Python Initialization Configuration
***********************************

New in version 3.8.

Python can be initialized with "Py_InitializeFromConfig()" and the
"PyConfig" structure. It can be preinitialized with
"Py_PreInitialize()" and the "PyPreConfig" structure.

There are two kinds of configuration:

* The Python Configuration can be used to build a customized Python
  which behaves as the regular Python. For example, environment
  variables and command line arguments are used to configure Python.

* The Isolated Configuration can be used to embed Python into an
  application. It isolates Python from the system. For example,
  environment variables are ignored, the LC_CTYPE locale is left
  unchanged and no signal handler is registered.

The "Py_RunMain()" function can be used to write a customized Python
program.

See also Initialization, Finalization, and Threads.

See also: **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
================

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:

   PyStatus PyWideStringList_Append(PyWideStringList *list, const wchar_t *item)

      Append *item* to *list*.

      Python must be preinitialized to call this 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:

   Py_ssize_t length

      List length.

   wchar_t **items

      List items.


PyStatus
========

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:

   int exitcode

      Exit code. Argument passed to "exit()".

   const char *err_msg

      Error message.

   const char *func

      Name of the function which created an error, can be "NULL".

   Functions to create a status:

   PyStatus PyStatus_Ok(void)

      Success.

   PyStatus PyStatus_Error(const char *err_msg)

      Initialization error with a message.

      *err_msg* must not be "NULL".

   PyStatus PyStatus_NoMemory(void)

      Memory allocation failure (out of memory).

   PyStatus PyStatus_Exit(int exitcode)

      Exit Python with the specified exit code.

   Functions to handle a status:

   int PyStatus_Exception(PyStatus status)

      Is the status an error or an exit? If true, the exception must
      be handled; by calling "Py_ExitStatusException()" for example.

   int PyStatus_IsError(PyStatus status)

      Is the result an error?

   int PyStatus_IsExit(PyStatus status)

      Is the result an exit?

   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
===========

type PyPreConfig

   Structure used to preinitialize Python.

   Function to initialize a preconfiguration:

   void PyPreConfig_InitPythonConfig(PyPreConfig *preconfig)

      Initialize the preconfiguration with Python Configuration.

   void PyPreConfig_InitIsolatedConfig(PyPreConfig *preconfig)

      Initialize the preconfiguration with Isolated Configuration.

   Structure fields:

   int allocator

      Name of the Python memory allocators:

      * "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"): use "malloc()" of the C
        library.

      * "PYMEM_ALLOCATOR_MALLOC_DEBUG" ("4"): force usage of
        "malloc()" with debug hooks.

      * "PYMEM_ALLOCATOR_PYMALLOC" ("5"): Python pymalloc memory
        allocator.

      * "PYMEM_ALLOCATOR_PYMALLOC_DEBUG" ("6"): 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 Memory Management.

      Default: "PYMEM_ALLOCATOR_NOT_SET".

   int configure_locale

      Set the LC_CTYPE locale to the user preferred locale.

      If equals to 0, set "coerce_c_locale" and "coerce_c_locale_warn"
      members to 0.

      See the *locale encoding*.

      Default: "1" in Python config, "0" in isolated config.

   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 *locale encoding*.

      Default: "-1" in Python config, "0" in isolated config.

   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.

   int dev_mode

      If non-zero, enables the Python Development Mode: see
      "PyConfig.dev_mode".

      Default: "-1" in Python mode, "0" in isolated mode.

   int isolated

      Isolated mode: see "PyConfig.isolated".

      Default: "0" in Python mode, "1" in isolated mode.

   int legacy_windows_fs_encoding

      If non-zero:

      * Set "PyPreConfig.utf8_mode" to "0",

      * Set "PyConfig.filesystem_encoding" to ""mbcs"",

      * Set "PyConfig.filesystem_errors" to ""replace"".

      Initialized the from "PYTHONLEGACYWINDOWSFSENCODING" environment
      variable value.

      Only available on Windows. "#ifdef MS_WINDOWS" macro can be used
      for Windows specific code.

      Default: "0".

   int parse_argv

      If non-zero, "Py_PreInitializeFromArgs()" and
      "Py_PreInitializeFromBytesArgs()" parse their "argv" argument
      the same way the regular Python parses command line arguments:
      see Command Line Arguments.

      Default: "1" in Python config, "0" in isolated config.

   int use_environment

      Use environment variables? See "PyConfig.use_environment".

      Default: "1" in Python config and "0" in isolated config.

   int utf8_mode

      If non-zero, enable the Python UTF-8 Mode.

      Set by the "-X utf8" command line option and the "PYTHONUTF8"
      environment variable.

      Default: "-1" in Python config and "0" in isolated config.


Preinitialize Python with PyPreConfig
=====================================

The preinitialization of Python:

* Set the Python memory allocators ("PyPreConfig.allocator")

* Configure the LC_CTYPE locale (*locale encoding*)

* Set the Python UTF-8 Mode ("PyPreConfig.utf8_mode")

The current preconfiguration ("PyPreConfig" type) is stored in
"_PyRuntime.preconfig".

Functions to preinitialize Python:

PyStatus Py_PreInitialize(const PyPreConfig *preconfig)

   Preinitialize Python from *preconfig* preconfiguration.

   *preconfig* must not be "NULL".

PyStatus Py_PreInitializeFromBytesArgs(const PyPreConfig *preconfig, int argc, char *const *argv)

   Preinitialize Python from *preconfig* preconfiguration.

   Parse *argv* command line arguments (bytes strings) if "parse_argv"
   of *preconfig* is non-zero.

   *preconfig* must not be "NULL".

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 "parse_argv"
   of *preconfig* is non-zero.

   *preconfig* must not be "NULL".

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

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

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

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

Example using the preinitialization to enable the Python 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 speaks UTF-8 */

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


PyConfig
========

type PyConfig

   Structure containing most parameters to configure Python.

   When done, the "PyConfig_Clear()" function must be used to release
   the configuration memory.

   Structure methods:

   void PyConfig_InitPythonConfig(PyConfig *config)

      Initialize configuration with the Python Configuration.

   void PyConfig_InitIsolatedConfig(PyConfig *config)

      Initialize configuration with the Isolated Configuration.

   PyStatus PyConfig_SetString(PyConfig *config, wchar_t *const *config_str, const wchar_t *str)

      Copy the wide character string *str* into "*config_str".

      Preinitialize Python if needed.

   PyStatus PyConfig_SetBytesString(PyConfig *config, wchar_t *const *config_str, const char *str)

      Decode *str* using "Py_DecodeLocale()" and set the result into
      "*config_str".

      Preinitialize Python if needed.

   PyStatus PyConfig_SetArgv(PyConfig *config, int argc, wchar_t *const *argv)

      Set command line arguments ("argv" member of *config*) from the
      *argv* list of wide character strings.

      Preinitialize Python if needed.

   PyStatus PyConfig_SetBytesArgv(PyConfig *config, int argc, char *const *argv)

      Set command line arguments ("argv" member of *config*) from the
      *argv* list of bytes strings. Decode bytes using
      "Py_DecodeLocale()".

      Preinitialize Python if needed.

   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.

   PyStatus PyConfig_Read(PyConfig *config)

      Read all Python configuration.

      Fields which are already initialized are left unchanged.

      The "PyConfig_Read()" function only parses "PyConfig.argv"
      arguments once: "PyConfig.parse_argv" is set to "2" after
      arguments are parsed. Since Python arguments are strippped from
      "PyConfig.argv", parsing arguments twice would parse the
      application options as Python options.

      Preinitialize Python if needed.

      Changed in version 3.10: The "PyConfig.argv" arguments are now
      only parsed once, "PyConfig.parse_argv" is set to "2" after
      arguments are parsed, and arguments are only parsed if
      "PyConfig.parse_argv" equals "1".

   void PyConfig_Clear(PyConfig *config)

      Release configuration memory.

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

   * "PyConfig.dev_mode"

   * "PyConfig.isolated"

   * "PyConfig.parse_argv"

   * "PyConfig.use_environment"

   Moreover, if "PyConfig_SetArgv()" or "PyConfig_SetBytesArgv()" is
   used, this method must be called before other methods, since the
   preinitialization configuration depends on command line arguments
   (if "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:

   PyWideStringList argv

      Command line arguments: "sys.argv".

      Set "parse_argv" to "1" to parse "argv" the same way the regular
      Python parses Python command line arguments and then to strip
      Python arguments from "argv".

      If "argv" is empty, an empty string is added to ensure that
      "sys.argv" always exists and is never empty.

      Default: "NULL".

      See also the "orig_argv" member.

   wchar_t *base_exec_prefix

      "sys.base_exec_prefix".

      Default: "NULL".

      Part of the Python Path Configuration output.

   wchar_t *base_executable

      Python base executable: "sys._base_executable".

      Set by the "__PYVENV_LAUNCHER__" environment variable.

      Set from "PyConfig.executable" if "NULL".

      Default: "NULL".

      Part of the Python Path Configuration output.

   wchar_t *base_prefix

      "sys.base_prefix".

      Default: "NULL".

      Part of the Python Path Configuration output.

   int buffered_stdio

      If equals to 0 and "configure_c_stdio" is non-zero, disable
      buffering on the C streams stdout and stderr.

      Set to 0 by the "-u" command line option and the
      "PYTHONUNBUFFERED" environment variable.

      stdin is always opened in buffered mode.

      Default: "1".

   int bytes_warning

      If equals to 1, issue a warning when comparing "bytes" or
      "bytearray" with "str", or comparing "bytes" with "int".

      If equal or greater to 2, raise a "BytesWarning" exception in
      these cases.

      Incremented by the "-b" command line option.

      Default: "0".

   int warn_default_encoding

      If non-zero, emit a "EncodingWarning" warning when
      "io.TextIOWrapper" uses its default encoding. See Opt-in
      EncodingWarning for details.

      Default: "0".

      New in version 3.10.

   wchar_t *check_hash_pycs_mode

      Control the validation behavior of hash-based ".pyc" files:
      value of the "--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”.

   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 "buffered_stdio" equals zero, disable buffering of stdin,
        stdout and stderr streams.

      * If "interactive" is non-zero, enable stream buffering on stdin
        and stdout (only stdout on Windows).

      Default: "1" in Python config, "0" in isolated config.

   int dev_mode

      If non-zero, enable the Python Development Mode.

      Default: "-1" in Python mode, "0" in isolated mode.

   int dump_refs

      Dump Python references?

      If non-zero, dump all objects which are still alive at exit.

      Set to "1" by the "PYTHONDUMPREFS" environment variable.

      Need a special build of Python with the "Py_TRACE_REFS" macro
      defined: see the "configure --with-trace-refs option".

      Default: "0".

   wchar_t *exec_prefix

      The site-specific directory prefix where the platform-dependent
      Python files are installed: "sys.exec_prefix".

      Default: "NULL".

      Part of the Python Path Configuration output.

   wchar_t *executable

      The absolute path of the executable binary for the Python
      interpreter: "sys.executable".

      Default: "NULL".

      Part of the Python Path Configuration output.

   int faulthandler

      Enable faulthandler?

      If non-zero, call "faulthandler.enable()" at startup.

      Set to "1" by "-X faulthandler" and the "PYTHONFAULTHANDLER"
      environment variable.

      Default: "-1" in Python mode, "0" in isolated mode.

   wchar_t *filesystem_encoding

      *Filesystem encoding*: "sys.getfilesystemencoding()".

      On macOS, Android and VxWorks: use ""utf-8"" by default.

      On Windows: use ""utf-8"" by default, or ""mbcs"" if
      "legacy_windows_fs_encoding" of "PyPreConfig" is non-zero.

      Default encoding on other platforms:

      * ""utf-8"" if "PyPreConfig.utf8_mode" is non-zero.

      * ""ascii"" if Python detects that "nl_langinfo(CODESET)"
        announces the ASCII encoding, whereas the "mbstowcs()"
        function decodes from a different encoding (usually Latin1).

      * ""utf-8"" if "nl_langinfo(CODESET)" returns an empty string.

      * Otherwise, use the *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 "filesystem_errors" member.

   wchar_t *filesystem_errors

      *Filesystem error handler*: "sys.getfilesystemencodeerrors()".

      On Windows: use ""surrogatepass"" by default, or ""replace""  if
      "legacy_windows_fs_encoding" of "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 "filesystem_encoding" member.

   unsigned long hash_seed

   int use_hash_seed

      Randomized hash function seed.

      If "use_hash_seed" is zero, a seed is chosen randomly at Python
      startup, and "hash_seed" is ignored.

      Set by the "PYTHONHASHSEED" environment variable.

      Default *use_hash_seed* value: "-1" in Python mode, "0" in
      isolated mode.

   wchar_t *home

      Python home directory.

      If "Py_SetPythonHome()" has been called, use its argument if it
      is not "NULL".

      Set by the "PYTHONHOME" environment variable.

      Default: "NULL".

      Part of the Python Path Configuration input.

   int import_time

      If non-zero, profile import time.

      Set the "1" by the "-X importtime" option and the
      "PYTHONPROFILEIMPORTTIME" environment variable.

      Default: "0".

   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 "sys.stdin"
      does not appear to be a terminal.

      Incremented by the "-i" command line option. Set to "1" if the
      "PYTHONINSPECT" environment variable is non-empty.

      Default: "0".

   int install_signal_handlers

      Install Python signal handlers?

      Default: "1" in Python mode, "0" in isolated mode.

   int interactive

      If greater than 0, enable the interactive mode (REPL).

      Incremented by the "-i" command line option.

      Default: "0".

   int isolated

      If greater than 0, enable isolated mode:

      * "sys.path" contains neither the script’s directory (computed
        from "argv[0]" or the current directory) nor the user’s site-
        packages directory.

      * Python REPL doesn’t import "readline" nor enable default
        readline configuration on interactive prompts.

      * Set "use_environment" and "user_site_directory" to 0.

      Default: "0" in Python mode, "1" in isolated mode.

      See also "PyPreConfig.isolated".

   int legacy_windows_stdio

      If non-zero, use "io.FileIO" instead of "io.WindowsConsoleIO"
      for "sys.stdin", "sys.stdout" and "sys.stderr".

      Set to "1" if the "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).

   int malloc_stats

      If non-zero, dump statistics on Python pymalloc memory allocator
      at exit.

      Set to "1" by the "PYTHONMALLOCSTATS" environment variable.

      The option is ignored if Python is "configured using the
      --without-pymalloc option".

      Default: "0".

   wchar_t *platlibdir

      Platform library directory name: "sys.platlibdir".

      Set by the "PYTHONPLATLIBDIR" environment variable.

      Default: value of the "PLATLIBDIR" macro which is set by the
      "configure --with-platlibdir option" (default: ""lib"").

      Part of the Python Path Configuration input.

      New in version 3.9.

   wchar_t *pythonpath_env

      Module search paths ("sys.path") as a string separated by
      "DELIM" ("os.path.pathsep").

      Set by the "PYTHONPATH" environment variable.

      Default: "NULL".

      Part of the Python Path Configuration input.

   PyWideStringList module_search_paths

   int module_search_paths_set

      Module search paths: "sys.path".

      If "module_search_paths_set" is equal to 0, the function
      calculating the Python Path Configuration overrides the
      "module_search_paths" and sets "module_search_paths_set" to "1".

      Default: empty list ("module_search_paths") and "0"
      ("module_search_paths_set").

      Part of the Python Path Configuration output.

   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 "-O" command line option. Set to the
      "PYTHONOPTIMIZE" environment variable value.

      Default: "0".

   PyWideStringList orig_argv

      The list of the original command line arguments passed to the
      Python executable: "sys.orig_argv".

      If "orig_argv" list is empty and "argv" is not a list only
      containing an empty string, "PyConfig_Read()" copies "argv" into
      "orig_argv" before modifying "argv" (if "parse_argv" is non-
      zero).

      See also the "argv" member and the "Py_GetArgcArgv()" function.

      Default: empty list.

      New in version 3.10.

   int parse_argv

      Parse command line arguments?

      If equals to "1", parse "argv" the same way the regular Python
      parses command line arguments, and strip Python arguments from
      "argv".

      The "PyConfig_Read()" function only parses "PyConfig.argv"
      arguments once: "PyConfig.parse_argv" is set to "2" after
      arguments are parsed. Since Python arguments are strippped from
      "PyConfig.argv", parsing arguments twice would parse the
      application options as Python options.

      Default: "1" in Python mode, "0" in isolated mode.

      Changed in version 3.10: The "PyConfig.argv" arguments are now
      only parsed if "PyConfig.parse_argv" equals to "1".

   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 "-d" command line option. Set to the
      "PYTHONDEBUG" environment variable value.

      Default: "0".

   int pathconfig_warnings

      On Unix, if non-zero, calculating the Python Path Configuration
      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 Python Path Configuration input.

   wchar_t *prefix

      The site-specific directory prefix where the platform
      independent Python files are installed: "sys.prefix".

      Default: "NULL".

      Part of the Python Path Configuration output.

   wchar_t *program_name

      Program name used to initialize "executable" and in early error
      messages during Python initialization.

      * If "Py_SetProgramName()" has been called, use its argument.

      * On macOS, use "PYTHONEXECUTABLE" environment variable if set.

      * If the "WITH_NEXT_FRAMEWORK" macro is defined, use
        "__PYVENV_LAUNCHER__" environment variable if set.

      * Use "argv[0]" of "argv" if available and non-empty.

      * Otherwise, use "L"python"" on Windows, or "L"python3"" on
        other platforms.

      Default: "NULL".

      Part of the Python Path Configuration input.

   wchar_t *pycache_prefix

      Directory where cached ".pyc" files are written:
      "sys.pycache_prefix".

      Set by the "-X pycache_prefix=PATH" command line option and the
      "PYTHONPYCACHEPREFIX" environment variable.

      If "NULL", "sys.pycache_prefix" is set to "None".

      Default: "NULL".

   int quiet

      Quiet mode. If greater than 0, don’t display the copyright and
      version at Python startup in interactive mode.

      Incremented by the "-q" command line option.

      Default: "0".

   wchar_t *run_command

      Value of the "-c" command line option.

      Used by "Py_RunMain()".

      Default: "NULL".

   wchar_t *run_filename

      Filename passed on the command line: trailing command line
      argument without "-c" or "-m".

      For example, it is set to "script.py" by the "python3 script.py
      arg" command.

      Used by "Py_RunMain()".

      Default: "NULL".

   wchar_t *run_module

      Value of the "-m" command line option.

      Used by "Py_RunMain()".

      Default: "NULL".

   int show_ref_count

      Show total reference count at exit?

      Set to 1 by "-X showrefcount" command line option.

      Need a debug build of Python (the "Py_REF_DEBUG" macro must be
      defined).

      Default: "0".

   int site_import

      Import the "site" module at startup?

      If equal to zero, disable the import of the module site and the
      site-dependent manipulations of "sys.path" that it entails.

      Also disable these manipulations if the "site" module is
      explicitly imported later (call "site.main()" if you want them
      to be triggered).

      Set to "0" by the "-S" command line option.

      "sys.flags.no_site" is set to the inverted value of
      "site_import".

      Default: "1".

   int skip_source_first_line

      If non-zero, skip the first line of the "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 "-x" command line option.

      Default: "0".

   wchar_t *stdio_encoding

   wchar_t *stdio_errors

      Encoding and encoding errors of "sys.stdin", "sys.stdout" and
      "sys.stderr" (but "sys.stderr" always uses ""backslashreplace""
      error handler).

      If "Py_SetStandardStreamEncoding()" has been called, use its
      *error* and *errors* arguments if they are not "NULL".

      Use the "PYTHONIOENCODING" environment variable if it is non-
      empty.

      Default encoding:

      * ""UTF-8"" if "PyPreConfig.utf8_mode" is non-zero.

      * Otherwise, use the *locale encoding*.

      Default error handler:

      * On Windows: use ""surrogateescape"".

      * ""surrogateescape"" if "PyPreConfig.utf8_mode" is non-zero, or
        if the LC_CTYPE locale is “C” or “POSIX”.

      * ""strict"" otherwise.

   int tracemalloc

      Enable tracemalloc?

      If non-zero, call "tracemalloc.start()" at startup.

      Set by "-X tracemalloc=N" command line option and by the
      "PYTHONTRACEMALLOC" environment variable.

      Default: "-1" in Python mode, "0" in isolated mode.

   int use_environment

      Use environment variables?

      If equals to zero, ignore the environment variables.

      Default: "1" in Python config and "0" in isolated config.

   int user_site_directory

      If non-zero, add the user site directory to "sys.path".

      Set to "0" by the "-s" and "-I" command line options.

      Set to "0" by the "PYTHONNOUSERSITE" environment variable.

      Default: "1" in Python mode, "0" in isolated mode.

   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 "-v" command line option.

      Set to the "PYTHONVERBOSE" environment variable value.

      Default: "0".

   PyWideStringList warnoptions

      Options of the "warnings" module to build warnings filters,
      lowest to highest priority: "sys.warnoptions".

      The "warnings" module adds "sys.warnoptions" in the reverse
      order: the last "PyConfig.warnoptions" item becomes the first
      item of "warnings.filters" which is checked first (highest
      priority).

      The "-W" command line options adds its value to "warnoptions",
      it can be used multiple times.

      The "PYTHONWARNINGS" environment variable can also be used to
      add warning options. Multiple options can be specified,
      separated by commas (",").

      Default: empty list.

   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 "-B" command line option and the
      "PYTHONDONTWRITEBYTECODE" environment variable.

      "sys.dont_write_bytecode" is initialized to the inverted value
      of "write_bytecode".

      Default: "1".

   PyWideStringList xoptions

      Values of the "-X" command line options: "sys._xoptions".

      Default: empty list.

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".

The "xoptions" options are parsed to set other options: see the "-X"
command line option.

Changed in version 3.9: The "show_alloc_count" field has been removed.


Initialization with PyConfig
============================

Function to initialize Python:

PyStatus Py_InitializeFromConfig(const PyConfig *config)

   Initialize Python from *config* configuration.

The caller is responsible to handle exceptions (error or exit) using
"PyStatus_Exception()" and "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. If
Python is initialized multiple times, "PyImport_AppendInittab()" or
"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;
   }


Isolated Configuration
======================

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

This configuration ignores global configuration variables, environment
variables, command line arguments ("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
Python Path Configuration (“output fields”) to ignore these
configuration files and avoid the function computing the default path
configuration.


Python Configuration
====================

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

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

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


Python Path Configuration
=========================

"PyConfig" contains multiple fields for the path configuration:

* Path configuration inputs:

  * "PyConfig.home"

  * "PyConfig.platlibdir"

  * "PyConfig.pathconfig_warnings"

  * "PyConfig.program_name"

  * "PyConfig.pythonpath_env"

  * current working directory: to get absolute paths

  * "PATH" environment variable to get the program full path (from
    "PyConfig.program_name")

  * "__PYVENV_LAUNCHER__" environment variable

  * (Windows only) Application paths in the registry under
    “SoftwarePythonPythonCoreX.YPythonPath” of HKEY_CURRENT_USER and
    HKEY_LOCAL_MACHINE (where X.Y is the Python version).

* Path configuration output fields:

  * "PyConfig.base_exec_prefix"

  * "PyConfig.base_executable"

  * "PyConfig.base_prefix"

  * "PyConfig.exec_prefix"

  * "PyConfig.executable"

  * "PyConfig.module_search_paths_set", "PyConfig.module_search_paths"

  * "PyConfig.prefix"

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

It is possible to completely ignore the function 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 "pathconfig_warnings" to 0 to suppress warnings when calculating
the path configuration (Unix only, Windows does not log any warning).

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

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

* If "run_filename" is set and is a directory which contains a
  "__main__.py" script, prepend "run_filename" to "sys.path".

* If "isolated" is zero:

  * If "run_module" is set, prepend the current directory to
    "sys.path". Do nothing if the current directory cannot be read.

  * If "run_filename" is set, prepend the directory of the filename to
    "sys.path".

  * Otherwise, prepend an empty string to "sys.path".

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

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
"PyConfig.base_executable"


Py_RunMain()
============

int Py_RunMain(void)

   Execute the command ("PyConfig.run_command"), the script
   ("PyConfig.run_filename") or the module ("PyConfig.run_module")
   specified on the command line or in the configuration.

   By default and when if "-i" option is used, run the REPL.

   Finally, finalizes Python and returns an exit status that can be
   passed to the "exit()" function.

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


Py_GetArgcArgv()
================

void Py_GetArgcArgv(int *argc, wchar_t ***argv)

   Get the original command line arguments, before Python modified
   them.

   See also "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 **PEP 432**:

* “Core” initialization phase, “bare minimum Python”:

  * Builtin types;

  * Builtin exceptions;

  * Builtin and frozen modules;

  * The "sys" module is only partially initialized (ex: "sys.path"
    doesn’t exist yet).

* “Main” initialization phase, Python is fully initialized:

  * Install and configure "importlib";

  * Apply the Path Configuration;

  * Install signal handlers;

  * Finish "sys" module initialization (ex: create "sys.stdout" and
    "sys.path");

  * Enable optional features like "faulthandler" and "tracemalloc";

  * Import the "site" module;

  * etc.

Private provisional API:

* "PyConfig._init_main": if set to 0, "Py_InitializeFromConfig()"
  stops at the “Core” initialization phase.

* "PyConfig._isolated_interpreter": if non-zero, disallow threads,
  subprocesses and fork.

PyStatus _Py_InitializeMain(void)

   Move to the “Main” initialization phase, finish the Python
   initialization.

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

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

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

Example running Python code between “Core” and “Main” initialization
phases:

   void init_python(void)
   {
       PyStatus status;

       PyConfig config;
       PyConfig_InitPythonConfig(&config);
       config._init_main = 0;

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

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

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

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

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