[Python-Dev] PEP 587 "Python Initialization Configuration" version 4

Victor Stinner vstinner at redhat.com
Mon May 20 08:05:42 EDT 2019


I expected the version 3 of my PEP to be complete, but Gregory Szorc
and Steve Dower spotted a few more issues ;-)

The main change of the version 4 is the introduction of "Python
Configuration" and "Isolated Configuration" default configuration
which are well better defined.

The new "Isolated Configuration" provides sane default values to
isolate Python from the system. For example, to embed Python into an
application. Using the environment are now opt-in options, rather than
an opt-out options. For example, environment variables, command line
arguments and global configuration variables are ignored by default.

Building a customized Python which behaves as the regular Python
becomes easier using the new Py_RunMain() function. Moreover, using
the "Python Configuration", PyConfig.argv arguments are now parsed the
same way the regular Python parses command line arguments, and
PyConfig.xoptions are handled as -X opt command line options.

I replaced all macros with functions. Macros can cause issues when
used from different programming languages, whereas functions are
always well supported.

PyPreConfig structure doesn't allocate memory anymore (the allocator
field becomes an integer, instead of a string). I removed the
"Constant PyConfig" special case which introduced too many exceptions
for little benefit.

See the "Version History" section for the full changes.

HTML version:

Full text below.


PEP: 587
Title: Python Initialization Configuration
Author: Victor Stinner <vstinner at redhat.com>, Nick Coghlan <ncoghlan at gmail.com>
BDFL-Delegate: Thomas Wouters <thomas at python.org>
Discussions-To: python-dev at python.org
Status: Draft
Type: Standards Track
Content-Type: text/x-rst
Created: 27-Mar-2019
Python-Version: 3.8


Add a new C API to configure the Python Initialization providing finer
control on the whole configuration and better error reporting.

It becomes possible to read the configuration and then override some
computed parameters before it is applied. It also becomes possible to
completely override how Python computes the module search paths

The new `Isolated Configuration`_ provides sane default values to
isolate Python from the system. For example, to embed Python into an
application. Using the environment are now opt-in options, rather than
an opt-out options. For example, environment variables, command line
arguments and global configuration variables are ignored by default.

Building a customized Python which behaves as the regular Python becomes
easier using the new ``Py_RunMain()`` function. Moreover, using the
`Python Configuration`_, ``PyConfig.argv`` arguments are now parsed the
same way the regular Python parses command line arguments, and
``PyConfig.xoptions`` are handled as ``-X opt`` command line options.

This extracts a subset of the API design from the PEP 432 development
and refactoring work that is now considered sufficiently stable to make
public (allowing 3rd party embedding applications access to the same
configuration APIs that the native CPython CLI is now using).


Python is highly configurable but its configuration evolved organically.
The initialization configuration is scattered all around the code using
different ways to set them: global configuration variables (ex:
``Py_IsolatedFlag``), environment variables (ex: ``PYTHONPATH``),
command line arguments (ex: ``-b``), configuration files (ex:
``pyvenv.cfg``), function calls (ex: ``Py_SetProgramName()``). A
straightforward and reliable way to configure Python is needed.

Some configuration parameters are not accessible from the C API, or not
easily. For example, there is no API to override the default values of

Some options like ``PYTHONPATH`` can only be set using an environment
variable which has a side effect on Python child processes if not unset

Some options also depends on other options: see `Priority and Rules`_.
Python 3.7 API does not provide a consistent view of the overall

The C API of Python 3.7 Initialization takes ``wchar_t*`` strings as
input whereas the Python filesystem encoding is set during the
initialization which can lead to mojibake.

Python 3.7 APIs like ``Py_Initialize()`` aborts the process on memory
allocation failure which is not convenient when Python is embedded.
Moreover, ``Py_Main()`` could exit directly the process rather than
returning an exit code. Proposed new API reports the error or exit code
to the caller which can decide how to handle it.

Implementing the PEP 540 (UTF-8 Mode) and the new ``-X dev`` correctly
was almost impossible in Python 3.6. The code base has been deeply
reworked in Python 3.7 and then in Python 3.8 to read the configuration
into a structure with no side effect. It becomes possible to clear the
configuration (release memory) and read again the configuration if the
encoding changed . It is required to implement properly the UTF-8 which
changes the encoding using ``-X utf8`` command line option. Internally,
bytes ``argv`` strings are decoded from the filesystem encoding. The
``-X dev`` changes the memory allocator (behaves as
``PYTHONMALLOC=debug``), whereas it was not possible to change the
memory allocation *while* parsing the command line arguments. The new
design of the internal implementation not only allowed to implement
properly ``-X utf8`` and ``-X dev``, it also allows to change the Python
behavior way more easily, especially for corner cases like that, and
ensure that the configuration remains consistent: see `Priority and

This PEP is a partial implementation of PEP 432 which is the overall
design.  New fields can be added later to ``PyConfig`` structure to
finish the implementation of the PEP 432 (e.g. by adding a new partial
initialization API which allows to configure Python using Python objects to
finish the full initialization). However, those features are omitted from this
PEP as even the native CPython CLI doesn't work that way - the public API
proposal in this PEP is limited to features which have already been implemented
and adopted as private APIs for us in the native CPython CLI.

Python Initialization C API

This PEP proposes to add the following new structures, functions and

New structures:

* ``PyConfig``
* ``PyInitError``
* ``PyPreConfig``
* ``PyWideStringList``

New functions:

* ``PyConfig_Clear(config)``
* ``PyConfig_InitIsolatedConfig()``
* ``PyConfig_InitPythonConfig()``
* ``PyConfig_Read(config)``
* ``PyConfig_SetArgv(config, argc, argv)``
* ``PyConfig_SetBytesArgv(config, argc, argv)``
* ``PyConfig_SetBytesString(config, config_str, str)``
* ``PyConfig_SetString(config, config_str, str)``
* ``PyInitError_Error(err_msg)``
* ``PyInitError_Exit(exitcode)``
* ``PyInitError_Failed(err)``
* ``PyInitError_IsError(err)``
* ``PyInitError_IsExit(err)``
* ``PyInitError_NoMemory()``
* ``PyInitError_Ok()``
* ``PyPreConfig_InitIsolatedConfig(preconfig)``
* ``PyPreConfig_InitPythonConfig(preconfig)``
* ``PyWideStringList_Append(list, item)``
* ``PyWideStringList_Insert(list, index, item)``
* ``Py_BytesMain(argc, argv)``
* ``Py_ExitInitError(err)``
* ``Py_InitializeFromConfig(config)``
* ``Py_PreInitialize(preconfig)``
* ``Py_PreInitializeFromArgs(preconfig, argc, argv)``
* ``Py_PreInitializeFromBytesArgs(preconfig, argc, argv)``
* ``Py_RunMain()``

This PEP also adds ``_PyRuntimeState.preconfig`` (``PyPreConfig`` type)
and ``PyInterpreterState.config`` (``PyConfig`` type) fields to these
internal structures. ``PyInterpreterState.config`` becomes the new
reference configuration, replacing global configuration variables and
other private variables.


``PyWideStringList`` is a list of ``wchar_t*`` strings.

``PyWideStringList`` structure fields:

* ``length`` (``Py_ssize_t``)
* ``items`` (``wchar_t**``)


* ``PyInitError PyWideStringList_Append(PyWideStringList *list, const
wchar_t *item)``:
  Append *item* to *list*.
* ``PyInitError PyWideStringList_Insert(PyWideStringList *list,
Py_ssize_t index, const wchar_t *item)``:
  Insert *item* into *list* at *index*. If *index* is greater than
  *list* length, just append *item* to *list*.

If *length* is non-zero, *items* must be non-NULL and all strings must
be non-NULL.


``PyInitError`` is a structure to store an error message or an exit code
for the Python Initialization. For an error, it stores the C function
name which created the error.


    PyInitError alloc(void **ptr, size_t size)
        *ptr = PyMem_RawMalloc(size);
        if (*ptr == NULL) {
            return PyInitError_NoMemory();
        return PyInitError_Ok();

    int main(int argc, char **argv)
        void *ptr;
        PyInitError err = alloc(&ptr, 16);
        if (PyInitError_Failed(err)) {
        return 0;

``PyInitError`` fields:

* ``exitcode`` (``int``):
  Argument passed to ``exit()``.
* ``err_msg`` (``const char*``):
  Error message.
* ``func`` (``const char *``):
  Name of the function which created an error, can be ``NULL``.
* private ``_type`` field: for internal usage only.

Functions to create an error:

* ``PyInitError_Ok()``: Success.
* ``PyInitError_Error(err_msg)``: Initialization error with a message.
* ``PyInitError_NoMemory()``: Memory allocation failure (out of memory).
* ``PyInitError_Exit(exitcode)``: Exit Python with the specified exit code.

Functions to handle an error:

* ``PyInitError_Failed(err)``: Is the result an error or an exit?
* ``PyInitError_IsError(err)``: Is the result an error?
* ``PyInitError_IsExit(err)``: Is the result an exit?
* ``Py_ExitInitError(err)``: Call ``exit(exitcode)`` if *err* is an
  exit, print the error and exit if *err* is an error. Must only be
  called with an error and an exit: if ``PyInitError_Failed(err)`` is

Preinitialization with PyPreConfig

The ``PyPreConfig`` structure is used to preinitialize Python:

* Set the Python memory allocator
* Configure the LC_CTYPE locale
* Set the UTF-8 mode

Example using the preinitialization to enable the UTF-8 Mode::

    PyPreConfig preconfig;

    preconfig.utf8_mode = 1;

    PyInitError err = Py_PreInitialize(&preconfig);
    if (PyInitError_Failed(err)) {

    /* at this point, Python will speak UTF-8 */

    /* ... use Python API here ... */

Function to initialize a pre-configuration:

* ``void PyPreConfig_InitIsolatedConfig(PyPreConfig *preconfig)``
* ``void PyPreConfig_InitPythonConfig(PyPreConfig *preconfig)``

Functions to preinitialization Python:

* ``PyInitError Py_PreInitialize(const PyPreConfig *preconfig)``
* ``PyInitError Py_PreInitializeFromBytesArgs(const PyPreConfig
*preconfig, int argc, char * const *argv)``
* ``PyInitError Py_PreInitializeFromArgs(const PyPreConfig *preconfig,
int argc, wchar_t * const * argv)``

The caller is responsible to handle error or exit using
``PyInitError_Failed()`` and ``Py_ExitInitError()``.

If Python is initialized with command line arguments, the command line
arguments must also be passed to preinitialize Python, since they have
an effect on the pre-configuration like encodings. For example, the
``-X utf8`` command line option enables the UTF-8 Mode.

``PyPreConfig`` fields:

* ``allocator`` (``int``):
  Name of the memory allocator (ex: ``PYMEM_ALLOCATOR_MALLOC``). Valid

  * ``PYMEM_ALLOCATOR_NOT_SET`` (``0``): don't change memory allocators
    (use defaults)
  * ``PYMEM_ALLOCATOR_DEFAULT`` (``1``): default memory allocators
  * ``PYMEM_ALLOCATOR_DEBUG`` (``2``): enable debug hooks
  * ``PYMEM_ALLOCATOR_MALLOC`` (``3``): force usage of ``malloc()``
  * ``PYMEM_ALLOCATOR_MALLOC_DEBUG`` (``4``): ``malloc()`` with debug hooks
  * ``PYMEM_ALLOCATOR_PYMALLOC`` (``5``): Python "pymalloc" allocator
  * ``PYMEM_ALLOCATOR_PYMALLOC_DEBUG`` (``6``): pymalloc with debug hooks
    ``PYMEM_ALLOCATOR_PYMALLOC_DEBUG`` are not supported if Python is
    configured using ``--without-pymalloc``

* ``configure_locale`` (``int``):
  Set the LC_CTYPE locale to the user preferred locale? If equals to 0,
  set ``coerce_c_locale`` and ``coerce_c_locale_warn`` to 0.
* ``coerce_c_locale`` (``int``):
  If equals to 2, coerce the C locale; if equals to 1, read the LC_CTYPE
  locale to decide if it should be coerced.
* ``coerce_c_locale_warn`` (``int``):
  If non-zero, emit a warning if the C locale is coerced.
* ``dev_mode`` (``int``):
  See ``PyConfig.dev_mode``.
* ``isolated`` (``int``):
  See ``PyConfig.isolated``.
* ``legacy_windows_fs_encoding`` (``int``):
  If non-zero, disable UTF-8 Mode, set the Python filesystem encoding to
  ``mbcs``, set the filesystem error handler to ``replace``.
* ``parse_argv`` (``int``):
  If non-zero, ``Py_PreInitializeFromArgs()`` and
  ``Py_PreInitializeFromBytesArgs()`` parse their ``argv`` argument the
  same way the regular Python parses command line arguments: see
  `Command Line Arguments`_.
* ``use_environment`` (``int``):
  See ``PyConfig.use_environment``.
* ``utf8_mode`` (``int``):
  If non-zero, enable the UTF-8 mode.

The ``legacy_windows_fs_encoding`` is only available on Windows.

There is also a private field, for internal use only,
``_config_version`` (``int``): the configuration version, used
for ABI compatibility.

``PyMem_SetAllocator()`` can be called after ``Py_PreInitialize()`` and
before ``Py_InitializeFromConfig()`` to install a custom memory
allocator. It can be called before ``Py_PreInitialize()`` if
``allocator`` is set to ``PYMEM_ALLOCATOR_NOT_SET`` (default value).

Python memory allocation functions like ``PyMem_RawMalloc()`` must not
be used before Python preinitialization, whereas calling directly
``malloc()`` and ``free()`` is always safe. ``Py_DecodeLocale()`` must
not be called before the preinitialization.

Initialization with PyConfig

The ``PyConfig`` structure contains most parameters to configure Python.

Example setting the program name::

    void init_python(void)
        PyInitError err;
        PyConfig config;

        err = PyConfig_InitPythonConfig(&config);
        if (PyInitError_Failed(err)) {
            goto fail;

        /* Set the program name. Implicitly preinitialize Python. */
        err = PyConfig_SetString(&config, &config.program_name,
        if (PyInitError_Failed(err)) {
            goto fail;

        err = Py_InitializeFromConfig(&config);
        if (PyInitError_Failed(err)) {
            goto fail;


``PyConfig`` methods:

* ``PyInitError PyConfig_InitPythonConfig(PyConfig *config)``
  Initialize configuration with `Python Configuration`_.
* ``PyInitError PyConfig_InitIsolatedConfig(PyConfig *config)``:
  Initialize configuration with `Isolated Configuration`_.
* ``PyInitError PyConfig_SetString(PyConfig *config, wchar_t * const
*config_str, const wchar_t *str)``:
  Copy the wide character string *str* into ``*config_str``.
  Preinitialize Python if needed.
* ``PyInitError PyConfig_SetBytesString(PyConfig *config, wchar_t *
const *config_str, const char *str)``:
  Decode *str* using ``Py_DecodeLocale()`` and set the result into
  Preinitialize Python if needed.
* ``PyInitError PyConfig_SetArgv(PyConfig *config, int argc, wchar_t *
const *argv)``:
  Set command line arguments from wide character strings.
  Preinitialize Python if needed.
* ``PyInitError PyConfig_SetBytesArgv(PyConfig *config, int argc, char
* const *argv)``:
  Set command line arguments: decode bytes using ``Py_DecodeLocale()``.
  Preinitialize Python if needed.
* ``PyInitError PyConfig_Read(PyConfig *config)``:
  Read all Python configuration. Fields which are already initialized
  are left unchanged.
  Preinitialize Python if needed.
* ``void PyConfig_Clear(PyConfig *config)``:
  Release configuration memory.

Most ``PyConfig`` methods preinitialize Python if needed. In that case,
the Python preinitialization configuration in based on the ``PyConfig``.
If configuration fields which are in common with ``PyPreConfig`` are
tuned, they must be set before calling a ``PyConfig`` method:

* ``dev_mode``
* ``isolated``
* ``parse_argv``
* ``use_environment``

Moreover, if ``PyConfig_SetArgv()`` or ``PyConfig_SetBytesArgv()`` is
used, this method must be called first, before other methods, since the
preinitialization configuration depends on command line arguments (if
``parse_argv`` is non-zero).

Functions to initialize Python:

* ``PyInitError Py_InitializeFromConfig(const PyConfig *config)``:
  Initialize Python from *config* configuration.

The caller of these methods and functions is responsible to handle error
or exit using ``PyInitError_Failed()`` and ``Py_ExitInitError()``.

``PyConfig`` fields:

* ``argv`` (``PyWideStringList``):
  Command line arguments, ``sys.argv``. See ``parse_argv`` to parse
  ``argv`` the same way the regular Python parses Python command line
  arguments. If ``argv`` is empty, an empty string is added to ensure
  that ``sys.argv`` always exists and is never empty.
* ``base_exec_prefix`` (``wchar_t*``):
* ``base_prefix`` (``wchar_t*``):
* ``buffered_stdio`` (``int``):
  If equals to 0, enable unbuffered mode, making the stdout and stderr streams
* ``bytes_warning`` (``int``):
  If equals to 1, issue a warning when comparing ``bytes`` or
  ``bytearray`` with ``str``, or comparing ``bytes`` with ``int``. If
  equal or greater to 2, raise a ``BytesWarning`` exception.
* ``check_hash_pycs_mode`` (``wchar_t*``):
  ``--check-hash-based-pycs`` command line option value (see PEP 552).
* ``configure_c_stdio`` (``int``):
  If non-zero, configure C standard streams (``stdio``, ``stdout``,
  ``stdout``).  For example, set their mode to ``O_BINARY`` on Windows.
* ``dev_mode`` (``int``):
  Development mode
* ``dump_refs`` (``int``):
  If non-zero, dump all objects which are still alive at exit
* ``exec_prefix`` (``wchar_t*``):
* ``executable`` (``wchar_t*``):
* ``faulthandler`` (``int``):
  If non-zero, call ``faulthandler.enable()``.
* ``filesystem_encoding`` (``wchar_t*``):
  Filesystem encoding, ``sys.getfilesystemencoding()``.
* ``filesystem_errors`` (``wchar_t*``):
  Filesystem encoding errors, ``sys.getfilesystemencodeerrors()``.
* ``use_hash_seed`` (``int``),
  ``hash_seed`` (``unsigned long``):
  Randomized hash function seed.
* ``home`` (``wchar_t*``):
  Python home directory.
* ``import_time`` (``int``):
  If non-zero, profile import time.
* ``inspect`` (``int``):
  Enter interactive mode after executing a script or a command.
* ``install_signal_handlers`` (``int``):
  Install signal handlers?
* ``interactive`` (``int``):
  Interactive mode.
* ``legacy_windows_stdio`` (``int``, Windows only):
  If non-zero, use ``io.FileIO`` instead of ``WindowsConsoleIO`` for
  ``sys.stdin``, ``sys.stdout`` and ``sys.stderr``.
* ``malloc_stats`` (``int``):
  If non-zero, dump memory allocation statistics at exit.
* ``pythonpath_env`` (``wchar_t*``):
  Module search paths as a string separated by DELIM (usually ``:``).
  Initialized from ``PYTHONPATH`` environment variable value by default.
* ``module_search_paths_set`` (``int``),
  ``module_search_paths`` (``PyWideStringList``):
  ``sys.path``. If ``module_search_paths_set`` is equal to 0, the
  ``module_search_paths`` is replaced by the function computing the
  `Path Configuration`.
* ``optimization_level`` (``int``):
  Compilation optimization level.
* ``parse_argv`` (``int``):
  If non-zero, parse ``argv`` the same way the regular Python command
  line arguments, and strip Python arguments from ``argv``: see `Command
  Line Arguments`_.
* ``parser_debug`` (``int``):
  If non-zero, turn on parser debugging output (for expert only,
  depending on compilation options).
* ``pathconfig_warnings`` (``int``):
  If equal to 0, suppress warnings when computing the path
  configuration (Unix only, Windows does not log any warning). Otherwise,
  warnings are written into stderr.
* ``prefix`` (``wchar_t*``):
* ``program_name`` (``wchar_t*``):
  Program name.
* ``pycache_prefix`` (``wchar_t*``):
  ``.pyc`` cache prefix.
* ``quiet`` (``int``):
  Quiet mode. For example, don't display the copyright and version
  messages even in interactive mode.
* ``run_command`` (``wchar_t*``):
  ``-c COMMAND`` argument.
* ``run_filename`` (``wchar_t*``):
  ``python3 SCRIPT`` argument.
* ``run_module`` (``wchar_t*``):
  ``python3 -m MODULE`` argument.
* ``show_alloc_count`` (``int``):
  Show allocation counts at exit?
* ``show_ref_count`` (``int``):
  Show total reference count at exit?
* ``site_import`` (``int``):
  Import the ``site`` module at startup?
* ``skip_source_first_line`` (``int``):
  Skip the first line of the source?
* ``stdio_encoding`` (``wchar_t*``),
  ``stdio_errors`` (``wchar_t*``):
  Encoding and encoding errors of ``sys.stdin``, ``sys.stdout``
  and ``sys.stderr``.
* ``tracemalloc`` (``int``):
  If non-zero, call ``tracemalloc.start(value)``.
* ``user_site_directory`` (``int``):
  If non-zero, add user site directory to ``sys.path``.
* ``verbose`` (``int``):
  If non-zero, enable verbose mode.
* ``warnoptions`` (``PyWideStringList``):
  Options of the ``warnings`` module to build warnings filters.
* ``write_bytecode`` (``int``):
  If non-zero, write ``.pyc`` files.
* ``xoptions`` (``PyWideStringList``):

If ``parse_argv`` is non-zero, ``argv`` arguments are parsed the same
way the regular Python parses command line arguments, and Python
arguments are stripped from ``argv``: see `Command Line Arguments`_.

The ``xoptions`` options are parsed to set other options: see `-X

``PyConfig`` private fields, for internal use only:

* ``_config_version`` (``int``):
  Configuration version, used for ABI compatibility.
* ``_config_init`` (``int``):
  Function used to initalize ``PyConfig``, used for preinitialization.
* ``_install_importlib`` (``int``):
  Install importlib?
* ``_init_main`` (``int``):
  If equal to 0, stop Python initialization before the "main" phase
  (see PEP 432).

More complete example modifying the default configuration, read the
configuration, and then override some parameters::

    PyInitError init_python(const char *program_name)
        PyInitError err;
        PyConfig config;

        err = PyConfig_InitPythonConfig(&config);
        if (PyInitError_Failed(err)) {
            goto done;

        /* Set the program name before reading the configuraton
           (decode byte string from the locale encoding).

           Implicitly preinitialize Python. */
        err = PyConfig_SetBytesString(&config, &config.program_name,
        if (PyInitError_Failed(err)) {
            goto done;

        /* Read all configuration at once */
        err = PyConfig_Read(&config);
        if (PyInitError_Failed(err)) {
            goto done;

        /* Append our custom search path to sys.path */
        err = PyWideStringList_Append(&config.module_search_paths,
        if (PyInitError_Failed(err)) {
            goto done;

        /* Override executable computed by PyConfig_Read() */
        err = PyConfig_SetString(&config, &config.executable,
        if (PyInitError_Failed(err)) {
            goto done;

        err = Py_InitializeFromConfig(&config);

        return err;

.. note::
   ``PyImport_FrozenModules``, ``PyImport_AppendInittab()`` and
   ``PyImport_ExtendInittab()`` functions are still relevant and
   continue to work as previously. They should be set or called
   before the Python initialization.

Isolated Configuration

``PyPreConfig_InitIsolatedConfig()`` and
``PyConfig_InitIsolatedConfig()`` functions create a configuration to
isolate Python from the system. For example, to embed Python into an

This configuration ignores global configuration variables, environments
variables and command line arguments (``argv`` is not parsed). The C
standard streams (ex: ``stdout``) and the LC_CTYPE locale are left
unchanged by default.

Configuration files are still used with this configuration. Set the
`Path Configuration`_ ("output fields") to ignore these configuration
files and avoid the function computing the default path configuration.

Python Configuration

``PyPreConfig_InitPythonConfig()`` and ``PyConfig_InitPythonConfig()``
functions create a configuration to build a customized Python which
behaves as the regular Python.

Environments variables and command line arguments are used to configure
Python, whereas global configuration variables are ignored.

This function enables C locale coercion (PEP 538) and UTF-8 Mode (PEP
540) depending on the LC_CTYPE locale, ``PYTHONUTF8`` and
``PYTHONCOERCECLOCALE`` environment variables.

Example of customized Python always running in isolated mode::

    int main(int argc, char **argv)
        PyConfig config;
        PyInitError err;

        err = PyConfig_InitPythonConfig(&config);
        if (PyInitError_Failed(err)) {
            goto fail;

        config.isolated = 1;

        /* Decode command line arguments.
           Implicitly preinitialize Python (in isolated mode). */
        err = PyConfig_SetBytesArgv(&config, argc, argv);
        if (PyInitError_Failed(err)) {
            goto fail;

        err = Py_InitializeFromConfig(&config);
        if (PyInitError_Failed(err)) {
            goto fail;

        return Py_RunMain();

        if (!PyInitError_IsExit(err)) {
            /* Display the error message and exit the process with
               non-zero exit code */
        return err.exitcode;

This example is a basic implementation of the "System Python Executable"
discussed in PEP 432.

Path Configuration

``PyConfig`` contains multiple fields for the path configuration:

* Path configuration input fields:

  * ``home``
  * ``pythonpath_env``
  * ``pathconfig_warnings``

* Path configuration output fields:

  * ``exec_prefix``
  * ``executable``
  * ``prefix``
  * ``module_search_paths_set``, ``module_search_paths``

It is possible to completely ignore the function computing the default
path configuration by setting explicitly all path configuration output
fields listed above. A string is considered as set even if it's an empty
string. ``module_search_paths`` is considered as set if
``module_search_paths_set`` is set to 1. In this case, path
configuration input fields are ignored as well.

Set ``pathconfig_warnings`` to 0 to suppress warnings when computing the
path configuration (Unix only, Windows does not log any warning).

If ``base_prefix`` or ``base_exec_prefix`` fields are not set, they
inherit their value from ``prefix`` and ``exec_prefix`` respectively.

If ``site_import`` is non-zero, ``sys.path`` can be modified by the
``site`` module. For example, if ``user_site_directory`` is non-zero,
the user site directory is added to ``sys.path`` (if it exists).

See also `Configuration Files`_ used by the path configuration.


Python 3.7 provides a high-level ``Py_Main()`` function which requires
to pass command line arguments as ``wchar_t*`` strings. It is
non-trivial to use the correct encoding to decode bytes. Python has its
own set of issues with C locale coercion and UTF-8 Mode.

This PEP adds a new ``Py_BytesMain()`` function which takes command line
arguments as bytes::

    int Py_BytesMain(int argc, char **argv)


The new ``Py_RunMain()`` function executes the command
(``PyConfig.run_command``), the script (``PyConfig.run_filename``) or
the module (``PyConfig.run_module``) specified on the command line or in
the configuration, and then finalizes Python. It returns an exit status
that can be passed to the ``exit()`` function. ::

    int Py_RunMain(void);

See `Python Configuration`_ for an example of customized Python always
running in isolated mode using ``Py_RunMain()``.

Backwards Compatibility

This PEP only adds a new API: it leaves the existing API unchanged and
has no impact on the backwards compatibility.

The Python 3.7 ``Py_Initialize()`` function now disable the C locale
coercion (PEP 538) and the UTF-8 Mode (PEP 540) by default to prevent
mojibake. The new API using the `Python Configuration`_ is needed to
enable them automatically.


Comparison of Python and Isolated Configurations

Differences between ``PyPreConfig_InitPythonConfig()``
and ``PyPreConfig_InitIsolatedConfig()``:

===============================  =======  ========
PyPreConfig                      Python   Isolated
===============================  =======  ========
``coerce_c_locale_warn``              -1         0
``coerce_c_locale``                   -1         0
``configure_locale``               **1**         0
``dev_mode``                          -1         0
``isolated``                          -1     **1**
``legacy_windows_fs_encoding``        -1         0
``use_environment``                   -1         0
``parse_argv``                     **1**         0
``utf8_mode``                         -1         0
===============================  =======  ========

Differences between ``PyConfig_InitPythonConfig()``
and ``PyConfig_InitIsolatedConfig()``:

===============================  =======  ========
PyConfig                         Python   Isolated
===============================  =======  ========
``configure_c_stdio``              **1**         0
``install_signal_handlers``        **1**         0
``isolated``                           0     **1**
``parse_argv``                     **1**         0
``pathconfig_warnings``            **1**         0
``use_environment``                **1**         0
``user_site_directory``            **1**         0
===============================  =======  ========

Priority and Rules

Priority of configuration parameters, highest to lowest:

* ``PyConfig``
* ``PyPreConfig``
* Configuration files
* Command line options
* Environment variables
* Global configuration variables

Priority of warning options, highest to lowest:

* ``PyConfig.warnoptions``
* ``PyConfig.dev_mode`` (add ``"default"``)
* ``PYTHONWARNINGS`` environment variables
* ``-W WARNOPTION`` command line argument
* ``PyConfig.bytes_warning`` (add ``"error::BytesWarning"`` if greater
  than 1, or add ``"default::BytesWarning``)

Rules on ``PyConfig`` parameters:

* If ``isolated`` is non-zero, ``use_environment`` and
  ``user_site_directory`` are set to 0.
* If ``dev_mode`` is non-zero, ``allocator`` is set to ``"debug"``,
  ``faulthandler`` is set to 1, and ``"default"`` filter is added to
  ``warnoptions``. But the ``PYTHONMALLOC`` environment variable has the
  priority over ``dev_mode`` to set the memory allocator.
* If ``base_prefix`` is not set, it inherits ``prefix`` value.
* If ``base_exec_prefix`` is not set, it inherits ``exec_prefix`` value.
* If the ``python._pth`` configuration file is present, ``isolated`` is
  set to 1 and ``site_import`` is set to 0; but ``site_import`` is set
  to 1 if ``python._pth`` contains ``import site``.

Rules on ``PyConfig`` and ``PyPreConfig`` parameters:

* If ``PyPreConfig.legacy_windows_fs_encoding`` is non-zero,
  set ``PyPreConfig.utf8_mode`` to 0, set
  ``PyConfig.filesystem_encoding`` to ``mbcs``, and set
  ``PyConfig.filesystem_errors`` to ``replace``.

Configuration Files

Python configuration files used by the `Path Configuration`_:

* ``pyvenv.cfg``
* ``python._pth`` (Windows only)
* ``pybuilddir.txt`` (Unix only)

Global Configuration Variables

Global configuration variables mapped to ``PyPreConfig`` fields:

========================================  ================================
Variable                                  Field
========================================  ================================
``Py_IgnoreEnvironmentFlag``              ``use_environment`` (NOT)
``Py_IsolatedFlag``                       ``isolated``
``Py_LegacyWindowsFSEncodingFlag``        ``legacy_windows_fs_encoding``
``Py_UTF8Mode``                           ``utf8_mode``
========================================  ================================

(NOT) means that the ``PyPreConfig`` value is the oposite of the global
configuration variable value. ``Py_LegacyWindowsFSEncodingFlag`` is only
available on Windows.

Global configuration variables mapped to ``PyConfig`` fields:

========================================  ================================
Variable                                  Field
========================================  ================================
``Py_BytesWarningFlag``                   ``bytes_warning``
``Py_DebugFlag``                          ``parser_debug``
``Py_DontWriteBytecodeFlag``              ``write_bytecode`` (NOT)
``Py_FileSystemDefaultEncodeErrors``      ``filesystem_errors``
``Py_FileSystemDefaultEncoding``          ``filesystem_encoding``
``Py_FrozenFlag``                         ``pathconfig_warnings`` (NOT)
``Py_HasFileSystemDefaultEncoding``       ``filesystem_encoding``
``Py_HashRandomizationFlag``              ``use_hash_seed``, ``hash_seed``
``Py_IgnoreEnvironmentFlag``              ``use_environment`` (NOT)
``Py_InspectFlag``                        ``inspect``
``Py_InteractiveFlag``                    ``interactive``
``Py_IsolatedFlag``                       ``isolated``
``Py_LegacyWindowsStdioFlag``             ``legacy_windows_stdio``
``Py_NoSiteFlag``                         ``site_import`` (NOT)
``Py_NoUserSiteDirectory``                ``user_site_directory`` (NOT)
``Py_OptimizeFlag``                       ``optimization_level``
``Py_QuietFlag``                          ``quiet``
``Py_UnbufferedStdioFlag``                ``buffered_stdio`` (NOT)
``Py_VerboseFlag``                        ``verbose``
``_Py_HasFileSystemDefaultEncodeErrors``  ``filesystem_errors``
========================================  ================================

(NOT) means that the ``PyConfig`` value is the oposite of the global
configuration variable value. ``Py_LegacyWindowsStdioFlag`` is only
available on Windows.

Command Line Arguments


    python3 [options]
    python3 [options] -c COMMAND
    python3 [options] -m MODULE
    python3 [options] SCRIPT

Command line options mapped to pseudo-action on ``PyPreConfig`` fields:

================================  ================================
Option                            ``PyConfig`` field
================================  ================================
``-E``                            ``use_environment = 0``
``-I``                            ``isolated = 1``
``-X dev``                        ``dev_mode = 1``
``-X utf8``                       ``utf8_mode = 1``
``-X utf8=VALUE``                 ``utf8_mode = VALUE``
================================  ================================

Command line options mapped to pseudo-action on ``PyConfig`` fields:

================================  ================================
Option                            ``PyConfig`` field
================================  ================================
``-b``                            ``bytes_warning++``
``-B``                            ``write_bytecode = 0``
``-c COMMAND``                    ``run_command = COMMAND``
``--check-hash-based-pycs=MODE``  ``_check_hash_pycs_mode = MODE``
``-d``                            ``parser_debug++``
``-E``                            ``use_environment = 0``
``-i``                            ``inspect++`` and ``interactive++``
``-I``                            ``isolated = 1``
``-m MODULE``                     ``run_module = MODULE``
``-O``                            ``optimization_level++``
``-q``                            ``quiet++``
``-R``                            ``use_hash_seed = 0``
``-s``                            ``user_site_directory = 0``
``-S``                            ``site_import``
``-t``                            ignored (kept for backwards compatibility)
``-u``                            ``buffered_stdio = 0``
``-v``                            ``verbose++``
``-W WARNING``                    add ``WARNING`` to ``warnoptions``
``-x``                            ``skip_source_first_line = 1``
``-X OPTION``                     add ``OPTION`` to ``xoptions``
================================  ================================

``-h``, ``-?`` and ``-V`` options are handled without ``PyConfig``.

-X Options

-X options mapped to pseudo-action on ``PyConfig`` fields:

================================  ================================
Option                            ``PyConfig`` field
================================  ================================
``-X dev``                        ``dev_mode = 1``
``-X faulthandler``               ``faulthandler = 1``
``-X importtime``                 ``import_time = 1``
``-X pycache_prefix=PREFIX``      ``pycache_prefix = PREFIX``
``-X showalloccount``             ``show_alloc_count = 1``
``-X showrefcount``               ``show_ref_count = 1``
``-X tracemalloc=N``              ``tracemalloc = N``
================================  ================================

Environment Variables

Environment variables mapped to ``PyPreConfig`` fields:

=================================  =============================================
Variable                           ``PyPreConfig`` field
=================================  =============================================
``PYTHONCOERCECLOCALE``            ``coerce_c_locale``, ``coerce_c_locale_warn``
``PYTHONDEVMODE``                  ``dev_mode``
``PYTHONLEGACYWINDOWSFSENCODING``  ``legacy_windows_fs_encoding``
``PYTHONMALLOC``                   ``allocator``
``PYTHONUTF8``                     ``utf8_mode``
=================================  =============================================

Environment variables mapped to ``PyConfig`` fields:

=================================  ====================================
Variable                           ``PyConfig`` field
=================================  ====================================
``PYTHONDEBUG``                    ``parser_debug``
``PYTHONDEVMODE``                  ``dev_mode``
``PYTHONDONTWRITEBYTECODE``        ``write_bytecode``
``PYTHONDUMPREFS``                 ``dump_refs``
``PYTHONEXECUTABLE``               ``program_name``
``PYTHONFAULTHANDLER``             ``faulthandler``
``PYTHONHASHSEED``                 ``use_hash_seed``, ``hash_seed``
``PYTHONHOME``                     ``home``
``PYTHONINSPECT``                  ``inspect``
``PYTHONIOENCODING``               ``stdio_encoding``, ``stdio_errors``
``PYTHONLEGACYWINDOWSSTDIO``       ``legacy_windows_stdio``
``PYTHONMALLOCSTATS``              ``malloc_stats``
``PYTHONNOUSERSITE``               ``user_site_directory``
``PYTHONOPTIMIZE``                 ``optimization_level``
``PYTHONPATH``                     ``pythonpath_env``
``PYTHONPROFILEIMPORTTIME``        ``import_time``
``PYTHONPYCACHEPREFIX,``           ``pycache_prefix``
``PYTHONTRACEMALLOC``              ``tracemalloc``
``PYTHONUNBUFFERED``               ``buffered_stdio``
``PYTHONVERBOSE``                  ``verbose``
``PYTHONWARNINGS``                 ``warnoptions``
=================================  ====================================

specific to Windows.

Default Python Configugration


* ``allocator`` = ``PYMEM_ALLOCATOR_NOT_SET``
* ``coerce_c_locale_warn`` = -1
* ``coerce_c_locale`` = -1
* ``configure_locale`` = 1
* ``dev_mode`` = -1
* ``isolated`` = -1
* ``legacy_windows_fs_encoding`` = -1
* ``use_environment`` = -1
* ``utf8_mode`` = -1


* ``argv`` = []
* ``base_exec_prefix`` = ``NULL``
* ``base_prefix`` = ``NULL``
* ``buffered_stdio`` = 1
* ``bytes_warning`` = 0
* ``check_hash_pycs_mode`` = ``NULL``
* ``configure_c_stdio`` = 1
* ``dev_mode`` = 0
* ``dump_refs`` = 0
* ``exec_prefix`` = ``NULL``
* ``executable`` = ``NULL``
* ``faulthandler`` = 0
* ``filesystem_encoding`` = ``NULL``
* ``filesystem_errors`` = ``NULL``
* ``hash_seed`` = 0
* ``home`` = ``NULL``
* ``import_time`` = 0
* ``inspect`` = 0
* ``install_signal_handlers`` = 1
* ``interactive`` = 0
* ``isolated`` = 0
* ``malloc_stats`` = 0
* ``module_search_path_env`` = ``NULL``
* ``module_search_paths`` = []
* ``optimization_level`` = 0
* ``parse_argv`` = 1
* ``parser_debug`` = 0
* ``pathconfig_warnings`` = 1
* ``prefix`` = ``NULL``
* ``program_name`` = ``NULL``
* ``pycache_prefix`` = ``NULL``
* ``quiet`` = 0
* ``run_command`` = ``NULL``
* ``run_filename`` = ``NULL``
* ``run_module`` = ``NULL``
* ``show_alloc_count`` = 0
* ``show_ref_count`` = 0
* ``site_import`` = 1
* ``skip_source_first_line`` = 0
* ``stdio_encoding`` = ``NULL``
* ``stdio_errors`` = ``NULL``
* ``tracemalloc`` = 0
* ``use_environment`` = 1
* ``use_hash_seed`` = 0
* ``user_site_directory`` = 1
* ``verbose`` = 0
* ``warnoptions`` = []
* ``write_bytecode`` = 1
* ``xoptions`` = []
* ``_init_main`` = 1
* ``_install_importlib`` = 1

Default Isolated Configugration


* ``allocator`` = ``PYMEM_ALLOCATOR_NOT_SET``
* ``coerce_c_locale_warn`` = 0
* ``coerce_c_locale`` = 0
* ``configure_locale`` = 0
* ``dev_mode`` = 0
* ``isolated`` = 1
* ``legacy_windows_fs_encoding`` = 0
* ``use_environment`` = 0
* ``utf8_mode`` = 0


* ``argv`` = []
* ``base_exec_prefix`` = ``NULL``
* ``base_prefix`` = ``NULL``
* ``buffered_stdio`` = 1
* ``bytes_warning`` = 0
* ``check_hash_pycs_mode`` = ``NULL``
* ``configure_c_stdio`` = 0
* ``dev_mode`` = 0
* ``dump_refs`` = 0
* ``exec_prefix`` = ``NULL``
* ``executable`` = ``NULL``
* ``faulthandler`` = 0
* ``filesystem_encoding`` = ``NULL``
* ``filesystem_errors`` = ``NULL``
* ``hash_seed`` = 0
* ``home`` = ``NULL``
* ``import_time`` = 0
* ``inspect`` = 0
* ``install_signal_handlers`` = 0
* ``interactive`` = 0
* ``isolated`` = 1
* ``malloc_stats`` = 0
* ``module_search_path_env`` = ``NULL``
* ``module_search_paths`` = []
* ``optimization_level`` = 0
* ``parse_argv`` = 0
* ``parser_debug`` = 0
* ``pathconfig_warnings`` = 0
* ``prefix`` = ``NULL``
* ``program_name`` = ``NULL``
* ``pycache_prefix`` = ``NULL``
* ``quiet`` = 0
* ``run_command`` = ``NULL``
* ``run_filename`` = ``NULL``
* ``run_module`` = ``NULL``
* ``show_alloc_count`` = 0
* ``show_ref_count`` = 0
* ``site_import`` = 1
* ``skip_source_first_line`` = 0
* ``stdio_encoding`` = ``NULL``
* ``stdio_errors`` = ``NULL``
* ``tracemalloc`` = 0
* ``use_environment`` = 0
* ``use_hash_seed`` = 0
* ``user_site_directory`` = 0
* ``verbose`` = 0
* ``warnoptions`` = []
* ``write_bytecode`` = 1
* ``xoptions`` = []
* ``_init_main`` = 1
* ``_install_importlib`` = 1

Python 3.7 API

Python 3.7 has 4 functions in its C API to initialize and finalize

* ``Py_Initialize()``, ``Py_InitializeEx()``: initialize Python
* ``Py_Finalize()``, ``Py_FinalizeEx()``: finalize Python

Python 3.7 can be configured using `Global Configuration Variables`_,
`Environment Variables`_, and the following functions:

* ``PyImport_AppendInittab()``
* ``PyImport_ExtendInittab()``
* ``PyMem_SetAllocator()``
* ``PyMem_SetupDebugHooks()``
* ``PyObject_SetArenaAllocator()``
* ``Py_SetPath()``
* ``Py_SetProgramName()``
* ``Py_SetPythonHome()``
* ``Py_SetStandardStreamEncoding()``
* ``PySys_AddWarnOption()``
* ``PySys_AddXOption()``
* ``PySys_ResetWarnOptions()``

There is also a high-level ``Py_Main()`` function and
``PyImport_FrozenModules`` variable which can be overridden.

See `Initialization, Finalization, and Threads
<https://docs.python.org/dev/c-api/init.html>`_ documentation.

Python Issues

Issues that will be fixed by this PEP, directly or indirectly:

* `bpo-1195571 <https://bugs.python.org/issue1195571>`_: "simple
  callback system for Py_FatalError"
* `bpo-11320 <https://bugs.python.org/issue11320>`_:
  "Usage of API method Py_SetPath causes errors in Py_Initialize()
  (Posix ony)"
* `bpo-13533 <https://bugs.python.org/issue13533>`_: "Would like
  Py_Initialize to play friendly with host app"
* `bpo-14956 <https://bugs.python.org/issue14956>`_: "custom PYTHONPATH
  may break apps embedding Python"
* `bpo-19983 <https://bugs.python.org/issue19983>`_: "When interrupted
  during startup, Python should not call abort() but exit()"
* `bpo-22213 <https://bugs.python.org/issue22213>`_: "Make pyvenv style
  virtual environments easier to configure when embedding Python". This
  PEP more or
* `bpo-22257 <https://bugs.python.org/issue22257>`_: "PEP 432: Redesign
  the interpreter startup sequence"
* `bpo-29778 <https://bugs.python.org/issue29778>`_: "_Py_CheckPython3
  uses uninitialized dllpath when embedder sets module path with
* `bpo-30560 <https://bugs.python.org/issue30560>`_: "Add
  Py_SetFatalErrorAbortFunc: Allow embedding program to handle fatal
* `bpo-31745 <https://bugs.python.org/issue31745>`_: "Overloading
  "Py_GetPath" does not work"
* `bpo-32573 <https://bugs.python.org/issue32573>`_: "All sys attributes
  (.argv, ...) should exist in embedded environments".
* `bpo-34725 <https://bugs.python.org/issue34725>`_:
  "Py_GetProgramFullPath() odd behaviour in Windows"
* `bpo-36204 <https://bugs.python.org/issue36204>`_: "Deprecate calling
  Py_Main() after Py_Initialize()? Add Py_InitializeFromArgv()?"
* `bpo-33135 <https://bugs.python.org/issue33135>`_: "Define field
  prefixes for the various config structs". The PEP now defines well
  how warnings options are handled.

Issues of the PEP implementation:

* `bpo-16961 <https://bugs.python.org/issue16961>`_: "No regression
  tests for -E and individual environment vars"
* `bpo-20361 <https://bugs.python.org/issue20361>`_: "-W command line
  options and PYTHONWARNINGS environmental variable should not override
  -b / -bb command line options"
* `bpo-26122 <https://bugs.python.org/issue26122>`_: "Isolated mode
  doesn't ignore PYTHONHASHSEED"
* `bpo-29818 <https://bugs.python.org/issue29818>`_:
  "Py_SetStandardStreamEncoding leads to a memory error in debug mode"
* `bpo-31845 <https://bugs.python.org/issue31845>`_:
* `bpo-32030 <https://bugs.python.org/issue32030>`_: "PEP 432: Rewrite
* `bpo-32124 <https://bugs.python.org/issue32124>`_: "Document functions
  safe to be called before Py_Initialize()"
* `bpo-33042 <https://bugs.python.org/issue33042>`_: "New 3.7 startup
  sequence crashes PyInstaller"
* `bpo-33932 <https://bugs.python.org/issue33932>`_: "Calling
  Py_Initialize() twice now triggers a fatal error (Python 3.7)"
* `bpo-34008 <https://bugs.python.org/issue34008>`_: "Do we support
  calling Py_Main() after Py_Initialize()?"
* `bpo-34170 <https://bugs.python.org/issue34170>`_: "Py_Initialize():
  computing path configuration must not have side effect (PEP 432)"
* `bpo-34589 <https://bugs.python.org/issue34589>`_: "Py_Initialize()
  and Py_Main() should not enable C locale coercion"
* `bpo-34639 <https://bugs.python.org/issue34639>`_:
  "PYTHONCOERCECLOCALE is ignored when using -E or -I option"
* `bpo-36142 <https://bugs.python.org/issue36142>`_: "Add a new
  _PyPreConfig step to Python initialization to setup memory allocator
  and encodings"
* `bpo-36202 <https://bugs.python.org/issue36202>`_: "Calling
  Py_DecodeLocale() before _PyPreConfig_Write() can produce mojibake"
* `bpo-36301 <https://bugs.python.org/issue36301>`_: "Add
  _Py_PreInitialize() function"
* `bpo-36443 <https://bugs.python.org/issue36443>`_: "Disable
  coerce_c_locale and utf8_mode by default in _PyPreConfig?"
* `bpo-36444 <https://bugs.python.org/issue36444>`_: "Python
  initialization: remove _PyMainInterpreterConfig"
* `bpo-36471 <https://bugs.python.org/issue36471>`_: "PEP 432, PEP 587:
  Add _Py_RunMain()"
* `bpo-36763 <https://bugs.python.org/issue36763>`_: "PEP 587: Rework
  initialization API to prepare second version of the PEP"
* `bpo-36775 <https://bugs.python.org/issue36775>`_: "Rework filesystem
  codec implementation"
* `bpo-36900 <https://bugs.python.org/issue36900>`_: "Use _PyCoreConfig
  rather than global configuration variables"

Issues related to this PEP:

* `bpo-12598 <https://bugs.python.org/issue12598>`_: "Move sys variable
  initialization from import.c to sysmodule.c"
* `bpo-15577 <https://bugs.python.org/issue15577>`_: "Real argc and argv
  in embedded interpreter"
* `bpo-16202 <https://bugs.python.org/issue16202>`_: "sys.path[0]
  security issues"
* `bpo-18309 <https://bugs.python.org/issue18309>`_: "Make python
  slightly more relocatable"
* `bpo-25631 <https://bugs.python.org/issue25631>`_: "Segmentation fault
  with invalid Unicode command-line arguments in embedded Python"
* `bpo-26007 <https://bugs.python.org/issue26007>`_: "Support embedding
  the standard library in an executable"
* `bpo-31210 <https://bugs.python.org/issue31210>`_: "Can not import
  modules if sys.prefix contains DELIM".
* `bpo-31349 <https://bugs.python.org/issue31349>`_: "Embedded
  initialization ignores Py_SetProgramName()"
* `bpo-33919 <https://bugs.python.org/issue33919>`_: "Expose
  _PyCoreConfig structure to Python"
* `bpo-35173 <https://bugs.python.org/issue35173>`_: "Re-use already
  existing functionality to allow Python 2.7.x (both embedded and
  standalone) to locate the module path according to the shared library"

Version History

* Version 4:

  * Introduce "Python Configuration" and "Isolated Configuration" which
    are well better defined. Replace all macros with functions.
  * Replace ``PyPreConfig_INIT`` and ``PyConfig_INIT`` macros with

    * ``PyPreConfig_InitIsolatedConfig()``, ``PyConfig_InitIsolatedConfig()``
    * ``PyPreConfig_InitPythonConfig()``, ``PyConfig_InitPythonConfig()``

  * ``PyPreConfig`` no longer uses dynamic memory, the ``allocator``
    field type becomes an int, add ``configure_locale`` and
    ``parse_argv`` field.
  * ``PyConfig``: rename ``module_search_path_env`` to
    ``pythonpath_env``, rename ``use_module_search_paths`` to
    ``module_search_paths_set``, remove ``program`` and ``dll_path``.
  * Replace ``Py_INIT_xxx()`` macros with ``PyInitError_xxx()``
  * Remove the "Constant PyConfig" section. Remove
    ``Py_InitializeFromArgs()`` and ``Py_InitializeFromBytesArgs()``

* Version 3:

  * ``PyConfig``: Add ``configure_c_stdio`` and ``parse_argv``;
    rename ``_frozen`` to ``pathconfig_warnings``.
  * Rename functions using bytes strings and wide character strings. For
    example, ``Py_PreInitializeFromWideArgs()`` becomes
    ``Py_PreInitializeFromArgs()``, and ``PyConfig_SetArgv()`` becomes
  * Add ``PyWideStringList_Insert()`` function.
  * New "Path configuration", "Isolate Python", "Python Issues"
    and "Version History" sections.
  * ``PyConfig_SetString()`` and ``PyConfig_SetBytesString()`` now
    requires the configuration as the first argument.
  * Rename ``Py_UnixMain()`` to ``Py_BytesMain()``

* Version 2: Add ``PyConfig`` methods (ex: ``PyConfig_Read()``), add
  ``PyWideStringList_Append()``, rename ``PyWideCharList`` to
* Version 1: Initial version.


This document has been placed in the public domain.

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