.. 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` 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 `. .. 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_InitIsolatedConfig(PyPreConfig *preconfig) Initialize the preconfiguration with :ref:`Python Configuration `. .. c:function:: void PyPreConfig_InitPythonConfig(PyPreConfig *preconfig) Initialize the preconfiguration with :ref:`Isolated Configuration `. 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 ` * ``PYMEM_ALLOCATOR_PYMALLOC_DEBUG`` (``6``): :ref:`Python pymalloc memory allocator ` 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 `. .. 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 `. .. 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 ` (: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:: PyStatus PyConfig_InitPythonConfig(PyConfig *config) Initialize configuration with :ref:`Python Configuration `. .. c:function:: PyStatus PyConfig_InitIsolatedConfig(PyConfig *config) Initialize configuration with :ref:`Isolated Configuration `. .. 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:: 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 Development mode: see :option:`-X dev <-X>`. .. c:member:: int dump_refs If non-zero, dump all objects which are still alive at exit. Require a debug build of Python (``Py_REF_DEBUG`` macro must be defined). .. 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 ` 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 `. .. 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 `. .. 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 ` (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_alloc_count Show allocation counts at exit? Set to 1 by :option:`-X showalloccount <-X>` command line option. Need a special Python build with ``COUNT_ALLOCS`` macro defined. .. 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 `. .. 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`. 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 `. The ``xoptions`` options are parsed to set other options: see :option:`-X` option. 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 ``PyImport_FrozenModules``, ``PyImport_AppendInittab()`` or ``PyImport_ExtendInittab()`` are used, they must be set or called after Python preinitialization and before the Python initialization. Example setting the program name:: void init_python(void) { PyStatus status; PyConfig config; status = PyConfig_InitPythonConfig(&config); if (PyStatus_Exception(status)) { goto fail; } /* 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; status = PyConfig_InitPythonConfig(&config); if (PyStatus_Exception(status)) { goto done; } /* Set the program name before reading the configuraton (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 ` ("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; status = PyConfig_InitPythonConfig(&config); if (PyStatus_Exception(status)) { goto fail; } 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.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 ` for an example of customized Python always running in isolated mode using :c:func:`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 :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 `; * 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: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 ` is only applied during the "Main" phase. It may allow to customize Python in Python to override or tune the :ref:`Path Configuration `, maybe install a custom :data:`sys.meta_path` importer or an import hook, etc. It may become possible to calculatin the :ref:`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; status = PyConfig_InitPythonConfig(&config); if (PyStatus_Exception(status)) { PyConfig_Clear(&config); Py_ExitStatusException(status); } 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); } }