still technically supported, evaluation can be set to a version of the above expression that does not enforce a floor of zero.

  How do I avoid getting unused argument warnings for API I do not control?

Prefix (ui) the callback's name by cb_ (callback), as in cb_onclick(...). By doing so arguments usage won't be checked. Another solution is to use one of the names defined in the "dummy-variables" configuration variable for unused argument ("_" and "dummy" by default).

  Why are there a bunch of messages disabled by default?

Either because they are prone to false positives or that they are opinionated enough to not be included as default messages.

You can see the plugin you need to explicitly load in the technical reference.

  Which messages should I disable to avoid duplicates if I use other popular linters ?

pycodestyle: bad-indentation, bare-except, line-too-long, missing-final-newline, multiple-statements, singleton-comparison, trailing-whitespace, unnecessary-semicolon, unneeded-not, wrong-import-position

pyflakes: undefined-variable, unused-import, unused-variable

mccabe: too-many-branches

pydocstyle: missing-module-docstring, missing-class-docstring, missing-function-docstring

pep8-naming: invalid-name, bad-classmethod-argument, bad-mcs-classmethod-argument, no-self-argument

isort and flake8-import-order: wrong-import-order

  How do I avoid "access to undefined member" messages in my mixin classes?

You should add the no-member message to your ignored-checks-for-mixins option and name your mixin class with a name which ends with "Mixin" or "mixin" (default) or change the default value by changing the mixin-class-rgx option.

  Where is the persistent data stored to compare between successive runs?

Analysis data are stored as a pickle file in a directory which is localized using the following rules:

•   value of the PYLINTHOME environment variable if set

•

"pylint" subdirectory of the user's XDG_CACHE_HOME if the environment variable is set, otherwise

•   Linux: "~/.cache/pylint"

•   macOS: "~/Library/Caches/pylint"

•   Windows: "C:Users<username>AppDataLocalpylint"

•   ".pylint.d" directory in the current directory

  Contact

  Bug reports, feedback

You think you have found a bug in Pylint? Well, this may be the case since Pylint and Python are under heavy development!

Please take the time to check if it is already in the issue tracker at https://github.com/PyCQA/pylint

Note that the issue might also be reported in one of Pylint's major dependencies, astroid:

•   https://github.com/PyCQA/astroid

  Discord server

You can discuss your problem using the discord server:

https://discord.com/invite/Egy6P8AMB5

  Mailing lists

The code-quality mailing list is shared with other tools that aim at improving the quality of python code.

You can subscribe to this mailing list at https://mail.python.org/mailman3/lists/code-quality.python.org/

Archives are available at https://mail.python.org/pipermail/code-quality/

Archives before April 2013 are not available anymore. At https://mail.python.org/pipermail/ it was under python-projects.

  Support
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AUTHOR
Logilab, PyCQA and contributors

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2003-2023, Logilab, PyCQA and contributors