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

.. image:: doc/images/Nuitka-Logo-Symbol.png

.. contents::

.. raw:: pdf

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**********
 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 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 ``gcc`` compiler of at least version 5.1, or the ``g++``
      compiler of at least version 4.4 as an alternative.

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

   -  The MinGW64 C11 compiler on Windows, must be based on gcc 8 or
      higher. It will be automatically downloaded if not found, which is
      the recommended way of installing it.

   -  Visual Studio 2019 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 that language).

   -  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

   .. admonition:: 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 (on Windows via
      registry) and you shouldn't notice it as long as they are
      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.

      On Windows, for Python not installed system-wide and acceleration
      mode, you need to copy the ``PythonXX.DLL`` alongside it,
      something Nuitka does automatically.

   .. 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 (32/64
   bits).

   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
   http://www.visualstudio.com/en-us/downloads/download-visual-studio-vs.aspx
   (the Express editions work just fine).

   The latest version is recommended but not required. On the other hand,
   there is no need to except pre-Windows 10 support, 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
<http://www.nuitka.net/pages/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 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 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 --mingw64 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. Say yes to those.

If you like to have full output from the C compilation add
``--show-scons``, but that should only be useful if you have errors.

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-imports`` and other variants work as well, but
   the included modules will only become importable *after* you imported
   the ``some_module`` name.

.. 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 recursion into the package directory needs to be provided
   manually, otherwise, the package is empty. Data files located inside
   the package will not be embedded yet.

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

Follow 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
runtime.

For data files to be included, use the option
``--include-data-file=<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-file=/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.

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, which on Linux will not even unpack
itself, but instead loop back mount its contents as a filesystem and use
that.

On Windows, there are two modes, one which is copying it to the AppData
of your company specified, to also use it as a cache, and one which does
it in the temporary directory. You need to do one this this.

.. code:: bash

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

.. note::

   There are more Windows specific options, e.g. related to icons, but
   also more version information, consider the ``--help`` output for the
   details of these.

Again, on Windows, for the temporary file directory, by default the user
one is used, however this is overridable with a path specification given
in ``--windows-onefile-tempdir-spec=%TEMP%\\onefile_%PID%_%TIME%`` which
is the default and asserts that the temporary directories created cannot
collide.

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 filename of executable. | C:\SomeWhere\YourOnefile.exe      |
+-----------+--------------------------------------+-----------------------------------+

.. 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.

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

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

If your script modifies ``sys.path`` to e.g. insert directories with
source code relative to it, Nuitka will currently not be able to see
those. However, if you set the ``PYTHONPATH`` to the resulting value,
you will be able to compile it.

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

If your program fails to file data, it can cause all kinds of different
behaviours, 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.

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.

For now, a major weapon in fighting dependency creap 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 ``--enable-plugin=anti-bloat
--noinclude-pytest-mode=nofollow --noinclude-setuptools-mode=nofollow``
and check its help output. It can take for each module of your choice,
e.g. forcing also that PyQt5 is considered uninstalled for standalone
mode.

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 ``--windows-disable-console`` or use the
options ``--windows-force-stdout-spec`` and
``--windows-force-stderr-spec`` with paths as documented for
``--windows-onefile-tempdir-spec`` above.

******
 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.

+------------------+--------------------------------------+--------------------------------+
| Variable         | What this Expands to                 | Example                        |
+==================+======================================+================================+
| {OS}             | Name of the OS used                  | Linux, Windows, Darwin,        |
|                  |                                      | FreeBSD, OpenBSD               |
+------------------+--------------------------------------+--------------------------------+
| {Version}        | Version of Nuitka                    | (0, 6, 14)                     |
+------------------+--------------------------------------+--------------------------------+
| {Arch}           | Architecture used                    | x86_64, arm64, etc.            |
+------------------+--------------------------------------+--------------------------------+
| {MAIN_DIRECTORY} | Directory of the compiled file       | some_dir/maybe_relative        |
+------------------+--------------------------------------+--------------------------------+

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.

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.

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 redistribuation
==========================================

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 rehook 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:

+------------------+-------------+-------------------------+
| Visual C version | Redist Year | CPython                 |
+==================+=============+=========================+
| 14.2             | 2019        | 3.5, 3.6, 3.7, 3.8, 3.9 |
+------------------+-------------+-------------------------+
| 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 |
+------------------+-------------+-------------------------+

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
============================

It doesn't set ``sys.frozen`` unlike other tools. For Nuitka, we have
the module attribute ``__compiled__`` to test if a specific module was
compiled.

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

Remember, this project is not completed yet. Although the CPython test
suite works near perfect, there is still more work needed, esp. to make
it do more optimization. Try it out.

Follow me on Twitter
====================

Nuitka announcements and interesting stuff is pointed to on the Twitter
account, but obviously with no details. `@KayHayen
<https://twitter.com/KayHayen>`_.

I will not answer Nuitka issues via Twitter though, rather make
occasional polls, and give important announcements, as well as low-level
posts about development ongoing.

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

Should you encounter any issues, bugs, or ideas, please visit the
`Nuitka bug tracker <https://github.com/kayhayen/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.

   .. code:: sh

      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:

-  ``master``

   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 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 conditions 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

   Not implemented yet. Will need us to see through the unpacking of
   what is an iteration over a tuple, we created ourselves. We are not
   there yet, but we will get there.

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.

*********
 Credits
*********

Contributors to Nuitka
======================

Thanks go to these individuals for their much-valued contributions to
Nuitka.

The order is sorted by time.

-  Li Xuan Ji: Contributed patches for general portability issue and
   enhancements to the environment variable settings.

-  Nicolas Dumazet: Found and fixed reference counting issues,
   ``import`` packages work, improved some of the English and generally
   made good code contributions all over the place, solved code
   generation TODOs, did tree building cleanups, core stuff.

-  Khalid Abu Bakr: Submitted patches for his work to support MinGW and
   Windows, debugged the issues, and helped me to get cross compile with
   MinGW from Linux to Windows. This was quite difficult stuff.

-  Liu Zhenhai: Submitted patches for Windows support, making the inline
   Scons copy actually work on Windows as well. Also reported import
   related bugs, and generally helped me make the Windows port more
   usable through his testing and information.

-  Christopher Tott: Submitted patches for Windows, and general as well
   as structural cleanups.

-  Pete Hunt: Submitted patches for macOS X support.

-  "ownssh": Submitted patches for built-ins module guarding, and made
   massive efforts to make high-quality bug reports. Also the initial
   "standalone" mode implementation was created by him.

-  Juan Carlos Paco: Submitted cleanup patches, creator of the `Nuitka
   GUI <https://github.com/juancarlospaco/nuitka-gui>`__, creator of the
   `Ninja IDE plugin <https://github.com/juancarlospaco/nuitka-ninja>`__
   for Nuitka.

-  "Dr. Equivalent": Submitted the Nuitka Logo.

-  Johan Holmberg: Submitted patch for Python3 support on macOS X.

-  Umbra: Submitted patches to make the Windows port more usable, adding
   user provided application icons, as well as MSVC support for large
   constants and console applications.

-  David Cortesi: Submitted patches and test cases to make macOS port
   more usable, specifically for the Python3 standalone support of Qt.

-  Andrew Leech: Submitted github pull request to allow using "-m
   nuitka" to call the compiler. Also pull request to improve
   "bist_nuitka" and to do the registration.

-  Paweł K: Submitted github pull request to remove glibc from
   standalone distribution, saving size and improving robustness
   considering the various distributions.

-  Orsiris de Jong: Submitted github pull request to implement the
   dependency walking with ``pefile`` under Windows. Also provided the
   implementation of Dejong Stacks.

-  Jorj X. McKie: Submitted github pull requests with NumPy plugin to
   retain its accelerating libraries, and Tkinter to include the TCL
   distribution on Windows.

Projects used by Nuitka
=======================

-  The `CPython project <http://www.python.org>`__

   Thanks for giving us CPython, which is the base of Nuitka. We are
   nothing without it.

-  The `GCC project <http://gcc.gnu.org>`__

   Thanks for not only the best compiler suite but also thanks for
   making it easy supporting to get Nuitka off the ground. Your compiler
   was the first usable for Nuitka and with very little effort.

-  The `Scons project <http://www.scons.org>`__

   Thanks for tackling the difficult points and providing a Python
   environment to make the build results. This is such a perfect fit to
   Nuitka and a dependency that will likely remain.

-  The `valgrind project <http://valgrind.org>`__

   Luckily we can use Valgrind to determine if something is an actual
   improvement without the noise. And it's also helpful to determine
   what's actually happening when comparing.

-  The `NeuroDebian project <http://neuro.debian.net>`__

   Thanks for hosting the build infrastructure that the Debian and
   sponsor Yaroslav Halchenko uses to provide packages for all Ubuntu
   versions.

-  The `openSUSE Buildservice <http://openbuildservice.org>`__

   Thanks for hosting this excellent service that allows us to provide
   RPMs for a large variety of platforms and make them available
   immediately nearly at release time.

-  The `MinGW64 project <http://mingw-w64.org>`__

   Thanks for porting the gcc to Windows. This allowed portability of
   Nuitka with relatively little effort.

-  The `Buildbot project <http://buildbot.net>`__

   Thanks for creating an easy to deploy and use continuous integration
   framework that also runs on Windows and is written and configured in
   Python code. This allows running the Nuitka tests long before release
   time.

-  The `isort project <http://timothycrosley.github.io/isort/>`__

   Thanks for making nice import ordering so easy. This makes it so easy
   to let your IDE do it and clean up afterward.

-  The `black project <https://github.com/ambv/black>`__

   Thanks for making a fast and reliable way for automatically
   formatting the Nuitka source code.

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

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

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

And the current PDF under: https://nuitka.net/doc/README.pdf
