python-peps/peps/pep-0587.rst

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

Abstract
========

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
(``sys.path``).

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).


Rationale
=========

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
``sys.executable``.

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

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

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
Rules`_.

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 and functions.

New structures:

* ``PyConfig``
* ``PyPreConfig``
* ``PyStatus``
* ``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)``
* ``PyPreConfig_InitIsolatedConfig(preconfig)``
* ``PyPreConfig_InitPythonConfig(preconfig)``
* ``PyStatus_Error(err_msg)``
* ``PyStatus_Exception(status)``
* ``PyStatus_Exit(exitcode)``
* ``PyStatus_IsError(status)``
* ``PyStatus_IsExit(status)``
* ``PyStatus_NoMemory()``
* ``PyStatus_Ok()``
* ``PyWideStringList_Append(list, item)``
* ``PyWideStringList_Insert(list, index, item)``
* ``Py_BytesMain(argc, argv)``
* ``Py_ExitStatusException(status)``
* ``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
----------------

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

``PyWideStringList`` structure fields:

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

Methods:

* ``PyStatus PyWideStringList_Append(PyWideStringList *list, const wchar_t *item)``:
  Append *item* to *list*.
* ``PyStatus 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.

PyStatus
--------

``PyStatus`` is a structure to store the status of an initialization
function: success, error or exit. For an error, it can store the C
function name which created the error.

Example::

    PyStatus alloc(void **ptr, size_t size)
    {
        *ptr = PyMem_RawMalloc(size);
        if (*ptr == NULL) {
            return PyStatus_NoMemory();
        }
        return PyStatus_Ok();
    }

    int main(int argc, char **argv)
    {
        void *ptr;
        PyStatus status = alloc(&ptr, 16);
        if (PyStatus_Exception(status)) {
            Py_ExitStatusException(status);
        }
        PyMem_Free(ptr);
        return 0;
    }

``PyStatus`` 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 a status:

* ``PyStatus_Ok()``: Success.
* ``PyStatus_Error(err_msg)``: Initialization error with a message.
* ``PyStatus_NoMemory()``: Memory allocation failure (out of memory).
* ``PyStatus_Exit(exitcode)``: Exit Python with the specified exit code.

Functions to handle a status:

* ``PyStatus_Exception(status)``: Is the result an error or an exit?
  If true, the exception must be handled; by calling
  ``Py_ExitStatusException(status)`` for example.
* ``PyStatus_IsError(status)``: Is the result an error?
* ``PyStatus_IsExit(status)``: Is the result an exit?
* ``Py_ExitStatusException(status)``: Call ``exit(exitcode)`` if *status*
  is an exit. Print the error messageand exit with a non-zero exit code
  if *status* is an error.  Must only be called if
  ``PyStatus_Exception(status)`` is true.

.. note::
   Internally, Python uses macros which set ``PyStatus.func``,
   whereas functions to create a status set ``func`` to ``NULL``.


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::

    PyStatus status;
    PyPreConfig preconfig;

    PyPreConfig_InitPythonConfig(&preconfig);

    preconfig.utf8_mode = 1;

    status = Py_PreInitialize(&preconfig);
    if (PyStatus_Exception(status)) {
        Py_ExitStatusException(status);
    }

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

    Py_Initialize();
    /* ... use Python API here ... */
    Py_Finalize();

Function to initialize a preconfiguration:

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

Functions to preinitialize Python:

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

The caller is responsible to handle exceptions (error or exit) using
``PyStatus_Exception()`` and ``Py_ExitStatusException()``.

For `Python Configuration`_ (``PyPreConfig_InitPythonConfig()``),
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
  values:

  * ``PYMEM_ALLOCATOR_NOT_SET`` (``0``): don't change memory allocators
    (use defaults)
  * ``PYMEM_ALLOCATOR_DEFAULT`` (``1``): default memory allocators
  * ``PYMEM_ALLOCATOR_DEBUG`` (``2``): default memory allocators with
    debug hooks
  * ``PYMEM_ALLOCATOR_MALLOC`` (``3``): force usage of ``malloc()``
  * ``PYMEM_ALLOCATOR_MALLOC_DEBUG`` (``4``): force usage of
    ``malloc()`` with debug hooks
  * ``PYMEM_ALLOCATOR_PYMALLOC`` (``5``): Python "pymalloc" allocator
  * ``PYMEM_ALLOCATOR_PYMALLOC_DEBUG`` (``6``): Python "pymalloc"
    allocator with debug hooks
  * Note: ``PYMEM_ALLOCATOR_PYMALLOC`` and
    ``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``, Windows only):
  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`` field is only available on Windows.
``#ifdef MS_WINDOWS`` macro can be used for Windows specific code.

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

* ``_config_init`` (``int``):
  Function used to initialize ``PyConfig``, used for preinitialization.

``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)
    {
        PyStatus status;

        PyConfig config;
        PyConfig_InitPythonConfig(&config);

        /* Set the program name. Implicitly preinitialize Python. */
        status = PyConfig_SetString(&config, &config.program_name,
                                    L"/path/to/my_program");
        if (PyStatus_Exception(status)) {
            goto fail;
        }

        status = Py_InitializeFromConfig(&config);
        if (PyStatus_Exception(status)) {
            goto fail;
        }
        PyConfig_Clear(&config);
        return;

    fail:
        PyConfig_Clear(&config);
        Py_ExitStatusException(status);
    }

``PyConfig`` methods:

* ``void PyConfig_InitPythonConfig(PyConfig *config)``
  Initialize configuration with `Python Configuration`_.
* ``void PyConfig_InitIsolatedConfig(PyConfig *config)``:
  Initialize configuration with `Isolated Configuration`_.
* ``PyStatus 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.
* ``PyStatus PyConfig_SetBytesString(PyConfig *config, wchar_t * const *config_str, const char *str)``:
  Decode *str* using ``Py_DecodeLocale()`` and set the result into
  ``*config_str``.
  Preinitialize Python if needed.
* ``PyStatus PyConfig_SetArgv(PyConfig *config, int argc, wchar_t * const *argv)``:
  Set command line arguments from wide character strings.
  Preinitialize Python if needed.
* ``PyStatus PyConfig_SetBytesArgv(PyConfig *config, int argc, char * const *argv)``:
  Set command line arguments: decode bytes using ``Py_DecodeLocale()``.
  Preinitialize Python if needed.
* ``PyStatus 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:

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

The caller of these methods and functions is responsible to handle
exceptions (error or exit) using ``PyStatus_Exception()`` and
``Py_ExitStatusException()``.


``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*``):
  ``sys.base_exec_prefix``.
* ``base_prefix`` (``wchar_t*``):
  ``sys.base_prefix``.
* ``buffered_stdio`` (``int``):
  If equals to 0, enable unbuffered mode, making the stdout and stderr streams
  unbuffered.
* ``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`).
  Valid values: ``always``, ``never`` and ``default``. The default value
  is ``default``.
* ``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.
  Require a special Python build with ``Py_REF_DEBUG`` macro defined.
* ``exec_prefix`` (``wchar_t*``):
  ``sys.exec_prefix``.
* ``executable`` (``wchar_t*``):
  ``sys.executable``.
* ``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.
* ``isolated`` (``int``):
  If greater than 0, enable isolated mode:

  * ``sys.path`` contains neither the script's directory (computed from
    ``argv[0]`` or the current directory) nor the user's site-packages
    directory.
  * Python REPL doesn't import ``readline`` nor enable default readline
    configuration on interactive prompts.
  * Set ``use_environment`` and ``user_site_directory`` to 0.

* ``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 statistics on ``pymalloc`` memory allocator at exit.
  The option is ignored if Python is built using ``--without-pymalloc``.
* ``pythonpath_env`` (``wchar_t*``):
  Module search paths as a string separated by DELIM (usually ``:``
  character).
  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 overridden by the function computing the
  `Path Configuration`_.
* ``optimization_level`` (``int``):
  Compilation optimization level:

  * 0: Peephole optimizer (and ``__debug__`` is set to ``True``)
  * 1: Remove assertions, set ``__debug__`` to ``False``
  * 2: Strip docstrings

* ``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*``):
  ``sys.prefix``.
* ``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*``):
  ``python3 -c COMMAND`` argument.
* ``run_filename`` (``wchar_t*``):
  ``python3 FILENAME`` argument.
* ``run_module`` (``wchar_t*``):
  ``python3 -m MODULE`` argument.
* ``show_alloc_count`` (``int``):
  Show allocation counts at exit?
  Need a special Python build with ``COUNT_ALLOCS`` macro defined.
* ``show_ref_count`` (``int``):
  Show total reference count at exit?
  Need a debug build of Python (``Py_REF_DEBUG`` macro should be
  defined).
* ``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``):
  ``sys._xoptions``.

The ``legacy_windows_stdio`` field is only available on Windows.
``#ifdef MS_WINDOWS`` macro can be used for Windows specific code.

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
Options`_.

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

* ``_config_init`` (``int``):
  Function used to initialize ``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::

    PyStatus init_python(const char *program_name)
    {
        PyStatus status;

        PyConfig config;
        PyConfig_InitPythonConfig(&config);

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

           Implicitly preinitialize Python. */
        status = PyConfig_SetBytesString(&config, &config.program_name,
                                      program_name);
        if (PyStatus_Exception(status)) {
            goto done;
        }

        /* Read all configuration at once */
        status = PyConfig_Read(&config);
        if (PyStatus_Exception(status)) {
            goto done;
        }

        /* Append our custom search path to sys.path */
        status = PyWideStringList_Append(&config.module_search_paths,
                                      L"/path/to/more/modules");
        if (PyStatus_Exception(status)) {
            goto done;
        }

        /* Override executable computed by PyConfig_Read() */
        status = PyConfig_SetString(&config, &config.executable,
                                    L"/path/to/my_executable");
        if (PyStatus_Exception(status)) {
            goto done;
        }

        status = Py_InitializeFromConfig(&config);

    done:
        PyConfig_Clear(&config);
        return status;
    }

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

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)
    {
        PyStatus status;

        PyConfig config;
        PyConfig_InitPythonConfig(&config);

        config.isolated = 1;

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

        status = Py_InitializeFromConfig(&config);
        if (PyStatus_Exception(status)) {
            goto fail;
        }
        PyConfig_Clear(&config);

        return Py_RunMain();

    fail:
        PyConfig_Clear(&config);
        if (PyStatus_IsExit(status)) {
            return status.exitcode;
        }
        /* Display the error message and exit the process with
           non-zero exit code */
        Py_ExitStatusException(status);
    }

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``

If at least one "output field" is not set, Python computes the path
configuration to fill unset fields. If ``module_search_paths_set`` is
equal to 0, ``module_search_paths`` is overridden and
``module_search_paths_set`` is set to 1.

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 is non-empty.
``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.

``Py_RunMain()`` and ``Py_Main()`` modify ``sys.path``:

* If ``run_filename`` is set and is a directory which contains a
  ``__main__.py`` script, prepend ``run_filename`` to ``sys.path``.
* If ``isolated`` is zero:

  * If ``run_module`` is set, prepend the current directory to
    ``sys.path``. Do nothing if the current directory cannot be read.
  * If ``run_filename`` is set, prepends the directory of the filename
    to ``sys.path``.
  * Otherwise, prepends an empty string to ``sys.path``.

If ``site_import`` is non-zero, ``sys.path`` can be modified by the
``site`` module. If ``user_site_directory`` is non-zero and the user's
site-package directory exists, the ``site`` module appends the user's
site-package directory to ``sys.path``.

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


Py_BytesMain()
--------------

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)

Py_RunMain()
------------

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()``.


Multi-Phase Initialization Private Provisional API
--------------------------------------------------

This section is a private provisional API introducing multi-phase
initialization, the core feature of the :pep:`432`:

* "Core" initialization phase, "bare minimum Python":

  * Builtin types;
  * Builtin exceptions;
  * Builtin and frozen modules;
  * The ``sys`` module is only partially initialized
    (ex: ``sys.path`` doesn't exist yet);

* "Main" initialization phase, Python is fully initialized:

  * Install and configure ``importlib``;
  * Apply the `Path Configuration`_;
  * Install signal handlers;
  * Finish ``sys`` module initialization (ex: create ``sys.stdout`` and
    ``sys.path``);
  * Enable optional features like ``faulthandler`` and ``tracemalloc``;
  * Import the ``site`` module;
  * etc.

Private provisional API:

* ``PyConfig._init_main``: if set to 0, ``Py_InitializeFromConfig()``
  stops at the "Core" initialization phase.
* ``PyStatus _Py_InitializeMain(void)``: move to the "Main"
  initialization phase, finish the Python initialization.

No module is imported during the "Core" phase and the ``importlib``
module is not configured: the `Path Configuration`_ is only applied
during the "Main" phase. It may allow to customize Python in Python to
override or tune the `Path Configuration`_, maybe install a custom
sys.meta_path importer or an import hook, etc.

It may become possible to compute the `Path Configuration`_ in Python,
after the Core phase and before the Main phase, which is one of the PEP
432 motivation.

The "Core" phase is not properly defined: what should be and what should
not be available at this phase is not specified yet. The API is marked
as private and provisional: the API can be modified or even be removed
anytime until a proper public API is designed.

Example running Python code between "Core" and "Main" initialization
phases::

    void init_python(void)
    {
        PyStatus status;

        PyConfig config;
        PyConfig_InitPythonConfig(&config);

        config._init_main = 0;

        /* ... customize 'config' configuration ... */

        status = Py_InitializeFromConfig(&config);
        PyConfig_Clear(&config);
        if (PyStatus_Exception(status)) {
            Py_ExitStatusException(status);
        }

        /* Use sys.stderr because sys.stdout is only created
           by _Py_InitializeMain() */
        int res = PyRun_SimpleString(
            "import sys; "
            "print('Run Python code before _Py_InitializeMain', "
                   "file=sys.stderr)");
        if (res < 0) {
            exit(1);
        }

        /* ... put more configuration code here ... */

        status = _Py_InitializeMain();
        if (PyStatus_Exception(status)) {
            Py_ExitStatusException(status);
        }
    }


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.


Annexes
=======

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``                           0     **1**
``legacy_windows_fs_encoding``        -1         0
``use_environment``                    0         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``
* ``PySys_AddWarnOption()``
* ``PyConfig.bytes_warning`` (add ``"error::BytesWarning"`` filter if
  greater than 1, add ``"default::BytesWarning`` filter if equals to 1)
* ``-W opt`` command line argument
* ``PYTHONWARNINGS`` environment variable
* ``PyConfig.dev_mode`` (add ``"default"`` filter)

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 opposite 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 opposite of the global
configuration variable value. ``Py_LegacyWindowsStdioFlag`` is only
available on Windows.


Command Line Arguments
----------------------

Usage::

    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``
=================================  ====================================

``PYTHONLEGACYWINDOWSFSENCODING`` and ``PYTHONLEGACYWINDOWSSTDIO`` are
specific to Windows.


Default Python Configuration
-----------------------------

``PyPreConfig_InitPythonConfig()``:

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

``PyConfig_InitPythonConfig()``:

* ``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 Configuration
-------------------------------

``PyPreConfig_InitIsolatedConfig()``:

* ``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

``PyConfig_InitIsolatedConfig()``:

* ``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
Python:

* ``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 only)"
* `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".
* `bpo-29778 <https://bugs.python.org/issue29778>`_: "_Py_CheckPython3
  uses uninitialized dllpath when embedder sets module path with
  Py_SetPath"
* `bpo-30560 <https://bugs.python.org/issue30560>`_: "Add
  Py_SetFatalErrorAbortFunc: Allow embedding program to handle fatal
  errors".
* `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-33135 <https://bugs.python.org/issue33135>`_: "Define field
  prefixes for the various config structs". The PEP now defines well
  how warnings options are handled.
* `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()?"

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>`_:
  "PYTHONDONTWRITEBYTECODE and PYTHONOPTIMIZE have no effect"
* `bpo-32030 <https://bugs.python.org/issue32030>`_: "PEP 432: Rewrite
  Py_Main()"
* `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-22257 <https://bugs.python.org/issue22257>`_: "PEP 432: Redesign
  the interpreter startup sequence"
* `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"


Discussions
===========

* May 2019:

  * `[Python-Dev] PEP 587 "Python Initialization Configuration" version 4
    <https://mail.python.org/pipermail/python-dev/2019-May/157492.html>`_
  * `[Python-Dev] RFC: PEP 587 "Python Initialization Configuration": 3rd version
    <https://mail.python.org/pipermail/python-dev/2019-May/157435.html>`_
  * `Study on applications embedding Python
    <https://mail.python.org/pipermail/python-dev/2019-May/157385.html>`_
  * `[Python-Dev] RFC: PEP 587 "Python Initialization Configuration":
    2nd version
    <https://mail.python.org/pipermail/python-dev/2019-May/157290.html>`_

* March 2019:

  * `[Python-Dev] PEP 587: Python Initialization Configuration
    <https://mail.python.org/pipermail/python-dev/2019-March/156892.html>`_
  * `[Python-Dev] New Python Initialization API
    <https://mail.python.org/pipermail/python-dev/2019-March/156884.html>`_

* February 2019:

  * `Adding char* based APIs for Unix
    <https://discuss.python.org/t/adding-char-based-apis-for-unix/916>`_

* July-August 2018:

  * July: `[Python-Dev] New _Py_InitializeFromConfig() function (PEP 432)
    <https://mail.python.org/pipermail/python-dev/2018-July/154882.html>`__
  * August: `[Python-Dev] New _Py_InitializeFromConfig() function (PEP 432)
    <https://mail.python.org/pipermail/python-dev/2018-August/154896.html>`__

Version History
===============

* Version 5:

  * Rename ``PyInitError`` to ``PyStatus``
  * Rename ``PyInitError_Failed()`` to ``PyStatus_Exception()``
  * Rename ``Py_ExitInitError()`` to ``Py_ExitStatusException()``
  * Add ``PyPreConfig._config_init`` private field.
  * Fix Python Configuration default values: isolated=0
    and use_environment=1, instead of -1.
  * Add "Multi-Phase Initialization Private Provisional API"
    and "Discussions" sections

* 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
    functions:

    * ``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()``
    functions.
  * Remove the "Constant PyConfig" section. Remove
    ``Py_InitializeFromArgs()`` and ``Py_InitializeFromBytesArgs()``
    functions.

* 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
    ``PyConfig_SetBytesArgv()``.
  * 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
  ``PyWideStringList``.
* Version 1: Initial version.

Acceptance
==========

:pep:`587` was `accepted by Thomas Wouters on May 26, 2019
<https://mail.python.org/pipermail/python-dev/2019-May/157721.html>`_.


Copyright
=========

This document has been placed in the public domain.