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.. highlight:: c
.. _init-config:
***********************************
Python Initialization Configuration
***********************************
.. versionadded:: 3.8
Python can be initialized with :c:func:`Py_InitializeFromConfig` and the
:c:type:`PyConfig` structure. It can be preinitialized with
:c:func:`Py_PreInitialize` and the :c:type:`PyPreConfig` structure.
There are two kinds of configuration:
* The :ref:`Python Configuration <init-python-config>` can be used to build a
customized Python which behaves as the regular Python. For example,
environments variables and command line arguments are used to configure
Python.
* The :ref:`Isolated Configuration <init-isolated-conf>` can be used to embed
Python into an application. It isolates Python from the system. For example,
environments variables are ignored, the LC_CTYPE locale is left unchanged and
no signal handler is registered.
The :c:func:`Py_RunMain` function can be used to write a customized Python
program.
See also :ref:`Initialization, Finalization, and Threads <initialization>`.
.. seealso::
:pep:`587` "Python Initialization Configuration".
Example
=======
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 exception;
}
status = Py_InitializeFromConfig(&config);
if (PyStatus_Exception(status)) {
goto exception;
}
PyConfig_Clear(&config);
return Py_RunMain();
exception:
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);
}
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.
*err_msg* must not be ``NULL``.
.. 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.
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 Python memory allocators:
* ``PYMEM_ALLOCATOR_NOT_SET`` (``0``): don't change memory allocators
(use defaults).
* ``PYMEM_ALLOCATOR_DEFAULT`` (``1``): :ref:`default memory allocators
<default-memory-allocators>`.
* ``PYMEM_ALLOCATOR_DEBUG`` (``2``): :ref:`default memory allocators
<default-memory-allocators>` with :ref:`debug hooks
<pymem-debug-hooks>`.
* ``PYMEM_ALLOCATOR_MALLOC`` (``3``): use ``malloc()`` of the C library.
* ``PYMEM_ALLOCATOR_MALLOC_DEBUG`` (``4``): force usage of
``malloc()`` with :ref:`debug hooks <pymem-debug-hooks>`.
* ``PYMEM_ALLOCATOR_PYMALLOC`` (``5``): :ref:`Python pymalloc memory
allocator <pymalloc>`.
* ``PYMEM_ALLOCATOR_PYMALLOC_DEBUG`` (``6``): :ref:`Python pymalloc
memory allocator <pymalloc>` with :ref:`debug hooks
<pymem-debug-hooks>`.
``PYMEM_ALLOCATOR_PYMALLOC`` and ``PYMEM_ALLOCATOR_PYMALLOC_DEBUG`` are
not supported if Python is :option:`configured using --without-pymalloc
<--without-pymalloc>`.
See :ref:`Memory Management <memory>`.
Default: ``PYMEM_ALLOCATOR_NOT_SET``.
.. c:member:: int configure_locale
Set the LC_CTYPE locale to the user preferred locale?
If equals to 0, set :c:member:`~PyPreConfig.coerce_c_locale` and
:c:member:`~PyPreConfig.coerce_c_locale_warn` members to 0.
See the :term:`locale encoding`.
Default: ``1`` in Python config, ``0`` in isolated config.
.. 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.
See the :term:`locale encoding`.
Default: ``-1`` in Python config, ``0`` in isolated config.
.. c:member:: int coerce_c_locale_warn
If non-zero, emit a warning if the C locale is coerced.
Default: ``-1`` in Python config, ``0`` in isolated config.
.. c:member:: int dev_mode
If non-zero, enables the :ref:`Python Development Mode <devmode>`:
see :c:member:`PyConfig.dev_mode`.
Default: ``-1`` in Python mode, ``0`` in isolated mode.
.. c:member:: int isolated
Isolated mode: see :c:member:`PyConfig.isolated`.
Default: ``0`` in Python mode, ``1`` in isolated mode.
.. c:member:: int legacy_windows_fs_encoding
If non-zero:
* Set :c:member:`PyPreConfig.utf8_mode` to ``0``,
* Set :c:member:`PyConfig.filesystem_encoding` to ``"mbcs"``,
* Set :c:member:`PyConfig.filesystem_errors` to ``"replace"``.
Initialized the from :envvar:`PYTHONLEGACYWINDOWSFSENCODING` environment
variable value.
Only available on Windows. ``#ifdef MS_WINDOWS`` macro can be used for
Windows specific code.
Default: ``0``.
.. 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>`.
Default: ``1`` in Python config, ``0`` in isolated config.
.. c:member:: int use_environment
Use :ref:`environment variables <using-on-envvars>`? See
:c:member:`PyConfig.use_environment`.
Default: ``1`` in Python config and ``0`` in isolated config.
.. c:member:: int utf8_mode
If non-zero, enable the :ref:`Python UTF-8 Mode <utf8-mode>`.
Set by the :option:`-X utf8 <-X>` command line option and the
:envvar:`PYTHONUTF8` environment variable.
Default: ``-1`` in Python config and ``0`` in isolated config.
.. _c-preinit:
Preinitialize Python with PyPreConfig
=====================================
The preinitialization of Python:
* Set the Python memory allocators (:c:member:`PyPreConfig.allocator`)
* Configure the LC_CTYPE locale (:term:`locale encoding`)
* Set the :ref:`Python UTF-8 Mode <utf8-mode>`
(:c:member:`PyPreConfig.utf8_mode`)
The current preconfiguration (``PyPreConfig`` type) is stored in
``_PyRuntime.preconfig``.
Functions to preinitialize Python:
.. c:function:: PyStatus Py_PreInitialize(const PyPreConfig *preconfig)
Preinitialize Python from *preconfig* preconfiguration.
*preconfig* must not be ``NULL``.
.. c:function:: PyStatus Py_PreInitializeFromBytesArgs(const PyPreConfig *preconfig, int argc, char * const *argv)
Preinitialize Python from *preconfig* preconfiguration.
Parse *argv* command line arguments (bytes strings) if
:c:member:`~PyPreConfig.parse_argv` of *preconfig* is non-zero.
*preconfig* must not be ``NULL``.
.. c:function:: PyStatus Py_PreInitializeFromArgs(const PyPreConfig *preconfig, int argc, wchar_t * const * argv)
Preinitialize Python from *preconfig* preconfiguration.
Parse *argv* command line arguments (wide strings) if
:c:member:`~PyPreConfig.parse_argv` of *preconfig* is non-zero.
*preconfig* must not be ``NULL``.
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 :ref:`Python UTF-8 Mode <utf8-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 the Python preinitialization, whereas calling directly ``malloc()``
and ``free()`` is always safe. :c:func:`Py_DecodeLocale` must not be called
before the Python preinitialization.
Example using the preinitialization to enable
the :ref:`Python UTF-8 Mode <utf8-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 speaks UTF-8 */
Py_Initialize();
/* ... use Python API here ... */
Py_Finalize();
PyConfig
========
.. c:type:: PyConfig
Structure containing most parameters to configure Python.
When done, the :c:func:`PyConfig_Clear` function must be used to release the
configuration memory.
Structure methods:
.. c:function:: void PyConfig_InitPythonConfig(PyConfig *config)
Initialize configuration with the :ref:`Python Configuration
<init-python-config>`.
.. c:function:: void PyConfig_InitIsolatedConfig(PyConfig *config)
Initialize configuration with the :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``.
:ref:`Preinitialize Python <c-preinit>` if needed.
.. c:function:: PyStatus PyConfig_SetBytesString(PyConfig *config, wchar_t * const *config_str, const char *str)
Decode *str* using :c:func:`Py_DecodeLocale` and set the result into
``*config_str``.
:ref:`Preinitialize Python <c-preinit>` if needed.
.. c:function:: PyStatus PyConfig_SetArgv(PyConfig *config, int argc, wchar_t * const *argv)
Set command line arguments (:c:member:`~PyConfig.argv` member of
*config*) from the *argv* list of wide character strings.
:ref:`Preinitialize Python <c-preinit>` if needed.
.. c:function:: PyStatus PyConfig_SetBytesArgv(PyConfig *config, int argc, char * const *argv)
Set command line arguments (:c:member:`~PyConfig.argv` member of
*config*) from the *argv* list of bytes strings. Decode bytes using
:c:func:`Py_DecodeLocale`.
:ref:`Preinitialize Python <c-preinit>` 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*.
:ref:`Preinitialize Python <c-preinit>` if needed.
.. c:function:: PyStatus PyConfig_Read(PyConfig *config)
Read all Python configuration.
Fields which are already initialized are left unchanged.
The :c:func:`PyConfig_Read` function only parses
:c:member:`PyConfig.argv` arguments once: :c:member:`PyConfig.parse_argv`
is set to ``2`` after arguments are parsed. Since Python arguments are
strippped from :c:member:`PyConfig.argv`, parsing arguments twice would
parse the application options as Python options.
:ref:`Preinitialize Python <c-preinit>` if needed.
.. versionchanged:: 3.10
The :c:member:`PyConfig.argv` arguments are now only parsed once,
:c:member:`PyConfig.parse_argv` is set to ``2`` after arguments are
parsed, and arguments are only parsed if
:c:member:`PyConfig.parse_argv` equals ``1``.
.. c:function:: void PyConfig_Clear(PyConfig *config)
Release configuration memory.
Most ``PyConfig`` methods :ref:`preinitialize Python <c-preinit>` if needed.
In that case, the Python preinitialization configuration
(:c:type:`PyPreConfig`) 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 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`.
Set :c:member:`~PyConfig.parse_argv` to ``1`` to parse
:c:member:`~PyConfig.argv` the same way the regular Python parses Python
command line arguments and then to strip Python arguments from
:c:member:`~PyConfig.argv`.
If :c:member:`~PyConfig.argv` is empty, an empty string is added to
ensure that :data:`sys.argv` always exists and is never empty.
Default: ``NULL``.
See also the :c:member:`~PyConfig.orig_argv` member.
.. c:member:: wchar_t* base_exec_prefix
:data:`sys.base_exec_prefix`.
Default: ``NULL``.
Part of the :ref:`Python Path Configuration <init-path-config>` output.
.. c:member:: wchar_t* base_executable
Python base executable: :data:`sys._base_executable`.
Set by the :envvar:`__PYVENV_LAUNCHER__` environment variable.
Set from :c:member:`PyConfig.executable` if ``NULL``.
Default: ``NULL``.
Part of the :ref:`Python Path Configuration <init-path-config>` output.
.. c:member:: wchar_t* base_prefix
:data:`sys.base_prefix`.
Default: ``NULL``.
Part of the :ref:`Python Path Configuration <init-path-config>` output.
.. c:member:: int buffered_stdio
If equals to 0 and :c:member:`~PyConfig.configure_c_stdio` is non-zero,
disable buffering on the C streams stdout and stderr.
Set to 0 by the :option:`-u` command line option and the
:envvar:`PYTHONUNBUFFERED` environment variable.
stdin is always opened in buffered mode.
Default: ``1``.
.. 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 in these
cases.
Incremented by the :option:`-b` command line option.
Default: ``0``.
.. c:member:: int warn_default_encoding
If non-zero, emit a :exc:`EncodingWarning` warning when :class:`io.TextIOWrapper`
uses its default encoding. See :ref:`io-encoding-warning` for details.
Default: ``0``.
.. versionadded:: 3.10
.. c:member:: int code_debug_ranges
If equals to ``0``, disables the inclusion of the end line and column
mappings in code objects. Also disables traceback printing carets to
specific error locations.
Set to ``0`` by the :envvar:`PYTHONNODEBUGRANGES` environment variable
and by the :option:`-X no_debug_ranges <-X>` command line option.
Default: ``1``.
.. versionadded:: 3.11
.. c:member:: wchar_t* check_hash_pycs_mode
Control the validation behavior of hash-based ``.pyc`` files:
value of the :option:`--check-hash-based-pycs` command line option.
Valid values:
- ``L"always"``: Hash the source file for invalidation regardless of
value of the 'check_source' flag.
- ``L"never"``: Assume that hash-based pycs always are valid.
- ``L"default"``: The 'check_source' flag in hash-based pycs
determines invalidation.
Default: ``L"default"``.
See also :pep:`552` "Deterministic pycs".
.. c:member:: int configure_c_stdio
If non-zero, configure C standard streams:
* On Windows, set the binary mode (``O_BINARY``) on stdin, stdout and
stderr.
* If :c:member:`~PyConfig.buffered_stdio` equals zero, disable buffering
of stdin, stdout and stderr streams.
* If :c:member:`~PyConfig.interactive` is non-zero, enable stream
buffering on stdin and stdout (only stdout on Windows).
Default: ``1`` in Python config, ``0`` in isolated config.
.. c:member:: int dev_mode
If non-zero, enable the :ref:`Python Development Mode <devmode>`.
Default: ``-1`` in Python mode, ``0`` in isolated mode.
.. c:member:: int dump_refs
Dump Python refererences?
If non-zero, dump all objects which are still alive at exit.
Set to ``1`` by the :envvar:`PYTHONDUMPREFS` environment variable.
Need a special build of Python with the ``Py_TRACE_REFS`` macro defined:
see the :option:`configure --with-trace-refs option <--with-trace-refs>`.
Default: ``0``.
.. c:member:: wchar_t* exec_prefix
The site-specific directory prefix where the platform-dependent Python
files are installed: :data:`sys.exec_prefix`.
Default: ``NULL``.
Part of the :ref:`Python Path Configuration <init-path-config>` output.
.. c:member:: wchar_t* executable
The absolute path of the executable binary for the Python interpreter:
:data:`sys.executable`.
Default: ``NULL``.
Part of the :ref:`Python Path Configuration <init-path-config>` output.
.. c:member:: int faulthandler
Enable faulthandler?
If non-zero, call :func:`faulthandler.enable` at startup.
Set to ``1`` by :option:`-X faulthandler <-X>` and the
:envvar:`PYTHONFAULTHANDLER` environment variable.
Default: ``-1`` in Python mode, ``0`` in isolated mode.
.. c:member:: wchar_t* filesystem_encoding
:term:`Filesystem encoding <filesystem encoding and error handler>`:
:func:`sys.getfilesystemencoding`.
On macOS, Android and VxWorks: use ``"utf-8"`` by default.
On Windows: use ``"utf-8"`` by default, or ``"mbcs"`` if
:c:member:`~PyPreConfig.legacy_windows_fs_encoding` of
:c:type:`PyPreConfig` is non-zero.
Default encoding on other platforms:
* ``"utf-8"`` if :c:member:`PyPreConfig.utf8_mode` is non-zero.
* ``"ascii"`` if Python detects that ``nl_langinfo(CODESET)`` announces
the ASCII encoding (or Roman8 encoding on HP-UX), whereas the
``mbstowcs()`` function decodes from a different encoding (usually
Latin1).
* ``"utf-8"`` if ``nl_langinfo(CODESET)`` returns an empty string.
* Otherwise, use the :term:`locale encoding`:
``nl_langinfo(CODESET)`` result.
At Python startup, the encoding name is normalized to the Python codec
name. For example, ``"ANSI_X3.4-1968"`` is replaced with ``"ascii"``.
See also the :c:member:`~PyConfig.filesystem_errors` member.
.. c:member:: wchar_t* filesystem_errors
:term:`Filesystem error handler <filesystem encoding and error handler>`:
:func:`sys.getfilesystemencodeerrors`.
On Windows: use ``"surrogatepass"`` by default, or ``"replace"`` if
:c:member:`~PyPreConfig.legacy_windows_fs_encoding` of
:c:type:`PyPreConfig` is non-zero.
On other platforms: use ``"surrogateescape"`` by default.
Supported error handlers:
* ``"strict"``
* ``"surrogateescape"``
* ``"surrogatepass"`` (only supported with the UTF-8 encoding)
See also the :c:member:`~PyConfig.filesystem_encoding` member.
.. 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 Python startup, and :c:member:`~PyConfig.hash_seed` is ignored.
Set by the :envvar:`PYTHONHASHSEED` environment variable.
Default *use_hash_seed* value: ``-1`` in Python mode, ``0`` in isolated
mode.
.. c:member:: wchar_t* home
Python home directory.
If :c:func:`Py_SetPythonHome` has been called, use its argument if it is
not ``NULL``.
Set by the :envvar:`PYTHONHOME` environment variable.
Default: ``NULL``.
Part of the :ref:`Python Path Configuration <init-path-config>` input.
.. c:member:: int import_time
If non-zero, profile import time.
Set the ``1`` by the :option:`-X importtime <-X>` option and the
:envvar:`PYTHONPROFILEIMPORTTIME` environment variable.
Default: ``0``.
.. c:member:: int inspect
Enter interactive mode after executing a script or a command.
If greater than 0, enable inspect: when a script is passed as first
argument or the -c option is used, enter interactive mode after executing
the script or the command, even when :data:`sys.stdin` does not appear to
be a terminal.
Incremented by the :option:`-i` command line option. Set to ``1`` if the
:envvar:`PYTHONINSPECT` environment variable is non-empty.
Default: ``0``.
.. c:member:: int install_signal_handlers
Install Python signal handlers?
Default: ``1`` in Python mode, ``0`` in isolated mode.
.. c:member:: int interactive
If greater than 0, enable the interactive mode (REPL).
Incremented by the :option:`-i` command line option.
Default: ``0``.
.. 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.
Default: ``0`` in Python mode, ``1`` in isolated mode.
See also :c:member:`PyPreConfig.isolated`.
.. 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`.
Set to ``1`` if the :envvar:`PYTHONLEGACYWINDOWSSTDIO` environment
variable is set to a non-empty string.
Only available on Windows. ``#ifdef MS_WINDOWS`` macro can be used for
Windows specific code.
Default: ``0``.
See also the :pep:`528` (Change Windows console encoding to UTF-8).
.. c:member:: int malloc_stats
If non-zero, dump statistics on :ref:`Python pymalloc memory allocator
<pymalloc>` at exit.
Set to ``1`` by the :envvar:`PYTHONMALLOCSTATS` environment variable.
The option is ignored if Python is :option:`configured using
the --without-pymalloc option <--without-pymalloc>`.
Default: ``0``.
.. c:member:: wchar_t* platlibdir
Platform library directory name: :data:`sys.platlibdir`.
Set by the :envvar:`PYTHONPLATLIBDIR` environment variable.
Default: value of the ``PLATLIBDIR`` macro which is set by the
:option:`configure --with-platlibdir option <--with-platlibdir>`
(default: ``"lib"``).
Part of the :ref:`Python Path Configuration <init-path-config>` input.
.. versionadded:: 3.9
.. c:member:: wchar_t* pythonpath_env
Module search paths (:data:`sys.path`) as a string separated by ``DELIM``
(:data:`os.path.pathsep`).
Set by the :envvar:`PYTHONPATH` environment variable.
Default: ``NULL``.
Part of the :ref:`Python Path Configuration <init-path-config>` input.
.. c:member:: PyWideStringList module_search_paths
.. c:member:: int module_search_paths_set
Module search paths: :data:`sys.path`.
If :c:member:`~PyConfig.module_search_paths_set` is equal to 0, the
function calculating the :ref:`Python Path Configuration <init-path-config>`
overrides the :c:member:`~PyConfig.module_search_paths` and sets
:c:member:`~PyConfig.module_search_paths_set` to ``1``.
Default: empty list (``module_search_paths``) and ``0``
(``module_search_paths_set``).
Part of the :ref:`Python Path Configuration <init-path-config>` output.
.. c:member:: int optimization_level
Compilation optimization level:
* ``0``: Peephole optimizer, set ``__debug__`` to ``True``.
* ``1``: Level 0, remove assertions, set ``__debug__`` to ``False``.
* ``2``: Level 1, strip docstrings.
Incremented by the :option:`-O` command line option. Set to the
:envvar:`PYTHONOPTIMIZE` environment variable value.
Default: ``0``.
.. c:member:: PyWideStringList orig_argv
The list of the original command line arguments passed to the Python
executable: :data:`sys.orig_argv`.
If :c:member:`~PyConfig.orig_argv` list is empty and
:c:member:`~PyConfig.argv` is not a list only containing an empty
string, :c:func:`PyConfig_Read` copies :c:member:`~PyConfig.argv` into
:c:member:`~PyConfig.orig_argv` before modifying
:c:member:`~PyConfig.argv` (if :c:member:`~PyConfig.parse_argv` is
non-zero).
See also the :c:member:`~PyConfig.argv` member and the
:c:func:`Py_GetArgcArgv` function.
Default: empty list.
.. versionadded:: 3.10
.. c:member:: int parse_argv
Parse command line arguments?
If equals to ``1``, parse :c:member:`~PyConfig.argv` the same way the regular
Python parses :ref:`command line arguments <using-on-cmdline>`, and strip
Python arguments from :c:member:`~PyConfig.argv`.
The :c:func:`PyConfig_Read` function only parses
:c:member:`PyConfig.argv` arguments once: :c:member:`PyConfig.parse_argv`
is set to ``2`` after arguments are parsed. Since Python arguments are
strippped from :c:member:`PyConfig.argv`, parsing arguments twice would
parse the application options as Python options.
Default: ``1`` in Python mode, ``0`` in isolated mode.
.. versionchanged:: 3.10
The :c:member:`PyConfig.argv` arguments are now only parsed if
:c:member:`PyConfig.parse_argv` equals to ``1``.
.. c:member:: int parser_debug
Parser debug mode. If greater than 0, turn on parser debugging output (for expert only, depending
on compilation options).
Incremented by the :option:`-d` command line option. Set to the
:envvar:`PYTHONDEBUG` environment variable value.
Default: ``0``.
.. c:member:: int pathconfig_warnings
On Unix, if non-zero, calculating the :ref:`Python Path Configuration
<init-path-config>` can log warnings into ``stderr``. If equals to 0,
suppress these warnings.
It has no effect on Windows.
Default: ``1`` in Python mode, ``0`` in isolated mode.
Part of the :ref:`Python Path Configuration <init-path-config>` input.
.. c:member:: wchar_t* prefix
The site-specific directory prefix where the platform independent Python
files are installed: :data:`sys.prefix`.
Default: ``NULL``.
Part of the :ref:`Python Path Configuration <init-path-config>` output.
.. c:member:: wchar_t* program_name
Program name used to initialize :c:member:`~PyConfig.executable` and in
early error messages during Python initialization.
* If :func:`Py_SetProgramName` has been called, use its argument.
* On macOS, use :envvar:`PYTHONEXECUTABLE` environment variable if set.
* If the ``WITH_NEXT_FRAMEWORK`` macro is defined, use
:envvar:`__PYVENV_LAUNCHER__` environment variable if set.
* Use ``argv[0]`` of :c:member:`~PyConfig.argv` if available and
non-empty.
* Otherwise, use ``L"python"`` on Windows, or ``L"python3"`` on other
platforms.
Default: ``NULL``.
Part of the :ref:`Python Path Configuration <init-path-config>` input.
.. c:member:: wchar_t* pycache_prefix
Directory where cached ``.pyc`` files are written:
:data:`sys.pycache_prefix`.
Set by the :option:`-X pycache_prefix=PATH <-X>` command line option and
the :envvar:`PYTHONPYCACHEPREFIX` environment variable.
If ``NULL``, :data:`sys.pycache_prefix` is set to ``None``.
Default: ``NULL``.
.. c:member:: int quiet
Quiet mode. If greater than 0, don't display the copyright and version at
Python startup in interactive mode.
Incremented by the :option:`-q` command line option.
Default: ``0``.
.. c:member:: wchar_t* run_command
Value of the :option:`-c` command line option.
Used by :c:func:`Py_RunMain`.
Default: ``NULL``.
.. c:member:: wchar_t* run_filename
Filename passed on the command line: trailing command line argument
without :option:`-c` or :option:`-m`.
For example, it is set to ``script.py`` by the ``python3 script.py arg``
command.
Used by :c:func:`Py_RunMain`.
Default: ``NULL``.
.. c:member:: wchar_t* run_module
Value of the :option:`-m` command line option.
Used by :c:func:`Py_RunMain`.
Default: ``NULL``.
.. 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 :ref:`debug build of Python <debug-build>` (the ``Py_REF_DEBUG``
macro must be defined).
Default: ``0``.
.. c:member:: int site_import
Import the :mod:`site` module at startup?
If equal to zero, disable the import of the module site and the
site-dependent manipulations of :data:`sys.path` that it entails.
Also disable these manipulations if the :mod:`site` module is explicitly
imported later (call :func:`site.main` if you want them to be triggered).
Set to ``0`` by the :option:`-S` command line option.
:data:`sys.flags.no_site` is set to the inverted value of
:c:member:`~PyConfig.site_import`.
Default: ``1``.
.. c:member:: int skip_source_first_line
If non-zero, skip the first line of the :c:member:`PyConfig.run_filename`
source.
It allows the usage of non-Unix forms of ``#!cmd``. This is intended for
a DOS specific hack only.
Set to ``1`` by the :option:`-x` command line option.
Default: ``0``.
.. 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` (but :data:`sys.stderr` always uses
``"backslashreplace"`` error handler).
If :c:func:`Py_SetStandardStreamEncoding` has been called, use its
*error* and *errors* arguments if they are not ``NULL``.
Use the :envvar:`PYTHONIOENCODING` environment variable if it is
non-empty.
Default encoding:
* ``"UTF-8"`` if :c:member:`PyPreConfig.utf8_mode` is non-zero.
* Otherwise, use the :term:`locale encoding`.
Default error handler:
* On Windows: use ``"surrogateescape"``.
* ``"surrogateescape"`` if :c:member:`PyPreConfig.utf8_mode` is non-zero,
or if the LC_CTYPE locale is "C" or "POSIX".
* ``"strict"`` otherwise.
.. c:member:: int tracemalloc
Enable tracemalloc?
If non-zero, call :func:`tracemalloc.start` at startup.
Set by :option:`-X tracemalloc=N <-X>` command line option and by the
:envvar:`PYTHONTRACEMALLOC` environment variable.
Default: ``-1`` in Python mode, ``0`` in isolated mode.
.. c:member:: int use_environment
Use :ref:`environment variables <using-on-envvars>`?
If equals to zero, ignore the :ref:`environment variables
<using-on-envvars>`.
Default: ``1`` in Python config and ``0`` in isolated config.
.. c:member:: int user_site_directory
If non-zero, add the user site directory to :data:`sys.path`.
Set to ``0`` by the :option:`-s` and :option:`-I` command line options.
Set to ``0`` by the :envvar:`PYTHONNOUSERSITE` environment variable.
Default: ``1`` in Python mode, ``0`` in isolated mode.
.. c:member:: int verbose
Verbose mode. If greater than 0, print a message each time a module is
imported, showing the place (filename or built-in module) from which
it is loaded.
If greater or equal to 2, print a message for each file that is checked
for when searching for a module. Also provides information on module
cleanup at exit.
Incremented by the :option:`-v` command line option.
Set to the :envvar:`PYTHONVERBOSE` environment variable value.
Default: ``0``.
.. c:member:: PyWideStringList warnoptions
Options of the :mod:`warnings` module to build warnings filters, lowest
to highest priority: :data:`sys.warnoptions`.
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).
The :option:`-W` command line options adds its value to
:c:member:`~PyConfig.warnoptions`, it can be used multiple times.
The :envvar:`PYTHONWARNINGS` environment variable can also be used to add
warning options. Multiple options can be specified, separated by commas
(``,``).
Default: empty list.
.. c:member:: int write_bytecode
If equal to 0, Python won't try to write ``.pyc`` files on the import of
source modules.
Set to ``0`` by the :option:`-B` command line option and the
:envvar:`PYTHONDONTWRITEBYTECODE` environment variable.
:data:`sys.dont_write_bytecode` is initialized to the inverted value of
:c:member:`~PyConfig.write_bytecode`.
Default: ``1``.
.. c:member:: PyWideStringList xoptions
Values of the :option:`-X` command line options: :data:`sys._xoptions`.
Default: empty list.
If :c:member:`~PyConfig.parse_argv` is non-zero, :c:member:`~PyConfig.argv`
arguments are parsed the same way the regular Python parses :ref:`command line
arguments <using-on-cmdline>`, and Python arguments are stripped from
:c:member:`~PyConfig.argv`.
The :c:member:`~PyConfig.xoptions` options are parsed to set other options: see
the :option:`-X` command line 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.
The current configuration (``PyConfig`` type) is stored in
``PyInterpreterState.config``.
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 exception;
}
status = Py_InitializeFromConfig(&config);
if (PyStatus_Exception(status)) {
goto exception;
}
PyConfig_Clear(&config);
return;
exception:
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:`Python 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 :ref:`Python UTF-8 Mode <utf8-mode>`
(:pep:`540`) depending on the LC_CTYPE locale, :envvar:`PYTHONUTF8` and
:envvar:`PYTHONCOERCECLOCALE` environment variables.
.. _init-path-config:
Python 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.
See also :c:member:`PyConfig.orig_argv` member.
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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