Advanced Topics
================

The following discussions cover details of PyInstaller internal methods.
You should not need this level of detail for normal use,
but such details are helpful if you want to investigate
the PyInstaller code and possibly contribute to it,
as described in `How to Contribute`_.


.. _the bootstrap process in detail:

The Bootstrap Process in Detail
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

There are many steps that must take place before the bundled
script can begin execution.
A summary of these steps was given in the Overview
(:ref:`How the One-Folder Program Works` and
:ref:`How the One-File Program Works`).
Here is more detail to help you understand what the bootloader
does and how to figure out problems.


Bootloader
----------

The bootloader prepares everything for running Python code.
It begins the setup and then returns itself in another process.
This approach of using two processes allows a lot of flexibility
and is used in all bundles except one-folder mode in Windows.
So do not be surprised if you will see your bundled app
as  two processes in your system task manager.

What happens during execution of bootloader:

A. First process: bootloader starts.

    1. If one-file mode, extract bundled files to
       :file:`{temppath}/_MEI{xxxxxx}`.

    2. Modify various environment variables:

       - GNU/Linux: If set, save the original value of LD_LIBRARY_PATH
         into LD_LIBRARY_PATH_ORIG.
         Prepend our path to LD_LIBRARY_PATH.

       - AIX: same thing, but using LIBPATH and LIBPATH_ORIG.

       - OSX: unset DYLD_LIBRARY_PATH.

    3. Set up to handle signals for both processes.

    4. Run the child process.

    5. Wait for the child process to finish.

    6. If one-file mode, delete :file:`{temppath}/_MEI{xxxxxx}`.

B. Second process: bootloader itself started as a child process.

    1. On Windows set the `activation context`_.

    2. Load the Python dynamic library.
       The name of the dynamic library is embedded in the
       executable file.

    3. Initialize Python interpreter: set sys.path, sys.prefix, sys.executable.

    4. Run python code.

Running Python code requires several steps:

1. Run the Python initialization code which
   prepares everything for running the user's main script.
   The initialization code can use only the Python built-in modules
   because the general import mechanism is not yet available.
   It sets up the Python import mechanism to load modules
   only from archives embedded in the executable.
   It also adds the attributes ``frozen``
   and ``_MEIPASS`` to the :mod:`sys` built-in module.

2. Execute any run-time hooks: first those specified by the
   user, then any standard ones.

3. Install python "egg" files.
   When a module is part of a zip file (.egg),
   it has been bundled into the :file:`./eggs` directory.
   Installing means appending .egg file names to :data:`sys.path`.
   Python automatically detects whether an
   item in :data:`sys.path` is a zip file or a directory.

4. Run the main script.


Python imports in a bundled app
-------------------------------------

PyInstaller embeds compiled python code
(``.pyc`` files) within the executable.
PyInstaller injects its code into the
normal Python import mechanism.
Python allows this;
the support is described in :pep:`302`  "New Import Hooks".

PyInstaller implements the PEP 302 specification for
importing built-in modules,
importing "frozen" modules (compiled python code
bundled with the app) and for C-extensions.
The code can be read in :file:`./PyInstaller/loader/pyi_mod03_importers.py`.

At runtime the PyInstaller :pep:`302` hooks are appended
to the variable :data:`sys.meta_path`.
When trying to import modules the interpreter will
first try PEP 302 hooks in :data:`sys.meta_path`
before searching in :data:`sys.path`.
As a result, the Python interpreter
loads imported python modules from the archive embedded
in the bundled executable.

This is the resolution order of import statements
in a bundled app:

1. Is it a built-in module?
   A list of built-in modules is in variable
   :data:`sys.builtin_module_names`.

2. Is it a module embedded in the executable?
   Then load it from embedded archive.

3. Is it a C-extension?
   The app will try to find a file with name
   :file:`{package.subpackage.module}.pyd` or
   :file:`{package.subpackage.module}.so`.

4. Next examine paths in the :data:`sys.path`.
   There could be any additional location with python modules
   or ``.egg`` filenames.

5. If the module was not found then
   raise :class:`ImportError`.

Splash screen startup
-------------------------------------

.. Note::
    This feature is incompatible with macOS. In the current design, the
    splash screen operates in a secondary thread, which is disallowed by
    the Tcl/Tk (or rather, the underlying GUI toolkit) on macOS.


If a splash screen is enabled, the bootloader's startup procedure and
threading model is a little more complex. The following describes the
order of operation if splash screen is enabled:

1. Bootloader checks if it needs to display splash screen, i.e., if it
   is running in onedir mode or as a parent process in onefile mode.

2. If running in onefile mode, extract the splash screen dependencies
   (Tcl/Tk shared libraries and resources). The files are extracted to
   the application's temporary directory (:file:`{temppath}/_MEI{xxxxxx}`).

3. Tcl and Tk shared libraries are loaded into the booloader, and required
   Tcl/Tk symbols are bound.

    - Windows: ``tcl86t.dll`` / ``tk86t.dll``
    - Linux: ``libtcl.so`` / ``libtk.so``

4. Prepare a minimal environment for the `Tcl/Tk`_ interpreter
   by replacing/modifying the following functions:

    1. ``::tclInit``: This command is called to find the
       standard library of Tcl. We replace this command to
       force Tcl to load/execute only the bundled modules.

    2. ``::tcl_findLibrary``: Tk uses this function to source
       all its components. The overwritten function sets the
       required environment variable and evaluates the requested
       file.

    3. ``::exit``: This function is modified to ensure a
       proper exit of the splash screen thread.

    4. ``::source``: This command executes the contents of a
       passed file. Since we run in a minimal environment we
       mock the execution of not bundled files and execute
       those who are.

5. Start the Tcl interpreter and execute the splash screen
   script, which was generated by PyInstaller's build target
   :mod:`Splash` at build time. This script creates the
   environment variable :envvar:`_PYI_SPLASH_IPC`, which is also
   available to the python interpreter. It also initializes a
   TCP server socket to receive commands from python.

.. Note::
   The Tcl interpreter is started in a separate thread. Only
   after the Tcl interpreter has executed the splash
   screen script, the bootloader thread, which is responsible
   for extraction/starting the python interpreter, is
   resumed.


.. _bootloader environment variables:

Environment Variables Used by Frozen Applications
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

At run-time, PyInstaller's bootloader uses several environment variables.
Broadly speaking, these can be grouped into two categories: *public*
environment variables that allow user or application developer to
alter the behavior of the frozen application, and *private* environment
variables, which are used internally by the bootloader for inter-process
communication (for example, so that onefile parent process can communicate
the location of the temporary directory with extracted files to the child
process).

.. Note::
   PyInstaller-frozen applications use isolated instances of embedded
   python interpreter, and as such, do **not** process `environment variables
   used by python interpreter <https://docs.python.org/3/using/cmdline.html#environment-variables>`_.
   Some of these options can be (permanently) set at build time; see
   :ref:`specifying python interpreter options`.

Public environment variables
----------------------------

Public environment variables have ``PYINSTALLER_`` prefix. Currently,
the following variables are used:

.. envvar:: PYINSTALLER_SUPPRESS_SPLASH_SCREEN

  Setting this environment variable to 1 allows user to suppress splash
  screen in a splash-screen enabled application. This causes splash screen
  not to be shown, and functions of :mod:`pyi_splash` module become no-op
  without raising errors or warnings.

.. envvar:: PYINSTALLER_RESET_ENVIRONMENT

  Setting this environment variable to 1 causes the bootloader to reset
  all PyInstaller's internal environment variables, thus causing its
  process to be treated as a top-level process of a new instance of the
  application. In onefile mode, for example, this forces the application
  to unpack itself again.

  This environment variable is primarily intended for application developers
  that want to spawn subprocesses that outlive the current application
  process, for example, to implement :ref:`application restart <independent subprocess>`.

.. envvar:: PYINSTALLER_STRICT_UNPACK_MODE

  This environment variable being set to a value different than 0 turns
  on strict unpack mode for onefile applications. This turns file
  duplication issues and the failure to clean up the temporary files
  into fatal errors instead of warnings.

  This is primarily intended for use in PyInstaller's CI pipelines to
  automatically catch the afore-mentioned issues.

In onefile builds, the temporary directory location is also determined
by (system-wide) environment variable(s). See :ref:`defining the
extraction location` for OS-specific details.

Private environment variables
-----------------------------

Private environment variables have ``_PYI_`` prefix. They are used
internally by bootloader, primarily for communicating the settings and
the state between processes - the parent process (onefile), the main
application process, and any worker processes spawned via :data:`sys.executable`.

These environment variables should not be modified outside of the bootloader
code, as incorrect modification may break the frozen application (for example,
result in endless process spawn loop).

.. envvar:: _PYI_ARCHIVE_FILE

   Used to track the path to the archive file used by parent PyInstaller
   process (if any) and comparing it to the archive file of the current
   process, to determine if the executable has changed.

   If the environment variable is not set or if the path to archive file
   has changed, the current process is treated as a top-level process of
   the new instance of a PyInstaller-frozen application (i.e., all private
   environment variables are reset). This allows handling of scenarios when
   a onefile frozen application runs a different onefile frozen application
   in a subprocess; this second application must be started as a new
   instance of application (i.e., it needs to unpack itself into new
   temporary directory).

.. envvar:: _PYI_PARENT_PROCESS_LEVEL

   Used to track the process level, i.e., distinguish between the parent
   process (in onefile application), the main application process, and
   potential worker processes spawned via :data:`sys.executable`.

   If the environment variable is not defined, the process is considered
   to be a top-level process, i.e., a parent process of a onefile application,
   or main application process of a onedir application process. This process
   then sets the environment variable to inform the child process of its
   type, i.e., main application process of a onefile application or a
   worker sub-process of a onedir application. In case of onefile application,
   the  main application process again modifies the environment variable to
   inform its child processes of their type, i.e., worker sub-processes.

.. envvar:: _PYI_LINUX_PROCESS_NAME

   Used to copy the name of the top-level onefile process (the parent
   process) to child processes, via the ``prctl`` syscall with
   ``PR_GET_NAME`` and ``PR_SET_NAME``.

.. envvar:: _PYI_APPLICATION_HOME_DIR

   Used by the top-level onefile process (the parent process) to communicate
   the location of the application's temporary directory to the main
   application process. The main application process copies this path to the
   PyInstaller-specific ``sys._MEIPASS`` attribute.

.. envvar:: _PYI_SPLASH_IPC

   Set by splash-screen enabled application to to communicate the splash
   screen's IPC port to the :mod:`pyi_splash` module.

   The environment variable is set by the splash screen's Tcl script, which
   runs in auxiliary thread of a onefile application's parent process or
   onedir application's main application process. It is read by the :mod:`pyi_splash`
   module, which typically runs in the main application process.

   For worker processes spawned via :data:`sys.executable`, the value is
   set to 0, which signals to :mod:`pyi_splash` that splash screen is
   suppressed in this particular (sub)process. Similarly, the bootloader
   sets the value of this environment variable to 0 if splash screen is
   suppressed via the public :envvar:`PYINSTALLER_SUPPRESS_SPLASH_SCREEN`
   environment variable.


.. _pyi_splash Module:

:mod:`pyi_splash` Module (Detailed)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This module connects to the bootloader to send messages to the splash screen.

It is intended to act as an RPC interface for the functions provided by the
bootloader, such as displaying text or closing. This makes the users python
program independent of how the communication with the bootloader is
implemented, since a consistent API is provided.

To connect to the bootloader, it connects to a local tcp server socket whose port
is passed through the environment variable :envvar:`_PYI_SPLASH_IPC`. The bootloader
connects to the socket via the python module ``_socket``. Although this socket
is bidirectional, the module is only configured to send data.
Since the os-module, which is needed to request the environment variable,
is not available at boot time, the module does not establish the connection
until initialization.

This module does not support reloads while the splash screen is displayed, i.e.
it cannot be reloaded (such as by :func:`importlib.reload`), because the splash
screen closes automatically when the connection to this instance of the
module is lost.

.. Note::
    The splash screen might be gracefully disabled in some types of processes
    (for example, worker sub-processes spawned by the main application process).
    In addition, user can explicitly request splash screen to be suppressed
    at run-time by setting the :envvar:`PYINSTALLER_SUPPRESS_SPLASH_SCREEN` environment
    variable to ``1``. In such cases, the ``pyi_splash`` module can still be
    imported but its functions are all no-op.

Functions
---------

.. py:module:: pyi_splash
.. py:currentmodule:: pyi_splash

.. Note::
    Note that if the :envvar:`_PYI_SPLASH_IPC` environment variable does not exist or an
    error occurs during the connection, the module will **not** raise an error, but simply
    not initialize itself (i.e. :func:`pyi_splash.is_alive` will return ``False``). Before
    sending commands to the splash screen, one should check if the module was initialized
    correctly, otherwise a :class:`RuntimeError` will be raised.

.. py:function:: is_alive()

    Indicates whether the module can be used.

    Returns ``False`` if the module is either not initialized or was disabled
    by closing the splash screen. Otherwise, the module should be usable.

.. py:function:: update_text(msg)

    Updates the text on the splash screen window.

    :param str msg: the text to be displayed
    :raises ConnectionError: If the OS fails to write to the socket
    :raises RuntimeError: If the module is not initialized

.. py:function:: close()

    Close the connection to the ipc tcp server socket

    This will close the splash screen and renders this module unusable.
    After this function is called, no connection can be opened to the splash
    screen again and all functions if this module become unusable


.. _the toc and tree classes:

The Table of Contents (TOC) lists and the Tree Class
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

PyInstaller manages lists of files that are to be collected in the
so-called Table of Contents (TOC) list format. These lists contain
three-element tuples that encapsulate information about a file's
destination name, the file's full source path, and its type.

As part of utilities for managing the TOC lists, PyInstaller provides
a ``Tree`` class as a convenient way to build a TOC list from the
contents of the given directory. This utility class can be used either
in the :ref:`.spec files <using spec files>` file or from custom hooks.


Table of Contents (TOC) lists
-----------------------------

The ``Analysis`` object produces several TOC lists that provide information
about files to be collected. The files are grouped into distinct lists
based on their type or function, for example:
- ``Analysis.scripts``: program script(s)
- ``Analysis.pure``: pure-python modules
- ``Analysis.binaries``: binary extension modules and shared libraries
- ``Analysis.datas``: data files

The generated TOC lists are passed to various build targets within the
:ref:`spec file <using spec files>`, such as ``PYZ``, ``EXE``, and
``COLLECT``.

Each TOC list contains three-element tuples,

    ``(dest_name, src_name , typecode)``

where ``dest_name`` is the destination file name (i.e., file name within
the frozen application; as such, it must always be a relative name),
``src_name`` is the source file name (the path from where the file is
collected), and ``typecode`` is a string that denotes the type of the
file (or entry).

Internally, PyInstaller uses a number of *typecode* values, but for the
normal case you need to know only these:

+---------------+---------------------------------------+----------------------------------+---------------------------------------------+
| **typecode**  | **description**                       | **dest_name**                    | **src_name**                                |
+===============+=======================================+==================================+=============================================+
| 'DATA'        | Arbitrary (data) files.               | Name in the frozen application.  | Full path to the file on the build system.  |
+---------------+---------------------------------------+----------------------------------+---------------------------------------------+
| 'BINARY'      | A shared library.                     | Name in the frozen application.  | Full path to the file on the build system.  |
+---------------+---------------------------------------+----------------------------------+---------------------------------------------+
| 'EXTENSION'   | A Python binary extension.            | Name in the frozen application.  | Full path to the file on the build system.  |
+---------------+---------------------------------------+----------------------------------+---------------------------------------------+
| 'OPTION'      | A PyInstaller/Python run-time option. | Option name (and optional value, | Ignored.                                    |
|               |                                       | separated by a whitespace).      |                                             |
+---------------+---------------------------------------+----------------------------------+---------------------------------------------+

The destination name corresponds to the name of the final in the
frozen application, relative to the top-level application directory.
It may include path elements, for example :file:`extras/mydata.txt`.

Entries of type ``BINARY`` and ``EXTENSION`` are assumed to represent a
file containing loadable executable code, such as a dynamic library.
Generally, ``EXTENSION`` is used to denote Python extensions modules,
such as modules compiled by Cython_. The two file types are treated in
the same way; PyInstaller scans them for additional link-time
dependencies and collects any dependencies that are discovered. On some
operating systems, binaries and extensions undergo additional processing
(such as path rewriting for link-time dependencies and code-signing
on macOS).

The TOC lists produced by ``Analysis`` can be modified in the
:ref:`spec file <using spec files>` file before they are passed on to
the build targets to either include additional entries (although it is
preferable to pass extra files to be included via `binaries` or `datas`
arguments of `Analysis`) or remove unwanted entries.

.. versionchanged:: 5.11

   In PyInstaller versions prior to 5.11, the TOC lists were in fact
   instances of the :class:`TOC` class, which internally performed
   implicit entry de-duplication; i.e., trying to insert an entry with
   existing target name would result in no changes to the list.

   However, due to the shortcomings of the ``TOC`` class that resulted from
   loosely-defined and conflicting semantics, the use of the ``TOC`` class
   has been deprecated. The TOC lists are now instances of plain ``list``,
   and PyInstaller performs explicit list normalization (entry de-duplication).
   The explicit normalization is performed at the end of ``Analysis``
   instantiation, when the lists are stored in the class' properties (such
   as ``Analysis.datas`` and ``Analysis.binaries``). Similarly, explicit
   list normalization is also performed once the build targets (``EXE``,
   ``PYZ``, ``PKG``, ``COLLECT``, ``BUNDLE``) consolidate the input TOC
   lists into the final list.


The Tree Class
--------------

The ``Tree`` class offers a convenient way of creating a TOC list that
describes contents of the given directory:

      ``Tree(``\ *root*\ ``, prefix=``\ *run-time-folder*\ ``, excludes=``\ *string_list*\ ``, typecode=``\ *code* | ``'DATA' )``

* The *root* argument is a string denoting the path to the directory.
  It may be absolute or relative to the spec file directory.

* The optional *prefix* argument is a name for a sub-directory
  in the application directory into which files are to be collected.
  If not specified or set to ``None``, the files will be collected
  into the top-level application directory.

* The optional *excludes* argument is a list of one or more
  strings that match files in the *root* that should be omitted from the Tree.
  An item in the list can be either:

  - a name, which causes files or folders with this basename to be excluded

  - a glob pattern (e.g., ``*.ext``), which causes matching files to be excluded

* The optional *typecode* argument specifies the TOC typecode string
  that is assigned to all entries in the TOC list.
  The default value is ``DATA``, which is appropriate for most cases.

For example::

    extras_toc = Tree('../src/extras', prefix='extras', excludes=['tmp', '*.pyc'])

This creates ``extras_toc`` as a TOC list that contains entries for
all files from the relative path :file:`../src/extras`,
omitting those that have the basename (or are in a folder named) ``tmp``
or have the ``.pyc`` extension.
Each tuple in this TOC has:

* A *dest_name* in form of:file:`extras/{filename}`.

* A *src_name* that corresponds to the full absolute path to that file in the
  :file:`../src/extras` folder (relative to the location of the spec file).

* A *typecode* of ``DATA`` (the default).

An example of creating a TOC listing some binary modules::

    cython_mods = Tree('..src/cy_mods', excludes=['*.pyx', '*.py', '*.pyc'], typecode='EXTENSION')

This creates a TOC list with entries for each file in the :file:`cy_mods` directory,
excluding files with the ``.pyx``, ``.py``, or ``.pyc`` extension
(so presumably collecting only the ``.pyd`` or ``.so`` modules created by Cython).
Each tuple in this TOC has:

* A *dest_name* that corresponds to the file's basename (all files are collected
  in top-level application directory).

* A *src_name* that corresponds to the full absolute path to that file in
  :file:`../src/cy_mods` relative to the spec file.

* A *typecode* of ``EXTENSION`` (``BINARY`` could be used as well).


.. _inspecting archives:

Inspecting Archives
~~~~~~~~~~~~~~~~~~~~~~

An archive is a file that contains other files,
for example a ``.tar`` file, a ``.jar`` file, or a ``.zip`` file.
Two kinds of archives are used in PyInstaller.
One is a ZlibArchive, which
allows Python modules to be stored efficiently and,
with some import hooks, imported directly.
The other, a CArchive, is similar to a ``.zip`` file,
a general way of packing up (and optionally compressing) arbitrary blobs of data.
It gets its name from the fact that it can be manipulated easily from C
as well as from Python.
Both of these derive from a common base class, making it fairly easy to
create new kinds of archives.


ZlibArchive
--------------

A ZlibArchive contains compressed ``.pyc`` or ``.pyo`` files.
The ``PYZ`` class invocation in a spec file creates a ZlibArchive.

The table of contents in a ZlibArchive
is a Python dictionary that associates a key,
which is a member's name as given in an ``import`` statement,
with a seek position and a length in the ZlibArchive.
All parts of a ZlibArchive are stored in the
`marshalled`_ format and so are platform-independent.

A ZlibArchive is used at run-time to import bundled python modules.
Even with maximum compression this works  faster than the normal import.
Instead of searching :data:`sys.path`, there's a lookup in the dictionary.
There are no directory operations and no
file to open (the file is already open).
There's just a seek, a read and a decompress.

A Python error trace will point to the source file from which the archive
entry was created (the ``__file__`` attribute from the time the
``.pyc`` was compiled, captured and saved in the archive).
This will not tell your user anything useful,
but if they send you a Python error trace,
you can make sense of it.

.. figure:: _static/ZlibArchive.png
   :alt: Structure of the ZlibArchive

   Structure of the ZlibArchive


CArchive
-------------

A CArchive can contain any kind of file.
It's very much like a ``.zip`` file.
They are easy to create in Python and easy to unpack from C code.
A CArchive can be appended to another file, such as
an ELF and COFF executable.
To allow this, the archive is made with its table of contents at the
end of the file, followed only by a cookie that tells where the
table of contents starts and
where the archive itself starts.

A CArchive can be embedded within another CArchive.
An inner archive can be opened and used in place,
without having to extract it.

Each table of contents entry has variable length.
The first field in the entry gives the length of the entry.
The last field is the name of the corresponding packed file.
The name is null terminated.
Compression is optional for each member.

There is also a type code associated with each member.
The type codes are used by the self-extracting executables.
If you're using a ``CArchive`` as a ``.zip`` file, you don't need to worry about the code.

The ELF executable format (Windows, GNU/Linux and some others) allows arbitrary
data to be concatenated to the end of the executable without disturbing its
functionality. For this reason, a CArchive's Table of Contents is
at the end of the archive. The executable can open itself as a binary
file, seek to the end and 'open' the CArchive.

.. figure:: _static/CArchive.png
   :alt: CArchive

   Structure of the CArchive

.. figure:: _static/SE_exe.png
   :alt: Structure of the Self Extracting Executable

   Structure of the Self Extracting Executable


Using pyi-archive_viewer
--------------------------

Use the ``pyi-archive_viewer`` command to inspect any type of archive:

      ``pyi-archive_viewer`` *archivefile*

With this command you can examine the contents of any archive built with
PyInstaller (a ``PYZ`` or ``PKG``), or any executable (``.exe`` file
or an ELF or COFF binary).
The archive can be navigated using these commands:

O *name*
    Open the embedded archive *name* (will prompt if omitted).
    For example when looking in a one-file executable, you
    can open the ``PYZ-00.pyz`` archive inside it.

U
    Go up one level (back to viewing the containing archive).

X *name*
    Extract *name* (will prompt if omitted).
    Prompts for an output filename.
    If none given, the member is extracted to stdout.

Q
    Quit.

The ``pyi-archive_viewer`` command has these options:

-h, --help
    Show help.

-l, --log
    Quick contents log.

-b, --brief
    Print a python evaluable list of contents filenames.

-r, --recursive
    Used with -l or -b, applies recursive behaviour.



.. _inspecting executables:

Inspecting Executables
~~~~~~~~~~~~~~~~~~~~~~~~

You can inspect any executable file with ``pyi-bindepend``:

    ``pyi-bindepend`` *executable_or_dynamic_library*

The ``pyi-bindepend`` command analyzes the executable or DLL you name
and writes to stdout all its binary dependencies.
This is handy to find out which DLLs are required by
an executable or by another DLL.

``pyi-bindepend`` is used by PyInstaller to
follow the chain of dependencies of binary extensions
during Analysis.


.. _creating a reproducible build:

Creating a Reproducible Build
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In certain cases it is important that when you build the same application twice,
using exactly the same set of dependencies,
the two bundles should be exactly, bit-for-bit identical.

That is not the case normally.
Python uses a random hash to make dicts and other hashed types,
and this affects compiled byte-code as well as PyInstaller
internal data structures.
As a result, two builds may not produce bit-for-bit identical results
even when all the components of the application bundle are the same
and the two applications execute in identical ways.

You can ensure that a build will produce the same bits
by setting the :envvar:`PYTHONHASHSEED` environment variable to a known
integer value before running PyInstaller.
This forces Python to use the same random hash sequence until
:envvar:`PYTHONHASHSEED` is unset or set to ``'random'``.
For example, execute PyInstaller in a script such as
the following (for GNU/Linux and macOS)::

    # set seed to a known repeatable integer value
    PYTHONHASHSEED=1
    export PYTHONHASHSEED
    # create one-file build as myscript
    pyinstaller myscript.spec
    # make checksum
    cksum dist/myscript/myscript | awk '{print $1}' > dist/myscript/checksum.txt
    # let Python be unpredictable again
    unset PYTHONHASHSEED

.. versionchanged:: 4.8
   The build timestamp in the PE headers of the generated Windows
   executables is set to the current time during the assembly process.
   A custom timestamp value can be specified via the ``SOURCE_DATE_EPOCH``
   environment variable to achieve `reproducible builds
   <https://reproducible-builds.org/docs/source-date-epoch>`_.


.. include:: _common_definitions.txt

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