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cpython/Doc/c-api/init_config.rst
Victor Stinner 5ed7827b16
bpo-44441: _PyImport_Fini2() resets PyImport_Inittab (GH-26874) (GH-26878) 
Py_RunMain() now resets PyImport_Inittab to its initial value at
exit. It must be possible to call PyImport_AppendInittab() or
PyImport_ExtendInittab() at each Python initialization.

(cherry picked from commit 489699ca05)
2021-06-23 17:47:33 +02:00

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.. highlight:: c
.. _init-config:
***********************************
Python Initialization Configuration
***********************************
.. versionadded:: 3.8
Structures:
* :c:type:`PyConfig`
* :c:type:`PyPreConfig`
* :c:type:`PyStatus`
* :c:type:`PyWideStringList`
Functions:
* :c:func:`PyConfig_Clear`
* :c:func:`PyConfig_InitIsolatedConfig`
* :c:func:`PyConfig_InitPythonConfig`
* :c:func:`PyConfig_Read`
* :c:func:`PyConfig_SetArgv`
* :c:func:`PyConfig_SetBytesArgv`
* :c:func:`PyConfig_SetBytesString`
* :c:func:`PyConfig_SetString`
* :c:func:`PyConfig_SetWideStringList`
* :c:func:`PyPreConfig_InitIsolatedConfig`
* :c:func:`PyPreConfig_InitPythonConfig`
* :c:func:`PyStatus_Error`
* :c:func:`PyStatus_Exception`
* :c:func:`PyStatus_Exit`
* :c:func:`PyStatus_IsError`
* :c:func:`PyStatus_IsExit`
* :c:func:`PyStatus_NoMemory`
* :c:func:`PyStatus_Ok`
* :c:func:`PyWideStringList_Append`
* :c:func:`PyWideStringList_Insert`
* :c:func:`Py_ExitStatusException`
* :c:func:`Py_InitializeFromConfig`
* :c:func:`Py_PreInitialize`
* :c:func:`Py_PreInitializeFromArgs`
* :c:func:`Py_PreInitializeFromBytesArgs`
* :c:func:`Py_RunMain`
* :c:func:`Py_GetArgcArgv`
The preconfiguration (``PyPreConfig`` type) is stored in
``_PyRuntime.preconfig`` and the configuration (``PyConfig`` type) is stored in
``PyInterpreterState.config``.
See also :ref:`Initialization, Finalization, and Threads <initialization>`.
.. seealso::
:pep:`587` "Python Initialization Configuration".
PyWideStringList
----------------
.. c:type:: PyWideStringList
List of ``wchar_t*`` strings.
If *length* is non-zero, *items* must be non-``NULL`` and all strings must be
non-``NULL``.
Methods:
.. c:function:: PyStatus PyWideStringList_Append(PyWideStringList *list, const wchar_t *item)
Append *item* to *list*.
Python must be preinitialized to call this function.
.. c:function:: PyStatus PyWideStringList_Insert(PyWideStringList *list, Py_ssize_t index, const wchar_t *item)
Insert *item* into *list* at *index*.
If *index* is greater than or equal to *list* length, append *item* to
*list*.
*index* must be greater than or equal to 0.
Python must be preinitialized to call this function.
Structure fields:
.. c:member:: Py_ssize_t length
List length.
.. c:member:: wchar_t** items
List items.
PyStatus
--------
.. c:type:: PyStatus
Structure to store an initialization function status: success, error
or exit.
For an error, it can store the C function name which created the error.
Structure fields:
.. c:member:: int exitcode
Exit code. Argument passed to ``exit()``.
.. c:member:: const char *err_msg
Error message.
.. c:member:: const char *func
Name of the function which created an error, can be ``NULL``.
Functions to create a status:
.. c:function:: PyStatus PyStatus_Ok(void)
Success.
.. c:function:: PyStatus PyStatus_Error(const char *err_msg)
Initialization error with a message.
.. c:function:: PyStatus PyStatus_NoMemory(void)
Memory allocation failure (out of memory).
.. c:function:: PyStatus PyStatus_Exit(int exitcode)
Exit Python with the specified exit code.
Functions to handle a status:
.. c:function:: int PyStatus_Exception(PyStatus status)
Is the status an error or an exit? If true, the exception must be
handled; by calling :c:func:`Py_ExitStatusException` for example.
.. c:function:: int PyStatus_IsError(PyStatus status)
Is the result an error?
.. c:function:: int PyStatus_IsExit(PyStatus status)
Is the result an exit?
.. c:function:: void Py_ExitStatusException(PyStatus status)
Call ``exit(exitcode)`` if *status* is an exit. Print the error
message and exit with a non-zero exit code if *status* is an error. Must
only be called if ``PyStatus_Exception(status)`` is non-zero.
.. note::
Internally, Python uses macros which set ``PyStatus.func``,
whereas functions to create a status set ``func`` to ``NULL``.
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;
}
PyPreConfig
-----------
.. c:type:: PyPreConfig
Structure used to preinitialize Python:
* Set the Python memory allocator
* Configure the LC_CTYPE locale
* Set the UTF-8 mode
Function to initialize a preconfiguration:
.. c:function:: void PyPreConfig_InitPythonConfig(PyPreConfig *preconfig)
Initialize the preconfiguration with :ref:`Python Configuration
<init-python-config>`.
.. c:function:: void PyPreConfig_InitIsolatedConfig(PyPreConfig *preconfig)
Initialize the preconfiguration with :ref:`Isolated Configuration
<init-isolated-conf>`.
Structure fields:
.. c:member:: int allocator
Name of the memory allocator:
* ``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``): :ref:`Python pymalloc memory
allocator <pymalloc>`
* ``PYMEM_ALLOCATOR_PYMALLOC_DEBUG`` (``6``): :ref:`Python pymalloc
memory allocator <pymalloc>` with debug hooks
``PYMEM_ALLOCATOR_PYMALLOC`` and ``PYMEM_ALLOCATOR_PYMALLOC_DEBUG``
are not supported if Python is configured using ``--without-pymalloc``
See :ref:`Memory Management <memory>`.
.. c:member:: int configure_locale
Set the LC_CTYPE locale to the user preferred locale? If equals to 0, set
:c:member:`coerce_c_locale` and :c:member:`coerce_c_locale_warn` to 0.
.. c:member:: int coerce_c_locale
If equals to 2, coerce the C locale; if equals to 1, read the LC_CTYPE
locale to decide if it should be coerced.
.. c:member:: int coerce_c_locale_warn
If non-zero, emit a warning if the C locale is coerced.
.. c:member:: int dev_mode
See :c:member:`PyConfig.dev_mode`.
.. c:member:: int isolated
See :c:member:`PyConfig.isolated`.
.. c:member:: int legacy_windows_fs_encoding (Windows only)
If non-zero, disable UTF-8 Mode, set the Python filesystem encoding to
``mbcs``, set the filesystem error handler to ``replace``.
Only available on Windows. ``#ifdef MS_WINDOWS`` macro can be used for
Windows specific code.
.. c:member:: int parse_argv
If non-zero, :c:func:`Py_PreInitializeFromArgs` and
:c:func:`Py_PreInitializeFromBytesArgs` parse their ``argv`` argument the
same way the regular Python parses command line arguments: see
:ref:`Command Line Arguments <using-on-cmdline>`.
.. c:member:: int use_environment
See :c:member:`PyConfig.use_environment`.
.. c:member:: int utf8_mode
If non-zero, enable the UTF-8 mode.
Preinitialization with PyPreConfig
----------------------------------
Functions to preinitialize Python:
.. c:function:: PyStatus Py_PreInitialize(const PyPreConfig *preconfig)
Preinitialize Python from *preconfig* preconfiguration.
.. c:function:: PyStatus Py_PreInitializeFromBytesArgs(const PyPreConfig *preconfig, int argc, char * const *argv)
Preinitialize Python from *preconfig* preconfiguration and command line
arguments (bytes strings).
.. c:function:: PyStatus Py_PreInitializeFromArgs(const PyPreConfig *preconfig, int argc, wchar_t * const * argv)
Preinitialize Python from *preconfig* preconfiguration and command line
arguments (wide strings).
The caller is responsible to handle exceptions (error or exit) using
:c:func:`PyStatus_Exception` and :c:func:`Py_ExitStatusException`.
For :ref:`Python Configuration <init-python-config>`
(:c:func:`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 :option:`-X utf8 <-X>` command line option
enables the UTF-8 Mode.
``PyMem_SetAllocator()`` can be called after :c:func:`Py_PreInitialize` and
before :c:func:`Py_InitializeFromConfig` to install a custom memory allocator.
It can be called before :c:func:`Py_PreInitialize` if
:c:member:`PyPreConfig.allocator` is set to ``PYMEM_ALLOCATOR_NOT_SET``.
Python memory allocation functions like :c:func:`PyMem_RawMalloc` must not be
used before Python preinitialization, whereas calling directly ``malloc()`` and
``free()`` is always safe. :c:func:`Py_DecodeLocale` must not be called before
the preinitialization.
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();
PyConfig
--------
.. c:type:: PyConfig
Structure containing most parameters to configure Python.
Structure methods:
.. c:function:: void PyConfig_InitPythonConfig(PyConfig *config)
Initialize configuration with :ref:`Python Configuration
<init-python-config>`.
.. c:function:: void PyConfig_InitIsolatedConfig(PyConfig *config)
Initialize configuration with :ref:`Isolated Configuration
<init-isolated-conf>`.
.. c:function:: 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.
.. c:function:: 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.
.. c:function:: PyStatus PyConfig_SetArgv(PyConfig *config, int argc, wchar_t * const *argv)
Set command line arguments from wide character strings.
Preinitialize Python if needed.
.. c:function:: PyStatus PyConfig_SetBytesArgv(PyConfig *config, int argc, char * const *argv)
Set command line arguments: decode bytes using :c:func:`Py_DecodeLocale`.
Preinitialize Python if needed.
.. c:function:: PyStatus PyConfig_SetWideStringList(PyConfig *config, PyWideStringList *list, Py_ssize_t length, wchar_t **items)
Set the list of wide strings *list* to *length* and *items*.
Preinitialize Python if needed.
.. c:function:: PyStatus PyConfig_Read(PyConfig *config)
Read all Python configuration.
Fields which are already initialized are left unchanged.
Preinitialize Python if needed.
.. c:function:: 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 :c:type:`PyConfig`.
If configuration fields which are in common with :c:type:`PyPreConfig` are
tuned, they must be set before calling a :c:type:`PyConfig` method:
* :c:member:`~PyConfig.dev_mode`
* :c:member:`~PyConfig.isolated`
* :c:member:`~PyConfig.parse_argv`
* :c:member:`~PyConfig.use_environment`
Moreover, if :c:func:`PyConfig_SetArgv` or :c:func:`PyConfig_SetBytesArgv`
is used, this method must be called first, before other methods, since the
preinitialization configuration depends on command line arguments (if
:c:member:`parse_argv` is non-zero).
The caller of these methods is responsible to handle exceptions (error or
exit) using ``PyStatus_Exception()`` and ``Py_ExitStatusException()``.
Structure fields:
.. c:member:: PyWideStringList argv
Command line arguments, :data:`sys.argv`. See
:c:member:`~PyConfig.parse_argv` to parse :c:member:`~PyConfig.argv` the
same way the regular Python parses Python command line arguments. If
:c:member:`~PyConfig.argv` is empty, an empty string is added to ensure
that :data:`sys.argv` always exists and is never empty.
.. c:member:: wchar_t* base_exec_prefix
:data:`sys.base_exec_prefix`.
.. c:member:: wchar_t* base_executable
:data:`sys._base_executable`: ``__PYVENV_LAUNCHER__`` environment
variable value, or copy of :c:member:`PyConfig.executable`.
.. c:member:: wchar_t* base_prefix
:data:`sys.base_prefix`.
.. c:member:: wchar_t* platlibdir
:data:`sys.platlibdir`: platform library directory name, set at configure time
by ``--with-platlibdir``, overrideable by the ``PYTHONPLATLIBDIR``
environment variable.
.. versionadded:: 3.9
.. c:member:: int buffered_stdio
If equals to 0, enable unbuffered mode, making the stdout and stderr
streams unbuffered.
stdin is always opened in buffered mode.
.. c:member:: int bytes_warning
If equals to 1, issue a warning when comparing :class:`bytes` or
:class:`bytearray` with :class:`str`, or comparing :class:`bytes` with
:class:`int`. If equal or greater to 2, raise a :exc:`BytesWarning`
exception.
.. c:member:: wchar_t* check_hash_pycs_mode
Control the validation behavior of hash-based ``.pyc`` files (see
:pep:`552`): :option:`--check-hash-based-pycs` command line option value.
Valid values: ``always``, ``never`` and ``default``.
The default value is: ``default``.
.. c:member:: int configure_c_stdio
If non-zero, configure C standard streams (``stdio``, ``stdout``,
``stdout``). For example, set their mode to ``O_BINARY`` on Windows.
.. c:member:: int dev_mode
If non-zero, enable the :ref:`Python Development Mode <devmode>`.
.. c:member:: int dump_refs
If non-zero, dump all objects which are still alive at exit.
``Py_TRACE_REFS`` macro must be defined in build.
.. c:member:: wchar_t* exec_prefix
:data:`sys.exec_prefix`.
.. c:member:: wchar_t* executable
:data:`sys.executable`.
.. c:member:: int faulthandler
If non-zero, call :func:`faulthandler.enable` at startup.
.. c:member:: wchar_t* filesystem_encoding
Filesystem encoding, :func:`sys.getfilesystemencoding`.
.. c:member:: wchar_t* filesystem_errors
Filesystem encoding errors, :func:`sys.getfilesystemencodeerrors`.
.. c:member:: unsigned long hash_seed
.. c:member:: int use_hash_seed
Randomized hash function seed.
If :c:member:`~PyConfig.use_hash_seed` is zero, a seed is chosen randomly
at Pythonstartup, and :c:member:`~PyConfig.hash_seed` is ignored.
.. c:member:: wchar_t* home
Python home directory.
Initialized from :envvar:`PYTHONHOME` environment variable value by
default.
.. c:member:: int import_time
If non-zero, profile import time.
.. c:member:: int inspect
Enter interactive mode after executing a script or a command.
.. c:member:: int install_signal_handlers
Install signal handlers?
.. c:member:: int interactive
Interactive mode.
.. c:member:: int isolated
If greater than 0, enable isolated mode:
* :data:`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 :mod:`readline` nor enable default readline
configuration on interactive prompts.
* Set :c:member:`~PyConfig.use_environment` and
:c:member:`~PyConfig.user_site_directory` to 0.
.. c:member:: int legacy_windows_stdio
If non-zero, use :class:`io.FileIO` instead of
:class:`io.WindowsConsoleIO` for :data:`sys.stdin`, :data:`sys.stdout`
and :data:`sys.stderr`.
Only available on Windows. ``#ifdef MS_WINDOWS`` macro can be used for
Windows specific code.
.. c:member:: int malloc_stats
If non-zero, dump statistics on :ref:`Python pymalloc memory allocator
<pymalloc>` at exit.
The option is ignored if Python is built using ``--without-pymalloc``.
.. c:member:: wchar_t* pythonpath_env
Module search paths as a string separated by ``DELIM``
(:data:`os.path.pathsep`).
Initialized from :envvar:`PYTHONPATH` environment variable value by
default.
.. c:member:: PyWideStringList module_search_paths
.. c:member:: int module_search_paths_set
:data:`sys.path`. If :c:member:`~PyConfig.module_search_paths_set` is
equal to 0, the :c:member:`~PyConfig.module_search_paths` is overridden
by the function calculating the :ref:`Path Configuration
<init-path-config>`.
.. c:member:: int optimization_level
Compilation optimization level:
* 0: Peephole optimizer (and ``__debug__`` is set to ``True``)
* 1: Remove assertions, set ``__debug__`` to ``False``
* 2: Strip docstrings
.. c:member:: int parse_argv
If non-zero, parse :c:member:`~PyConfig.argv` the same way the regular
Python command line arguments, and strip Python arguments from
:c:member:`~PyConfig.argv`: see :ref:`Command Line Arguments
<using-on-cmdline>`.
.. c:member:: int parser_debug
If non-zero, turn on parser debugging output (for expert only, depending
on compilation options).
.. c:member:: int pathconfig_warnings
If equal to 0, suppress warnings when calculating the :ref:`Path
Configuration <init-path-config>` (Unix only, Windows does not log any
warning). Otherwise, warnings are written into ``stderr``.
.. c:member:: wchar_t* prefix
:data:`sys.prefix`.
.. c:member:: wchar_t* program_name
Program name. Used to initialize :c:member:`~PyConfig.executable`, and in
early error messages.
.. c:member:: wchar_t* pycache_prefix
:data:`sys.pycache_prefix`: ``.pyc`` cache prefix.
If ``NULL``, :data:`sys.pycache_prefix` is set to ``None``.
.. c:member:: int quiet
Quiet mode. For example, don't display the copyright and version messages
in interactive mode.
.. c:member:: wchar_t* run_command
``python3 -c COMMAND`` argument. Used by :c:func:`Py_RunMain`.
.. c:member:: wchar_t* run_filename
``python3 FILENAME`` argument. Used by :c:func:`Py_RunMain`.
.. c:member:: wchar_t* run_module
``python3 -m MODULE`` argument. Used by :c:func:`Py_RunMain`.
.. c:member:: int show_ref_count
Show total reference count at exit?
Set to 1 by :option:`-X showrefcount <-X>` command line option.
Need a debug build of Python (``Py_REF_DEBUG`` macro must be defined).
.. c:member:: int site_import
Import the :mod:`site` module at startup?
.. c:member:: int skip_source_first_line
Skip the first line of the source?
.. c:member:: wchar_t* stdio_encoding
.. c:member:: wchar_t* stdio_errors
Encoding and encoding errors of :data:`sys.stdin`, :data:`sys.stdout` and
:data:`sys.stderr`.
.. c:member:: int tracemalloc
If non-zero, call :func:`tracemalloc.start` at startup.
.. c:member:: int use_environment
If greater than 0, use :ref:`environment variables <using-on-envvars>`.
.. c:member:: int user_site_directory
If non-zero, add user site directory to :data:`sys.path`.
.. c:member:: int verbose
If non-zero, enable verbose mode.
.. c:member:: PyWideStringList warnoptions
:data:`sys.warnoptions`: options of the :mod:`warnings` module to build
warnings filters: lowest to highest priority.
The :mod:`warnings` module adds :data:`sys.warnoptions` in the reverse
order: the last :c:member:`PyConfig.warnoptions` item becomes the first
item of :data:`warnings.filters` which is checked first (highest
priority).
.. c:member:: int write_bytecode
If non-zero, write ``.pyc`` files.
:data:`sys.dont_write_bytecode` is initialized to the inverted value of
:c:member:`~PyConfig.write_bytecode`.
.. c:member:: PyWideStringList xoptions
:data:`sys._xoptions`.
.. c:member:: int _use_peg_parser
Enable PEG parser? Default: 1.
Set to 0 by :option:`-X oldparser <-X>` and :envvar:`PYTHONOLDPARSER`.
See also :pep:`617`.
.. deprecated-removed:: 3.9 3.10
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 :ref:`Command Line Arguments
<using-on-cmdline>`.
The ``xoptions`` options are parsed to set other options: see :option:`-X`
option.
.. versionchanged:: 3.9
The ``show_alloc_count`` field has been removed.
Initialization with PyConfig
----------------------------
Function to initialize Python:
.. c:function:: PyStatus Py_InitializeFromConfig(const PyConfig *config)
Initialize Python from *config* configuration.
The caller is responsible to handle exceptions (error or exit) using
:c:func:`PyStatus_Exception` and :c:func:`Py_ExitStatusException`.
If :c:func:`PyImport_FrozenModules`, :c:func:`PyImport_AppendInittab` or
:c:func:`PyImport_ExtendInittab` are used, they must be set or called after
Python preinitialization and before the Python initialization. If Python is
initialized multiple times, :c:func:`PyImport_AppendInittab` or
:c:func:`PyImport_ExtendInittab` must be called before each Python
initialization.
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);
}
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;
}
.. _init-isolated-conf:
Isolated Configuration
----------------------
:c:func:`PyPreConfig_InitIsolatedConfig` and
:c:func:`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, command line arguments (:c:member:`PyConfig.argv` is not parsed)
and user site directory. The C standard streams (ex: ``stdout``) and the
LC_CTYPE locale are left unchanged. Signal handlers are not installed.
Configuration files are still used with this configuration. Set the
:ref:`Path Configuration <init-path-config>` ("output fields") to ignore these
configuration files and avoid the function computing the default path
configuration.
.. _init-python-config:
Python Configuration
--------------------
:c:func:`PyPreConfig_InitPythonConfig` and :c:func:`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, :envvar:`PYTHONUTF8` and
:envvar:`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);
}
.. _init-path-config:
Path Configuration
------------------
:c:type:`PyConfig` contains multiple fields for the path configuration:
* Path configuration inputs:
* :c:member:`PyConfig.home`
* :c:member:`PyConfig.platlibdir`
* :c:member:`PyConfig.pathconfig_warnings`
* :c:member:`PyConfig.program_name`
* :c:member:`PyConfig.pythonpath_env`
* current working directory: to get absolute paths
* ``PATH`` environment variable to get the program full path
(from :c:member:`PyConfig.program_name`)
* ``__PYVENV_LAUNCHER__`` environment variable
* (Windows only) Application paths in the registry under
"Software\Python\PythonCore\X.Y\PythonPath" of HKEY_CURRENT_USER and
HKEY_LOCAL_MACHINE (where X.Y is the Python version).
* Path configuration output fields:
* :c:member:`PyConfig.base_exec_prefix`
* :c:member:`PyConfig.base_executable`
* :c:member:`PyConfig.base_prefix`
* :c:member:`PyConfig.exec_prefix`
* :c:member:`PyConfig.executable`
* :c:member:`PyConfig.module_search_paths_set`,
:c:member:`PyConfig.module_search_paths`
* :c:member:`PyConfig.prefix`
If at least one "output field" is not set, Python calculates the path
configuration to fill unset fields. If
:c:member:`~PyConfig.module_search_paths_set` is equal to 0,
:c:member:`~PyConfig.module_search_paths` is overridden and
:c:member:`~PyConfig.module_search_paths_set` is set to 1.
It is possible to completely ignore the function calculating 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 :c:member:`~PyConfig.pathconfig_warnings` to 0 to suppress warnings when
calculating the path configuration (Unix only, Windows does not log any warning).
If :c:member:`~PyConfig.base_prefix` or :c:member:`~PyConfig.base_exec_prefix`
fields are not set, they inherit their value from :c:member:`~PyConfig.prefix`
and :c:member:`~PyConfig.exec_prefix` respectively.
:c:func:`Py_RunMain` and :c:func:`Py_Main` modify :data:`sys.path`:
* If :c:member:`~PyConfig.run_filename` is set and is a directory which contains a
``__main__.py`` script, prepend :c:member:`~PyConfig.run_filename` to
:data:`sys.path`.
* If :c:member:`~PyConfig.isolated` is zero:
* If :c:member:`~PyConfig.run_module` is set, prepend the current directory
to :data:`sys.path`. Do nothing if the current directory cannot be read.
* If :c:member:`~PyConfig.run_filename` is set, prepend the directory of the
filename to :data:`sys.path`.
* Otherwise, prepend an empty string to :data:`sys.path`.
If :c:member:`~PyConfig.site_import` is non-zero, :data:`sys.path` can be
modified by the :mod:`site` module. If
:c:member:`~PyConfig.user_site_directory` is non-zero and the user's
site-package directory exists, the :mod:`site` module appends the user's
site-package directory to :data:`sys.path`.
The following configuration files are used by the path configuration:
* ``pyvenv.cfg``
* ``python._pth`` (Windows only)
* ``pybuilddir.txt`` (Unix only)
The ``__PYVENV_LAUNCHER__`` environment variable is used to set
:c:member:`PyConfig.base_executable`
Py_RunMain()
------------
.. c:function:: int Py_RunMain(void)
Execute the command (:c:member:`PyConfig.run_command`), the script
(:c:member:`PyConfig.run_filename`) or the module
(:c:member:`PyConfig.run_module`) specified on the command line or in the
configuration.
By default and when if :option:`-i` option is used, run the REPL.
Finally, finalizes Python and returns an exit status that can be passed to
the ``exit()`` function.
See :ref:`Python Configuration <init-python-config>` for an example of
customized Python always running in isolated mode using
:c:func:`Py_RunMain`.
Py_GetArgcArgv()
----------------
.. c:function:: void Py_GetArgcArgv(int *argc, wchar_t ***argv)
Get the original command line arguments, before Python modified them.
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 :mod:`sys` module is only partially initialized
(ex: :data:`sys.path` doesn't exist yet).
* "Main" initialization phase, Python is fully initialized:
* Install and configure :mod:`importlib`;
* Apply the :ref:`Path Configuration <init-path-config>`;
* Install signal handlers;
* Finish :mod:`sys` module initialization (ex: create :data:`sys.stdout`
and :data:`sys.path`);
* Enable optional features like :mod:`faulthandler` and :mod:`tracemalloc`;
* Import the :mod:`site` module;
* etc.
Private provisional API:
* :c:member:`PyConfig._init_main`: if set to 0,
:c:func:`Py_InitializeFromConfig` stops at the "Core" initialization phase.
* :c:member:`PyConfig._isolated_interpreter`: if non-zero,
disallow threads, subprocesses and fork.
.. c:function:: 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 :ref:`Path Configuration <init-path-config>` is only
applied during the "Main" phase. It may allow to customize Python in Python to
override or tune the :ref:`Path Configuration <init-path-config>`, maybe
install a custom :data:`sys.meta_path` importer or an import hook, etc.
It may become possible to calculatin the :ref:`Path Configuration
<init-path-config>` 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);
}
}
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