####################
 Nuitka User Manual
####################

**********
 Overview
**********

This document is the recommended first read if you are interested in
using Nuitka, understand its use cases, check what you can expect,
license, requirements, credits, etc.

Nuitka is **the** Python compiler. It is written in Python. It is a
seamless replacement or extension to the Python interpreter and compiles
**every** construct that CPython 2.6, 2.7, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8,
3.9, 3.10, 3.11 have, when itself run with that Python version.

It then executes uncompiled code and compiled code together in an
extremely compatible manner.

You can use all Python library modules and all extension modules freely.

Nuitka translates the Python modules into a C level program that then
uses ``libpython`` and static C files of its own to execute in the same
way as CPython does.

All optimization is aimed at avoiding overhead, where it's unnecessary.
None is aimed at removing compatibility, although slight improvements
will occasionally be done, where not every bug of standard Python is
emulated, e.g. more complete error messages are given, but there is a
full compatibility mode to disable even that.

*******
 Usage
*******

Requirements
============

-  C Compiler: You need a compiler with support for C11 or alternatively
   for C++03 [#]_

   Currently this means, you need to use one of these compilers:

   -  The MinGW64 C11 compiler on Windows, must be based on gcc 11.2 or
      higher. It will be *automatically* downloaded if no usable C
      compiler is found, which is the recommended way of installing it,
      as Nuitka will also upgrade it for you.

   -  Visual Studio 2022 or higher on Windows [#]_, older versions will
      work but only supported for commercial users. Configure to use the
      English language pack for best results (Nuitka filters away
      garbage outputs, but only for English language). It will be used
      by default if installed.

   -  On all other platforms, the ``gcc`` compiler of at least version
      5.1, and below that the ``g++`` compiler of at least version 4.4
      as an alternative.

   -  The ``clang`` compiler on macOS X and most FreeBSD architectures.

   -  On Windows the ``clang-cl`` compiler on Windows can be used if
      provided by the Visual Studio installer.

-  Python: Version 2.6, 2.7 or 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 3.10,
   3.11

   .. important::

      For Python 3.3/3.4 and *only* those, we need other Python version
      as a *compile time* dependency.

      Nuitka itself is fully compatible with all listed versions, but
      Scons as an internally used tool is not.

      For these versions, you *need* a Python2 or Python 3.5 or higher
      installed as well, but only during the compile time only. That is
      for use with Scons (which orchestrates the C compilation), which
      does not support the same Python versions as Nuitka.

      In addition, on Windows, Python2 cannot be used because
      ``clcache`` does not work with it, there a Python 3.5 or higher
      needs to be installed.

      Nuitka finds these needed Python versions (e.g. on Windows via
      registry) and you shouldn't notice it as long as they are
      installed.

      Increasingly, other functionality is available when another Python
      has a certain package installed. For example, onefile compression
      will work for a Python 2.x when another Python is found that has
      the ``zstandard`` package installed.

   .. admonition:: Moving binaries to other machines

      The created binaries can be made executable independent of the
      Python installation, with ``--standalone`` and ``--onefile``
      options.

   .. admonition:: Binary filename suffix

      The created binaries have an ``.exe`` suffix on Windows. On other
      platforms they have no suffix for standalone mode, or ``.bin``
      suffix, that you are free to remove or change, or specify with the
      ``-o`` option.

      The suffix for acceleration mode is added just to be sure that the
      original script name and the binary name do not ever collide, so
      we can safely do an overwrite without destroying the original
      source file.

   .. admonition:: It **has to** be CPython, Anaconda Python.

      You need the standard Python implementation, called "CPython", to
      execute Nuitka, because it is closely tied to implementation
      details of it.

   .. admonition:: It **cannot be** from Windows app store

      It is known that Windows app store Python definitely does not
      work, it's checked against. And on macOS "pyenv" likely does
      **not** work.

-  Operating System: Linux, FreeBSD, NetBSD, macOS X, and Windows
   (32bits/64 bits/ARM).

   Others may work as well. The portability is expected to be generally
   good, but the e.g. Scons usage may have to be adapted. Make sure to
   match Windows Python and C compiler architecture, or else you will
   get cryptic error messages.

-  Architectures: x86, x86_64 (amd64), and arm, likely many more

   Other architectures are expected to also work, out of the box, as
   Nuitka is generally not using any hardware specifics. These are just
   the ones tested and known to be good. Feedback is welcome. Generally,
   the architectures that Debian supports can be considered good and
   tested too.

.. [#]

   Support for this C11 is a given with gcc 5.x or higher or any clang
   version.

   The MSVC compiler doesn't do it yet. But as a workaround, as the C++03
   language standard is very overlapping with C11, it is then used instead
   where the C compiler is too old. Nuitka used to require a C++ compiler
   in the past, but it changed.

.. [#]

   Download for free from
   https://www.visualstudio.com/en-us/downloads/download-visual-studio-vs.aspx
   (the community editions work just fine).

   The latest version is recommended but not required. On the other hand,
   there is no need to except to support pre-Windows 10 versions, and they
   might work for you, but support of these configurations is only
   available to commercial users.

Command Line
============

The recommended way of executing Nuitka is ``<the_right_python> -m
nuitka`` to be absolutely certain which Python interpreter you are
using, so it is easier to match with what Nuitka has.

The next best way of executing Nuitka bare that is from a source
checkout or archive, with no environment variable changes, most
noteworthy, you do not have to mess with ``PYTHONPATH`` at all for
Nuitka. You just execute the ``nuitka`` and ``nuitka-run`` scripts
directly without any changes to the environment. You may want to add the
``bin`` directory to your ``PATH`` for your convenience, but that step
is optional.

Moreover, if you want to execute with the right interpreter, in that
case, be sure to execute ``<the_right_python> bin/nuitka`` and be good.

.. admonition:: Pick the right Interpreter

   If you encounter a ``SyntaxError`` you absolutely most certainly have
   picked the wrong interpreter for the program you are compiling.

Nuitka has a ``--help`` option to output what it can do:

.. code:: bash

   nuitka --help

The ``nuitka-run`` command is the same as ``nuitka``, but with a
different default. It tries to compile *and* directly execute a Python
script:

.. code:: bash

   nuitka-run --help

This option that is different is ``--run``, and passing on arguments
after the first non-option to the created binary, so it is somewhat more
similar to what plain ``python`` will do.

Installation
============

For most systems, there will be packages on the `download page
<https://nuitka.net/doc/download.html>`__ of Nuitka. But you can also
install it from source code as described above, but also like any other
Python program it can be installed via the normal ``python setup.py
install`` routine.

License
=======

Nuitka is licensed under the Apache License, Version 2.0; you may not
use it except in compliance with the License.

You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.

*************************************
 Tutorial Setup and build on Windows
*************************************

This is basic steps if you have nothing installed, of course if you have
any of the parts, just skip it.

Setup
=====

Install Python
--------------

-  Download and install Python from
   https://www.python.org/downloads/windows

-  Select one of ``Windows x86-64 web-based installer`` (64 bits Python,
   recommended) or ``x86 executable`` (32 bits Python) installer.

-  Verify it's working using command ``python --version``.

Install Nuitka
--------------

-  ``python -m pip install nuitka``

-  Verify using command ``python -m nuitka --version``

Write some code and test
========================

Create a folder for the Python code
-----------------------------------

-  ``mkdir`` HelloWorld

-  make a python file named **hello.py**

.. code:: python

   def talk(message):
       return "Talk " + message


   def main():
       print(talk("Hello World"))


   if __name__ == "__main__":
       main()

Test your program
-----------------

Do as you normally would. Running Nuitka on code that works incorrectly
is not easier to debug.

.. code:: bash

   python hello.py

----

Build it using
--------------

.. code:: bash

   python -m nuitka hello.py

.. note::

   This will prompt you to download a C caching tool (to speed up
   repeated compilation of generated C code) and a MinGW64 based C
   compiler unless you have a suitable MSVC installed. Say ``yes`` to
   both those questions.

Run it
------

Execute the ``hello.exe`` created near ``hello.py``.

Distribute
----------

To distribute, build with ``--standalone`` option, which will not output
a single executable, but a whole folder. Copy the resulting
``hello.dist`` folder to the other machine and run it.

You may also try ``--onefile`` which does create a single file, but make
sure that the mere standalone is working, before turning to it, as it
will make the debugging only harder, e.g. in case of missing data files.

***********
 Use Cases
***********

Use Case 1 - Program compilation with all modules embedded
==========================================================

If you want to compile a whole program recursively, and not only the
single file that is the main program, do it like this:

.. code:: bash

   python -m nuitka --follow-imports program.py

.. note::

   There are more fine grained controls than ``--follow-imports``
   available. Consider the output of ``nuitka --help``. Including less
   modules into the compilation, but instead using normal Python for it
   will make it faster to compile.

In case you have a source directory with dynamically loaded files, i.e.
one which cannot be found by recursing after normal import statements
via the ``PYTHONPATH`` (which would be the recommended way), you can
always require that a given directory shall also be included in the
executable:

.. code:: bash

   python -m nuitka --follow-imports --include-plugin-directory=plugin_dir program.py

.. note::

   If you don't do any dynamic imports, simply setting your
   ``PYTHONPATH`` at compilation time is what you should do.

   Use ``--include-plugin-directory`` only if you make ``__import__()``
   calls that Nuitka cannot predict, because they e.g. depend on command
   line parameters. Nuitka also warns about these, and point to the
   option.

.. note::

   The resulting filename will be ``program.exe`` on Windows,
   ``program.bin`` on other platforms.

.. note::

   The resulting binary still depend on CPython and used C extension
   modules being installed.

   If you want to be able to copy it to another machine, use
   ``--standalone`` and copy the created ``program.dist`` directory and
   execute the ``program.exe`` (Windows) or ``program`` (other
   platforms) put inside.

Use Case 2 - Extension Module compilation
=========================================

If you want to compile a single extension module, all you have to do is
this:

.. code:: bash

   python -m nuitka --module some_module.py

The resulting file ``some_module.so`` can then be used instead of
``some_module.py``.

.. note::

   It's left as an exercise to the reader, to find out what happens if
   both are present.

.. note::

   The option ``--follow-import-to`` and work as well, but the included
   modules will only become importable *after* you imported the
   ``some_module`` name. If these kinds of imports are invisible to
   Nuitka, e.g. dynamically created, you can use ``--include-module`` or
   ``--include-package`` in that case, but for static imports it should
   not be needed.

.. note::

   An extension module can never include other extension modules. You
   will have to create a wheel for this to be doable.

.. note::

   The resulting extension module can only be loaded into a CPython of
   the same version and doesn't include other extension modules.

Use Case 3 - Package compilation
================================

If you need to compile a whole package and embed all modules, that is
also feasible, use Nuitka like this:

.. code:: bash

   python -m nuitka --module some_package --include-package=some_package

.. note::

   The inclusion of the package contents needs to be provided manually,
   otherwise, the package is mostly empty. You can be more specific if
   you want, and only include part of it, or exclude part of it, e.g.
   with ``--nofollow-import-to='*.tests'`` you would not include the
   unused test part of your code.

.. note::

   Data files located inside the package will not be embedded by this
   process, you need to copy them yourself with this approach.
   Alternatively you can use the `file embedding of Nuitka commercial
   <https://nuitka.net/doc/commercial/protect-data-files.html>`__.

Use Case 4 - Program Distribution
=================================

For distribution to other systems, there is the standalone mode which
produces a folder for which you can specify ``--standalone``.

.. code:: bash

   python -m nuitka --standalone program.py

Following all imports is default in this mode. You can selectively
exclude modules by specifically saying ``--nofollow-import-to``, but
then an ``ImportError`` will be raised when import of it is attempted at
program run time. This may cause different behavior, but it may also
improve your compile time if done wisely.

For data files to be included, use the option
``--include-data-files=<source>=<target>`` where the source is a file
system path, but target has to be specified relative. For standalone you
can also copy them manually, but this can do extra checks, and for
onefile mode, there is no manual copying possible.

To copy some or all file in a directory, use the option
``--include-data-files=/etc/*.txt=etc/`` where you get to specify shell
patterns for the files, and a subdirectory where to put them, indicated
by the trailing slash.

To copy a whole folder with all files, you can use
``--include-data-dir=/path/to/images=images`` which will copy all files
including a potential subdirectory structure. You cannot filter here,
i.e. if you want only a partial copy, remove the files beforehand.

For package data, there is a better way, using
``--include-package-data`` which detects data files of packages
automatically and copies them over. It even accepts patterns in shell
style. It spares you the need to find the package directory yourself and
should be preferred whenever available.

With data files, you are largely on your own. Nuitka keeps track of ones
that are needed by popular packages, but it might be incomplete. Raise
issues if you encounter something in these.

When that is working, you can use the onefile mode if you so desire.

.. code:: bash

   python -m nuitka --onefile program.py

This will create a single binary, that extracts itself on the target,
before running the program. But notice, that accessing files relative to
your program is impacted, make sure to read the section `Onefile:
Finding files`_ as well.

.. code:: bash

   # Create a binary that unpacks into a temporary folder
   python -m nuitka --onefile program.py

.. note::

   There are more platform specific options, e.g. related to icons,
   splash screen, and version information, consider the ``--help``
   output for the details of these and check the section `Tweaks_`.

For the unpacking, by default a unique user temporary path one is used,
and then deleted, however this default
``--onefile-tempdir-spec="%TEMP%/onefile_%PID%_%TIME%"`` can be
overridden with a path specification that is using then using a cached
path, avoiding repeated unpacking, e.g. with
``--onefile-tempdir-spec="%CACHE_DIR%/%COMPANY%/%PRODUCT%/%VERSION"``
which uses version information, and user specific cache directory.

.. note::

   Using cached paths will e.g. be relevant too, when Windows Firewall
   comes into play, because otherwise, the binary will be a different
   one to it each time it is run.

Currently these expanded tokens are available:

+-------------+-----------------------------------------------------------+----------------------------------+
| Token       | What this Expands to                                      | Example                          |
+=============+===========================================================+==================================+
| %TEMP%      | User temporary file directory                             | C:\Users\...\AppData\Locals\Temp |
+-------------+-----------------------------------------------------------+----------------------------------+
| %PID%       | Process ID                                                | 2772                             |
+-------------+-----------------------------------------------------------+----------------------------------+
| %TIME%      | Time in seconds since the epoch.                          | 1299852985                       |
+-------------+-----------------------------------------------------------+----------------------------------+
| %PROGRAM%   | Full program run-time filename of executable.             | C:\SomeWhere\YourOnefile.exe     |
+-------------+-----------------------------------------------------------+----------------------------------+
| %CACHE_DIR% | Cache directory for the user.                             | C:\Users\SomeBody\AppData\Local  |
+-------------+-----------------------------------------------------------+----------------------------------+
| %COMPANY%   | Value given as ``--company-name``                         | YourCompanyName                  |
+-------------+-----------------------------------------------------------+----------------------------------+
| %PRODUCT%   | Value given as ``--product-name``                         | YourProductName                  |
+-------------+-----------------------------------------------------------+----------------------------------+
| %VERSION%   | Combination of ``--file-version`` & ``--product-version`` | 3.0.0.0-1.0.0.0                  |
+-------------+-----------------------------------------------------------+----------------------------------+
| %HOME%      | Home directory for the user.                              | /home/somebody                   |
+-------------+-----------------------------------------------------------+----------------------------------+

.. note::

   It is your responsibility to make the path provided unique, on
   Windows a running program will be locked, and while using a fixed
   folder name is possible, it can cause locking issues in that case,
   where the program gets restarted.

   Usually you need to use ``%TIME%`` or at least ``%PID%`` to make a
   path unique, and this is mainly intended for use cases, where e.g.
   you want things to reside in a place you choose or abide your naming
   conventions.

Use Case 5 - Setuptools Wheels
==============================

If you have a ``setup.py``, ``setup.cfg`` or ``pyproject.toml`` driven
creation of wheels for your software in place, putting Nuitka to use is
extremely easy.

Lets start with the most common ``setuptools`` approach, you can -
having Nuitka installed of course, simply execute the target
``bdist_nuitka`` rather than the ``bdist_wheel``. It takes all the
options and allows you to specify some more, that are specific to
Nuitka.

.. code:: python

   # For setup.py if not you't use other build systems:
   setup(
      ...,
      command_options={
         'nuitka': {
            # boolean option, e.g. if you cared for C compilation commands
            '--show-scons': True,
            # options without value, e.g. enforce using Clang
            '--clang': None,
            # options with single values, e.g. enable a plugin of Nuitka
            '--enable-plugin': "pyside2",
            # options with several values, e.g. avoiding including modules
            '--nofollow-import-to' : ["*.tests", "*.distutils"],
         }
      },
   )

   # For setup.py with other build systems:
   # The tuple nature of the arguments is required by the dark nature of
   # "setuptools" and plugins to it, that insist on full compatibility,
   # e.g. "setuptools_rust"

   setup(
      ...,
      command_options={
         'nuitka': {
            # boolean option, e.g. if you cared for C compilation commands
            '--show-scons': ("setup.py", True),
            # options without value, e.g. enforce using Clang
            '--clang': ("setup.py", None),
            # options with single values, e.g. enable a plugin of Nuitka
            '--enable-plugin': ("setup.py", "pyside2"),
            # options with several values, e.g. avoiding including modules
            '--nofollow-import-to' : ("setup.py", ["*.tests", "*.distutils"]),
         }
      },
   )

If for some reason, you cannot or do not what to change the target, you
can add this to your ``setup.py``.

.. code:: python

   # For setup.py
   setup(
      ...,
      build_with_nuitka=True
   )

.. note::

   To temporarily disable the compilation, you could remove above line,
   or edit the value to ``False`` by or take its value from an
   environment variable if you so choose, e.g.
   ``bool(os.environ.get("USE_NUITKA", "True"))``. This is up to you.

Or you could put it in your ``setup.cfg``

.. code:: toml

   [metadata]
   build_with_nuitka = True

And last, but not least, Nuitka also supports the new ``build`` meta, so
when you have a ``pyproject.toml`` already, simple replace or add this
value:

.. code:: toml

   [build-system]
   requires = ["setuptools>=42", "wheel", "nuitka", "toml"]
   build-backend = "nuitka.distutils.Build"

   [nuitka]
   # These are not recommended, but they make it obvious to have effect.

   # boolean option, e.g. if you cared for C compilation commands, leading
   # dashes are omitted
   show-scons = true

   # options with single values, e.g. enable a plugin of Nuitka
   enable-plugin = pyside2

   # options with several values, e.g. avoiding including modules, accepts
   # list argument.
   nofollow-import-to = ["*.tests", "*.distutils"]

.. note::

   For the ``nuitka`` requirement above absolute paths like
   ``C:\Users\...\Nuitka`` will also work on Linux, use an absolute path
   with *two* leading slashes, e.g. ``//home/.../Nuitka``.

Use Case 6 - Multidist
======================

If you have multiple programs, that each should be executable, in the
past you had to compile multiple times, and deploy all of these. With
standalone mode, this of course meant that you were fairly wasteful, as
sharing the folders could be done, but wasn't really supported by
Nuitka.

Enter ``Multidist``. There is an option ``--main-path`` that replaces or
adds to the positional argument given. And it can be given multiple
times. When given multiple times, Nuitka will create a binary that
contains the code of all the programs given, but sharing modules used in
them. They therefore do not have to be distributed multiple times.

Lets call the basename of the main path, and entry point. The names of
these must of course be different. Then the created binary can execute
either entry point, and will react to what ``sys.argv[0]`` appears to
it. So if executed in the right way (with something like ``subprocess``
or OS API you can control this name), or by renaming or copying the
binary, or symlinking to it, you can then achieve the miracle.

This allows to combine very different programs into one.

.. note::

   This feature is still experimental. Use with care and report your
   findings should you encounter anything that is undesirable behavior

This mode works with standalone, onefile, and mere acceleration. It does
not work with module mode.

********
 Tweaks
********

Icons
=====

For good looks, you may specify icons. On Windows, you can provide an
icon file, a template executable, or a PNG file. All of these will work
and may even be combined:

.. code:: bash

   # These create binaries with icons on Windows
   python -m nuitka --onefile --windows-icon-from-ico=your-icon.png program.py
   python -m nuitka --onefile --windows-icon-from-ico=your-icon.ico program.py
   python -m nuitka --onefile --windows-icon-template-exe=your-icon.ico program.py

   # These create application bundles with icons on macOS
   python -m nuitka --macos-create-app-bundle --macos-app-icon=your-icon.png program.py
   python -m nuitka --macos-create-app-bundle --macos-app-icon=your-icon.icns program.py

.. note::

   With Nuitka, you do not have to create platform specific icons, but
   instead it will convert e.g. PNG, but also other format on the fly
   during the build.

MacOS Entitlements
==================

Entitlements for an macOS application bundle can be added with the
option, ``--macos-app-protected-resource``, all values are listed on
`this page from Apple
<https://developer.apple.com/documentation/bundleresources/information_property_list/protected_resources>`__

An example value would be
``--macos-app-protected-resource=NSMicrophoneUsageDescription:Microphone
access`` for requesting access to a Microphone. After the colon, the
descriptive text is to be given.

.. note::

   Beware that in the likely case of using spaces in the description
   part, you need to quote it for your shell to get through to Nuitka
   and not be interpreted as Nuitka arguments.

Console Window
==============

On Windows, the console is opened by programs unless you say so. Nuitka
defaults to this, effectively being only good for terminal programs, or
programs where the output is requested to be seen. There is a difference
in ``pythonw.exe`` and ``python.exe`` along those lines. This is
replicated in Nuitka with the option ``--disable-console``. Nuitka
recommends you to consider this in case you are using ``PySide6`` e.g.
and other GUI packages, e.g. ``wx``, but it leaves the decision up to
you. In case, you know your program is console application, just using
``--enable-console`` which will get rid of these kinds of outputs from
Nuitka.

.. note::

   The ``pythonw.exe`` is never good to be used with Nuitka, as you
   cannot see its output.

Splash screen
=============

Splash screens are useful when program startup is slow. Onefile startup
itself is not slow, but your program may be, and you cannot really know
how fast the computer used will be, so it might be a good idea to have
them. Luckily with Nuitka, they are easy to add for Windows.

For splash screen, you need to specify it as an PNG file, and then make
sure to disable the splash screen when your program is ready, e.g. has
complete the imports, prepared the window, connected to the database,
and wants the splash screen to go away. Here we are using the project
syntax to combine the code with the creation, compile this:

.. code:: python

   # nuitka-project: --onefile
   # nuitka-project: --onefile-windows-splash-screen-image={MAIN_DIRECTORY}/Splash-Screen.png

   # Whatever this is obviously
   print("Delaying startup by 10s...")
   import time
   time.sleep(10)

   # Use this code to signal the splash screen removal.
   if "NUITKA_ONEFILE_PARENT" in os.environ:
      splash_filename = os.path.join(
         tempfile.gettempdir(),
         "onefile_%d_splash_feedback.tmp" % int(os.environ["NUITKA_ONEFILE_PARENT"]),
      )

      if os.path.exists(splash_filename):
         os.unlink(splash_filename)

   print("Done... splash should be gone.")
   ...

   # Rest of your program goes here.

Reports
=======

For analysis of your program and Nuitka packaging, there is the
`Compilation Report`_ available. You can also make custom reports
providing your own template, with a few of them built-in to Nuitka.
These reports carry all the detail information, e.g. when a module was
attempted to be imported, but not found, you can see where that happens.
For bug reporting, it is very much recommended to provide the report.

******************
 Typical Problems
******************

Windows Virus scanners
======================

Binaries compiled on Windows with default settings of Nuitka and no
further actions taken might be recognized by some AV vendors as malware.
This is avoidable, but only in Nuitka commercial there is actual support
and instructions for how to do it, seeing this as a typical commercial
only need. https://nuitka.net/doc/commercial.html

Memory issues and compiler bugs
===============================

Sometimes the C compilers will crash saying they cannot allocate memory
or that some input was truncated, or similar error messages, clearly
from it. There are several options you can explore here:

Ask Nuitka to use less memory
-----------------------------

There is a dedicated option ``--low-memory`` which influences decisions
of Nuitka, such that it avoids high usage of memory during compilation
at the cost of increased compile time.

Avoid 32 bit C compiler/assembler memory limits
-----------------------------------------------

Do not use a 32 bits compiler, but a 64 bit one. If you are using Python
with 32 bits on Windows, you most definitely ought to use MSVC as the C
compiler, and not MinGW64. The MSVC is a cross compiler, and can use
more memory than gcc on that platform. If you are not on Windows, that
is not an option of course. Also using the 64 bits Python will work.

Use a minimal virtualenv
------------------------

When you compile from a living installation, that may well have many
optional dependencies of your software installed. Some software, will
then have imports on these, and Nuitka will compile them as well. Not
only may these be just the trouble makers, they also require more
memory, so get rid of that. Of course you do have to check that your
program has all needed dependencies before you attempt to compile, or
else the compiled program will equally not run.

Use LTO compilation or not
--------------------------

With ``--lto=yes`` or ``--lto=no`` you can switch the C compilation to
only produce bytecode, and not assembler code and machine code directly,
but make a whole program optimization at the end. This will change the
memory usage pretty dramatically, and if you error is coming from the
assembler, using LTO will most definitely avoid that.

Switch the C compiler to clang
------------------------------

People have reported that programs that fail to compile with gcc due to
its bugs or memory usage work fine with clang on Linux. On Windows, this
could still be an option, but it needs to be implemented first for the
automatic downloaded gcc, that would contain it. Since MSVC is known to
be more memory effective anyway, you should go there, and if you want to
use Clang, there is support for the one contained in MSVC.

Add a larger swap file to your embedded Linux
---------------------------------------------

On systems with not enough RAM, you need to use swap space. Running out
of it is possibly a cause, and adding more swap space, or one at all,
might solve the issue, but beware that it will make things extremely
slow when the compilers swap back and forth, so consider the next tip
first or on top of it.

Limit the amount of compilation jobs
------------------------------------

With the ``--jobs`` option of Nuitka, it will not start many C compiler
instances at once, each competing for the scarce resource of RAM. By
picking a value of one, only one C compiler instance will be running,
and on a 8 core system, that reduces the amount of memory by factor 8,
so that's a natural choice right there.

Dynamic ``sys.path``
====================

If your script modifies ``sys.path`` to e.g. insert directories with
source code relative to it, Nuitka will not be able to see those.
However, if you set the ``PYTHONPATH`` to the resulting value, it will
be able to compile it and find the used modules from these paths as
well.

Manual Python File Loading
--------------------------

A very frequent pattern with private code is that it scans plugin
directories of some kind, and e.g. uses ``os.listdir``, then considers
Python filenames, and then opens a file and does ``exec`` on them. This
approach is working for Python code, but for compiled code, you should
use this much cleaner approach, that works for pure Python code and is a
lot less vulnerable.

.. code:: python

   # Using a package name, to locate the plugins. This is also a sane
   # way to organize them into a directory.
   scan_path = scan_package.__path__

   for item in pkgutil.iter_modules(scan_path):
      importlib.import_module(scan_package.__name__ + "." + item.name)

      # You may want to do it recursively, but we don't do this here in
      # this example. If you want to, handle that in this kind of branch.
      if item.ispkg:
         ...

Missing data files in standalone
================================

If your program fails to file data, it can cause all kinds of different
behaviors, e.g. a package might complain it is not the right version,
because a ``VERSION`` file check defaulted to unknown. The absence of
icon files or help texts, may raise strange errors.

Often the error paths for files not being present are even buggy and
will reveal programming errors like unbound local variables. Please look
carefully at these exceptions keeping in mind that this can be the
cause. If you program works without standalone, chances are data files
might be cause.

The most common error indicating file absence is of course an uncaught
``FileNotFoundError`` with a filename. You should figure out what
package is missing files and then use ``--include-package-data``
(preferably), or ``--include-data-dir``/``--include-data-files`` to
include them.

Missing DLLs in standalone
==========================

Nuitka has plugins that deal with copying DLLs. For NumPy, SciPy,
Tkinter, etc.

These need special treatment to be able to run on other systems.
Manually copying them is not enough and will given strange errors.
Sometimes newer version of packages, esp. NumPy can be unsupported. In
this case you will have to raise an issue, and use the older one.

Dependency creep in standalone
==============================

Some packages are a single import, but to Nuitka mean that more than a
thousand packages (literally) are to be included. The prime example of
Pandas, which does want to plug and use just about everything you can
imagine. Multiple frameworks for syntax highlighting everything
imaginable take time.

Nuitka will have to learn effective caching to deal with this in the
future. Right now, you will have to deal with huge compilation times for
these.

A major weapon in fighting dependency creep should be applied, namely
the ``anti-bloat`` plugin, which offers interesting abilities, that can
be put to use and block unneeded imports, giving an error for where they
occur. Use it e.g. like this ``--noinclude-pytest-mode=nofollow
--noinclude-setuptools-mode=nofollow`` and e.g. also
``--noinclude-custom-mode=setuptools:error`` to get the compiler to
error out for a specific package. Make sure to check its help output. It
can take for each module of your choice, e.g. forcing also that e.g.
``PyQt5`` is considered uninstalled for standalone mode.

It's also driven by a configuration file, ``anti-bloat.yml`` that you
can contribute to, removing typical bloat from packages. Feel free to
enhance it and make PRs towards Nuitka with it.

Standalone: Finding files
=========================

The standard code that normally works, also works, you should refer to
``os.path.dirname(__file__)`` or use all the packages like ``pkgutil``,
``pkg_resources``, ``importlib.resources`` to locate data files near the
standalone binary.

.. important::

   What you should **not** do, is use the current directory
   ``os.getcwd``, or assume that this is the script directory, e.g. with
   paths like ``data/``.

   If you did that, it was never good code. Links, to a program,
   launching from another directory, etc. will all fail in bad ways. Do
   not make assumptions about the directory your program is started
   from.

Onefile: Finding files
======================

There is a difference between ``sys.argv[0]`` and ``__file__`` of the
main module for onefile more, that is caused by using a bootstrap to a
temporary location. The first one will be the original executable path,
where as the second one will be the temporary or permanent path the
bootstrap executable unpacks to. Data files will be in the later
location, your original environment files will be in the former
location.

Given 2 files, one which you expect to be near your executable, and one
which you expect to be inside the onefile binary, access them like this.

.. code:: python

   # This will find a file *near* your onefile.exe
   open(os.path.join(os.path.dirname(sys.argv[0]), "user-provided-file.txt"))
   # This will find a file *inside* your onefile.exe
   open(os.path.join(os.path.dirname(__file__), "user-provided-file.txt"))

Windows Programs without console give no errors
===============================================

For debugging purposes, remove ``--disable-console`` or use the options
``--windows-force-stdout-spec`` and ``--windows-force-stderr-spec`` with
paths as documented for ``--onefile-tempdir-spec`` above. These can be
relative to the program or absolute, so you can see the outputs given.

Deep copying uncompiled functions
=================================

Sometimes people use this kind of code, which for packages on PyPI, we
deal with by doing source code patches on the fly. If this is in your
own code, here is what you can do:

.. code:: python

   def binder(func, name):
      result = types.FunctionType(func.__code__, func.__globals__, name=func.__name__, argdefs=func.__defaults__, closure=func.__closure__)
      result = functools.update_wrapper(result, func)
      result.__kwdefaults__ = func.__kwdefaults__
      result.__name__ = name
      return result

Compiled functions cannot be used to create uncompiled ones from, so the
above code, will not work. However, there is a dedicated ``clone``
method, that is specific to them, so use this instead.

.. code:: python

   def binder(func, name):
      try:
         result = func.clone()
      except AttributeError:
         result = types.FunctionType(func.__code__, func.__globals__, name=func.__name__, argdefs=func.__defaults__, closure=func.__closure__)
         result = functools.update_wrapper(result, func)
         result.__kwdefaults__ = func.__kwdefaults__

      result.__name__ = name
      return result

******
 Tips
******

Nuitka Options in the code
==========================

There is support for conditional options, and options using pre-defined
variables, this is an example:

.. code:: python

   # Compilation mode, support OS specific.
   # nuitka-project-if: {OS} in ("Windows", "Linux", "Darwin", "FreeBSD"):
   #    nuitka-project: --onefile
   # nuitka-project-if: {OS} not in ("Windows", "Linux", "Darwin", "FreeBSD"):
   #    nuitka-project: --standalone

   # The PySide2 plugin covers qt-plugins
   # nuitka-project: --enable-plugin=pyside2
   # nuitka-project: --include-qt-plugins=sensible,qml

The comments must be a start of line, and indentation is to be used, to
end a conditional block, much like in Python. There are currently no
other keywords than the used ones demonstrated above.

You can put arbitrary Python expressions there, and if you wanted to
e.g. access a version information of a package, you could simply use
``__import__("module_name").__version__`` if that would be required to
e.g. enable or disable certain Nuitka settings. The only thing Nuitka
does that makes this not Python expressions, is expanding ``{variable}``
for a pre-defined set of variables:

Table with supported variables:

+------------------+--------------------------------+------------------------------------------+
| Variable         | What this Expands to           | Example                                  |
+==================+================================+==========================================+
| {OS}             | Name of the OS used            | Linux, Windows, Darwin, FreeBSD, OpenBSD |
+------------------+--------------------------------+------------------------------------------+
| {Version}        | Version of Nuitka              | e.g. (0, 6, 16)                          |
+------------------+--------------------------------+------------------------------------------+
| {Commercial}     | Version of Nuitka Commercial   | e.g. (0, 9, 4)                           |
+------------------+--------------------------------+------------------------------------------+
| {Arch}           | Architecture used              | x86_64, arm64, etc.                      |
+------------------+--------------------------------+------------------------------------------+
| {MAIN_DIRECTORY} | Directory of the compiled file | some_dir/maybe_relative                  |
+------------------+--------------------------------+------------------------------------------+
| {Flavor}         | Variant of Python              | e.g. Debian Python, Anaconda Python      |
+------------------+--------------------------------+------------------------------------------+

The use of ``{MAIN_DIRECTORY}`` is recommended when you want to specify
a filename relative to the main script, e.g. for use in data file
options or user package configuration yaml files,

.. code:: python

   # nuitka-project: --include-data-files={MAIN_DIRECTORY}/my_icon.png=my_icon.png
   # nuitka-project: --user-package-configuration-file={MAIN_DIRECTORY}/user.nuitka-package.config.yml

Python command line flags
=========================

For passing things like ``-O`` or ``-S`` to Python, to your compiled
program, there is a command line option name ``--python-flag=`` which
makes Nuitka emulate these options.

The most important ones are supported, more can certainly be added.

Caching compilation results
===========================

The C compiler, when invoked with the same input files, will take a long
time and much CPU to compile over and over. Make sure you are having
``ccache`` installed and configured when using gcc (even on Windows). It
will make repeated compilations much faster, even if things are not yet
not perfect, i.e. changes to the program can cause many C files to
change, requiring a new compilation instead of using the cached result.

On Windows, with gcc Nuitka supports using ``ccache.exe`` which it will
offer to download from an official source and it automatically. This is
the recommended way of using it on Windows, as other versions can e.g.
hang.

Nuitka will pick up ``ccache`` if it's in found in system ``PATH``, and
it will also be possible to provide if by setting
``NUITKA_CCACHE_BINARY`` to the full path of the binary, this is for use
in CI systems where things might be non-standard.

For the MSVC compilers and ClangCL setups, using the ``clcache`` is
automatic and included in Nuitka.

Control where Caches live
=========================

The storage for cache results of all kinds, downloads, cached
compilation results from C and Nuitka, is done in a platform dependent
directory as determined by the ``appdirs`` package. However, you can
override it with setting the environment variable ``NUITKA_CACHE_DIR``
to a base directory. This is for use in environments where the home
directory is not persisted, but other paths are.

Runners
=======

Avoid running the ``nuitka`` binary, doing ``python -m nuitka`` will
make a 100% sure you are using what you think you are. Using the wrong
Python will make it give you ``SyntaxError`` for good code or
``ImportError`` for installed modules. That is happening, when you run
Nuitka with Python2 on Python3 code and vice versa. By explicitly
calling the same Python interpreter binary, you avoid that issue
entirely.

Fastest C Compilers
===================

The fastest binaries of ``pystone.exe`` on Windows with 64 bits Python
proved to be significantly faster with MinGW64, roughly 20% better
score. So it is recommended for use over MSVC. Using ``clang-cl.exe`` of
Clang7 was faster than MSVC, but still significantly slower than
MinGW64, and it will be harder to use, so it is not recommended.

On Linux for ``pystone.bin`` the binary produced by ``clang6`` was
faster than ``gcc-6.3``, but not by a significant margin. Since gcc is
more often already installed, that is recommended to use for now.

Differences in C compilation times have not yet been examined.

Unexpected Slowdowns
====================

Using the Python DLL, like standard CPython does can lead to unexpected
slowdowns, e.g. in uncompiled code that works with Unicode strings. This
is because calling to the DLL rather than residing in the DLL causes
overhead, and this even happens to the DLL with itself, being slower,
than a Python all contained in one binary.

So if feasible, aim at static linking, which is currently only possible
with Anaconda Python on non-Windows, Debian Python2, self compiled
Pythons (do not activate ``--enable-shared``, not needed), and installs
created with ``pyenv``.

.. note::

   On Anaconda, you may need to execute ``conda install
   libpython-static``

Standalone executables and dependencies
=======================================

The process of making standalone executables for Windows traditionally
involves using an external dependency walker in order to copy necessary
libraries along with the compiled executables to the distribution
folder.

There is plenty of ways to find that something is missing. Do not
manually copy things into the folder, esp. not DLLs, as that's not going
to work. Instead make bug reports to get these handled by Nuitka
properly.

Windows errors with resources
=============================

On Windows, the Windows Defender tool and the Windows Indexing Service
both scan the freshly created binaries, while Nuitka wants to work with
it, e.g. adding more resources, and then preventing operations randomly
due to holding locks. Make sure to exclude your compilation stage from
these services.

Windows standalone program redistribution
=========================================

Whether compiling with MingW or MSVC, the standalone programs have
external dependencies to Visual C Runtime libraries. Nuitka tries to
ship those dependent DLLs by copying them from your system.

Beginning with Microsoft Windows 10, Microsoft ships ``ucrt.dll``
(Universal C Runtime libraries) which handles calls to
``api-ms-crt-*.dll``.

With earlier Windows platforms (and wine/ReactOS), you should consider
installing Visual C runtime libraries before executing a Nuitka
standalone compiled program.

Depending on the used C compiler, you'll need the following redist
versions on the target machines. However notice that compilation using
the 14.3 based version is recommended.

+------------------+-------------+-------------------------------+
| Visual C version | Redist Year | CPython                       |
+==================+=============+===============================+
| 14.3             | 2022        | 3.11                          |
+------------------+-------------+-------------------------------+
| 14.2             | 2019        | 3.5, 3.6, 3.7, 3.8, 3.9, 3.10 |
+------------------+-------------+-------------------------------+
| 14.1             | 2017        | 3.5, 3.6, 3.7, 3.8            |
+------------------+-------------+-------------------------------+
| 14.0             | 2015        | 3.5, 3.6, 3.7, 3.8            |
+------------------+-------------+-------------------------------+
| 10.0             | 2010        | 3.3, 3.4                      |
+------------------+-------------+-------------------------------+
| 9.0              | 2008        | 2.6, 2.7                      |
+------------------+-------------+-------------------------------+

When using MingGW64, you'll need the following redist versions:

+------------------+-------------+-------------------------------------+
| MingGW64 version | Redist Year | CPython                             |
+==================+=============+=====================================+
| 8.1.0            | 2015        | 3.5, 3.6, 3.7, 3.8, 3.9, 3.10, 3.11 |
+------------------+-------------+-------------------------------------+

Once the corresponding runtime libraries are installed on the target
system, you may remove all ``api-ms-crt-*.dll`` files from your Nuitka
compiled dist folder.

Detecting Nuitka at run time
============================

Nuitka does *not* ``sys.frozen`` unlike other tools, because it usually
triggers inferior code for no reason. For Nuitka, we have the module
attribute ``__compiled__`` to test if a specific module was compiled,
and the function attribute ``__compiled__`` to test if a specific
function was compiled.

Providing extra Options to Nuitka C compilation
===============================================

Nuitka will apply values from the environment variables ``CCFLAGS``,
``LDFLAGS`` during the compilation on top of what it determines to be
necessary. Beware of course, that is this is only useful if you know
what you are doing, so should this pose an issues, raise them only with
perfect information.

Producing a 32 bit binary on a 64 bit Windows system
====================================================

Nuitka will automatically target the architecture of the Python you are
using. If this is 64 bits, it will create a 64 bits binary, if it is 32
bits, it will create a 32 bits binary. You have the option to select the
bits when you download the Python. In the output of ``python -m nuitka
--version`` there is a line for the architecture. It ``Arch: x86_64``
for 64 bits, and just ``Arch: x86`` for 32 bits.

The C compiler will be picked to match that more or less automatically.
If you specify it explicitly and it mismatches, you will get a warning
about the mismatch and informed that you compiler choice was rejected.

********************
 Compilation Report
********************

When you use ``--report=compilation-report.xml`` Nuitka will create an
XML file with detailed information about the compilation and packaging
process. This is growing in completeness with very release and exposes
module usage attempts, timings of the compilation, plugin influences,
data file paths, DLLs, and reasons why things are included or not.

At this time, the report contains absolute paths in some places, with
your private information. The goal is to make this blended out by
default, because we also want to become able to compare compilation
reports from different setups, e.g. with updated packages, and see the
changes to Nuitka. The report is however recommended for your bug
reporting.

Also, another form is available, where the report is free form and
according to a Jinja2 template of yours, and one that is included in
Nuitka. The same information as used to produce the XML file is
accessible. However, right now this is not yet documented, but we plan
to add a table with the data. For reader of the source code that is
familiar with Jinja2, however, it will be easy to do it now already.

If you have a template, you can use it like this
``--report-template=your_template.rst.j2:your_report.rst`` and of
course, the usage of restructured text, is only an example. You can use
markdown, your own XML, or whatever you see fit. Nuitka will just expand
the template with the compilation report data.

Currently the follow reports are included in Nuitka. You just use the
name as a filename, and Nuitka will pick that one instead.

+---------------+--------------+--------------------------------------------------------+
| Report Name   | Status       | Purpose                                                |
+===============+==============+========================================================+
| LicenseReport | experimental | Distributions used in a compilation with license texts |
+---------------+--------------+--------------------------------------------------------+

.. note::

   The community can and should contribute more report types and help
   enhancing the existing ones for good looks.

*************
 Performance
*************

This chapter gives an overview, of what to currently expect in terms of
performance from Nuitka. It's a work in progress and is updated as we
go. The current focus for performance measurements is Python 2.7, but
3.x is going to follow later.

pystone results
===============

The results are the top value from this kind of output, running pystone
1000 times and taking the minimal value. The idea is that the fastest
run is most meaningful, and eliminates usage spikes.

.. code:: bash

   echo "Uncompiled Python2"
   for i in {1..100}; do BENCH=1 python2 tests/benchmarks/pystone.py ; done | sort -n | head -n 1
   python2 -m nuitka --lto=yes --pgo=yes tests/benchmarks/pystone.py
   echo "Compiled Python2"
   for i in {1..100}; do BENCH=1 ./pystone.bin ; done | sort -n | head -n 1

   echo "Uncompiled Python3"
   for i in {1..100}; do BENCH=1 python3 tests/benchmarks/pystone3.py ; done | sort -n | head -n 1
   python3 -m nuitka --lto=yes --pgo=yes tests/benchmarks/pystone3.py
   echo "Compiled Python3"
   for i in {1..100}; do BENCH=1 ./pystone3.bin ; done | sort -n | head -n 1

+-------------------+-------------------+----------------------+---------------------+
| Python            | Uncompiled        | Compiled LTO         | Compiled PGO        |
+===================+===================+======================+=====================+
| Debian Python 2.7 | 137497.87 (1.000) | 460995.20 (3.353)    | 503681.91 (3.663)   |
+-------------------+-------------------+----------------------+---------------------+
| Nuitka Python 2.7 | 144074.78 (1.048) | 479271.51 (3.486)    | 511247.44 (3.718)   |
+-------------------+-------------------+----------------------+---------------------+

******************
 Where to go next
******************

Remember, this project needs constant work. Although the Python
compatibility is insanely high, and test suite works near perfectly,
there is still more work needed, esp. to make it do more optimization.
Try it out, and when popular packages do not work, please make reports
on GitHub.

Follow me on Mastodon and Twitter
=================================

Nuitka announcements and interesting stuff is pointed to on both the
Mastodon and Twitter accounts, but obviously with not too many details,
usually pointing to the website, but sometimes I also ask questions
there.

`@KayHayen on Mastodon <https://fosstodon.org/@kayhayen>`_. `@KayHayen
on Twitter <https://twitter.com/KayHayen>`_.

Report issues or bugs
=====================

Should you encounter any issues, bugs, or ideas, please visit the
`Nuitka bug tracker <https://github.com/Nuitka/Nuitka/issues>`__ and
report them.

Best practices for reporting bugs:

-  Please always include the following information in your report, for
   the underlying Python version. You can easily copy&paste this into
   your report. It does contain more information that you think. Do not
   write something manually. You may always add of course.

   .. code:: bash

      python -m nuitka --version

-  Try to make your example minimal. That is, try to remove code that
   does not contribute to the issue as much as possible. Ideally come up
   with a small reproducing program that illustrates the issue, using
   ``print`` with different results when that programs runs compiled or
   native.

-  If the problem occurs spuriously (i.e. not each time), try to set the
   environment variable ``PYTHONHASHSEED`` to ``0``, disabling hash
   randomization. If that makes the problem go away, try increasing in
   steps of 1 to a hash seed value that makes it happen every time,
   include it in your report.

-  Do not include the created code in your report. Given proper input,
   it's redundant, and it's not likely that I will look at it without
   the ability to change the Python or Nuitka source and re-run it.

-  Do not send screenshots of text, that is bad and lazy. Instead,
   capture text outputs from the console.

Word of Warning
===============

Consider using this software with caution. Even though many tests are
applied before releases, things are potentially breaking. Your feedback
and patches to Nuitka are very welcome.

*************
 Join Nuitka
*************

You are more than welcome to join Nuitka development and help to
complete the project in all minor and major ways.

The development of Nuitka occurs in git. We currently have these 3
branches:

-  ``main``

   This branch contains the stable release to which only hotfixes for
   bugs will be done. It is supposed to work at all times and is
   supported.

-  ``develop``

   This branch contains the ongoing development. It may at times contain
   little regressions, but also new features. On this branch, the
   integration work is done, whereas new features might be developed on
   feature branches.

-  ``factory``

   This branch contains unfinished and incomplete work. It is very
   frequently subject to ``git rebase`` and the public staging ground,
   where my work for develop branch lives first. It is intended for
   testing only and recommended to base any of your own development on.
   When updating it, you very often will get merge conflicts. Simply
   resolve those by doing ``git fetch && git reset --hard
   origin/factory`` and switch to the latest version.

.. note::

   The `Developer Manual
   <https://nuitka.net/doc/developer-manual.html>`__ explains the coding
   rules, branching model used, with feature branches and hotfix
   releases, the Nuitka design and much more. Consider reading it to
   become a contributor. This document is intended for Nuitka users.

***********
 Donations
***********

Should you feel that you cannot help Nuitka directly, but still want to
support, please consider `making a donation
<https://nuitka.net/pages/donations.html>`__ and help this way.

***************************
 Unsupported functionality
***************************

The ``co_code`` attribute of code objects
=========================================

The code objects are empty for native compiled functions. There is no
bytecode with Nuitka's compiled function objects, so there is no way to
provide it.

PDB
===

There is no tracing of compiled functions to attach a debugger to.

**************
 Optimization
**************

Constant Folding
================

The most important form of optimization is the constant folding. This is
when an operation can be fully predicted at compile time. Currently,
Nuitka does these for some built-ins (but not all yet, somebody to look
at this more closely will be very welcome!), and it does it e.g. for
binary/unary operations and comparisons.

Constants currently recognized:

.. code:: python

   5 + 6  # binary operations
   not 7  # unary operations
   5 < 6  # comparisons
   range(3)  # built-ins

Literals are the one obvious source of constants, but also most likely
other optimization steps like constant propagation or function inlining
will be. So this one should not be underestimated and a very important
step of successful optimizations. Every option to produce a constant may
impact the generated code quality a lot.

.. admonition:: Status

   The folding of constants is considered implemented, but it might be
   incomplete in that not all possible cases are caught. Please report
   it as a bug when you find an operation in Nuitka that has only
   constants as input and is not folded.

Constant Propagation
====================

At the core of optimizations, there is an attempt to determine the
values of variables at run time and predictions of assignments. It
determines if their inputs are constants or of similar values. An
expression, e.g. a module variable access, an expensive operation, may
be constant across the module of the function scope and then there needs
to be none or no repeated module variable look-up.

Consider e.g. the module attribute ``__name__`` which likely is only
ever read, so its value could be predicted to a constant string known at
compile time. This can then be used as input to the constant folding.

.. code:: python

   if __name__ == "__main__":
       # Your test code might be here
       use_something_not_use_by_program()

.. admonition:: Status

   From modules attributes, only ``__name__`` is currently actually
   optimized. Also possible would be at least ``__doc__``. In the
   future, this may improve as SSA is expanded to module variables.

Built-in Name Lookups
=====================

Also, built-in exception name references are optimized if they are used
as a module level read-only variables:

.. code:: python

   try:
       something()
   except ValueError:  # The ValueError is a slow global name lookup normally.
       pass

.. admonition:: Status

   This works for all built-in names. When an assignment is done to such
   a name, or it's even local, then, of course, it is not done.

Built-in Call Prediction
========================

For built-in calls like ``type``, ``len``, or ``range`` it is often
possible to predict the result at compile time, esp. for constant inputs
the resulting value often can be precomputed by Nuitka. It can simply
determine the result or the raised exception and replace the built-in
call with that value, allowing for more constant folding or code path
reduction.

.. code:: python

   type("string")  # predictable result, builtin type str.
   len([1, 2])  # predictable result
   range(3, 9, 2)  # predictable result
   range(3, 9, 0)  # predictable exception, range raises due to 0.

.. admonition:: Status

   The built-in call prediction is considered implemented. We can simply
   during compile time emulate the call and use its result or raised
   exception. But we may not cover all the built-ins there are yet.

Sometimes the result of a built-in should not be predicted when the
result is big. A ``range()`` call e.g. may give too big values to
include the result in the binary. Then it is not done.

.. code:: python

   range(100000)  # We do not want this one to be expanded

.. admonition:: Status

   This is considered mostly implemented. Please file bugs for built-ins
   that are pre-computed, but should not be computed by Nuitka at
   compile time with specific values.

Conditional Statement Prediction
================================

For conditional statements, some branches may not ever be taken, because
of the condition truth value being possible to predict. In these cases,
the branch not taken and the condition check is removed.

This can typically predict code like this:

.. code:: python

   if __name__ == "__main__":
       # Your test code might be here
       use_something_not_use_by_program()

or

.. code:: python

   if False:
       # Your deactivated code might be here
       use_something_not_use_by_program()

It will also benefit from constant propagations, or enable them because
once some branches have been removed, other things may become more
predictable, so this can trigger other optimization to become possible.

Every branch removed makes optimization more likely. With some code
branches removed, access patterns may be more friendly. Imagine e.g.
that a function is only called in a removed branch. It may be possible
to remove it entirely, and that may have other consequences too.

.. admonition:: Status

   This is considered implemented, but for the maximum benefit, more
   constants need to be determined at compile time.

Exception Propagation
=====================

For exceptions that are determined at compile time, there is an
expression that will simply do raise the exception. These can be
propagated upwards, collecting potentially "side effects", i.e. parts of
expressions that were executed before it occurred, and still have to be
executed.

Consider the following code:

.. code:: python

   print(side_effect_having() + (1 / 0))
   print(something_else())

The ``(1 / 0)`` can be predicted to raise a ``ZeroDivisionError``
exception, which will be propagated through the ``+`` operation. That
part is just Constant Propagation as normal.

The call ``side_effect_having()`` will have to be retained though, but
the ``print`` does not and can be turned into an explicit raise. The
statement sequence can then be aborted and as such the
``something_else`` call needs no code generation or consideration
anymore.

To that end, Nuitka works with a special node that raises an exception
and is wrapped with a so-called "side_effects" expression, but yet can
be used in the code as an expression having a value.

.. admonition:: Status

   The propagation of exceptions is mostly implemented but needs
   handling in every kind of operations, and not all of them might do it
   already. As work progresses or examples arise, the coverage will be
   extended. Feel free to generate bug reports with non-working
   examples.

Exception Scope Reduction
=========================

Consider the following code:

.. code:: python

   try:
       b = 8
       print(range(3, b, 0))
       print("Will not be executed")
   except ValueError as e:
       print(e)

The ``try`` block is bigger than it needs to be. The statement ``b = 8``
cannot cause a ``ValueError`` to be raised. As such it can be moved to
outside the try without any risk.

.. code:: python

   b = 8
   try:
       print(range(3, b, 0))
       print("Will not be executed")
   except ValueError as e:
       print(e)

.. admonition:: Status

   This is considered done. For every kind of operation, we trace if it
   may raise an exception. We do however *not* track properly yet, what
   can do a ``ValueError`` and what cannot.

Exception Block Inlining
========================

With the exception propagation, it then becomes possible to transform
this code:

.. code:: python

   try:
       b = 8
       print(range(3, b, 0))
       print("Will not be executed!")
   except ValueError as e:
       print(e)

.. code:: python

   try:
       raise ValueError("range() step argument must not be zero")
   except ValueError as e:
       print(e)

Which then can be lowered in complexity by avoiding the raise and catch
of the exception, making it:

.. code:: python

   e = ValueError("range() step argument must not be zero")
   print(e)

.. admonition:: Status

   This is not implemented yet.

Empty Branch Removal
====================

For loops and conditional statements that contain only code without
effect, it should be possible to remove the whole construct:

.. code:: python

   for i in range(1000):
       pass

The loop could be removed, at maximum, it should be considered an
assignment of variable ``i`` to ``999`` and no more.

.. admonition:: Status

   This is not implemented yet, as it requires us to track iterators,
   and their side effects, as well as loop values, and exit conditions.
   Too much yet, but we will get there.

Another example:

.. code:: python

   if side_effect_free:
       pass

The condition check should be removed in this case, as its evaluation is
not needed. It may be difficult to predict that ``side_effect_free`` has
no side effects, but many times this might be possible.

.. admonition:: Status

   This is considered implemented. The conditional statement nature is
   removed if both branches are empty, only the condition is evaluated
   and checked for truth (in cases that could raise an exception).

Unpacking Prediction
====================

When the length of the right-hand side of an assignment to a sequence
can be predicted, the unpacking can be replaced with multiple
assignments.

.. code:: python

   a, b, c = 1, side_effect_free(), 3

.. code:: python

   a = 1
   b = side_effect_free()
   c = 3

This is of course only really safe if the left-hand side cannot raise an
exception while building the assignment targets.

We do this now, but only for constants, because we currently have no
ability to predict if an expression can raise an exception or not.

.. admonition:: Status

   This is partially implemented. We are working on unpacking
   enhancements, that will recognize where index access is available.
   This faster access will then avoid tuples and iteration, then this
   will be perfect.

Built-in Type Inference
=======================

When a construct like ``in xrange()`` or ``in range()`` is used, it is
possible to know what the iteration does and represent that so that
iterator users can use that instead.

I consider that:

.. code:: python

   for i in xrange(1000):
       something(i)

could translate ``xrange(1000)`` into an object of a special class that
does the integer looping more efficiently. In case ``i`` is only
assigned from there, this could be a nice case for a dedicated class.

.. admonition:: Status

   Future work, not even started.

Quicker Function Calls
======================

Functions are structured so that their parameter parsing and ``tp_call``
interface is separate from the actual function code. This way the call
can be optimized away. One problem is that the evaluation order can
differ.

.. code:: python

   def f(a, b, c):
       return a, b, c


   f(c=get1(), b=get2(), a=get3())

This will have to evaluate first ``get1()``, then ``get2()`` and only
then ``get3()`` and then make the function call with these values.

Therefore it will be necessary to have a staging of the parameters
before making the actual call, to avoid a re-ordering of the calls to
``get1()``, ``get2()``, and ``get3()``.

.. admonition:: Status

   Not even started. A re-formulation that avoids the dictionary to call
   the function, and instead uses temporary variables appears to be
   relatively straight forward once we do that kind of parameter
   analysis.

Lowering of iterated Container Types
====================================

In some cases, accesses to ``list`` constants can become ``tuple``
constants instead.

Consider that:

.. code:: python

   for x in [a, b, c]:
       something(x)

Can be optimized into this:

.. code:: python

   for x in (a, b, c):
       something(x)

This allows for simpler, faster code to be generated, and fewer checks
needed, because e.g. the ``tuple`` is clearly immutable, whereas the
``list`` needs a check to assert that. This is also possible for sets.

.. admonition:: Status

   Implemented, even works for non-constants. Needs other optimization
   to become generally useful, and will itself help other optimization
   to become possible. This allows us to e.g. only treat iteration over
   tuples, and not care about sets.

In theory, something similar is also possible for ``dict``. For the
later, it will be non-trivial though to maintain the order of execution
without temporary values introduced. The same thing is done for pure
constants of these types, they change to ``tuple`` values when iterated.

Metadata calls at compile time
==============================

Nuitka does not include metadata in the distribution. It's rather large,
and the goal is to use it at compile time. Therefore information about
entry points, version checks, etc. are all done at compile time rather
than at run time. Not only is that faster, it also recognized problems
sooner.

.. code:: python

   pkg_resources.require("lxml")
   importlib.metadata.version("lxml")
   ...

.. admonition:: Status

   This is considered complete. The coverage of the APIs is very good,
   but naturally this will always have to be code that uses compile time
   values, but that is nearly never an issue, and where it happens, we
   use "anti-bloat" patches to deal with these in 3rd party packages.

*************************
 Updates for this Manual
*************************

This document is written in REST. That is an ASCII format which is
readable to human, but easily used to generate PDF or HTML documents.

You will find the current version at:
https://nuitka.net/doc/user-manual.html
