# Configuração de Inicialização do Python

Novo na versão 3.8.

Estruturas:

- `PyConfig`

- `PyPreConfig`

- `PyStatus`

- `PyWideStringList`

Funções:

- `PyConfig_Clear()`

- `PyConfig_InitIsolatedConfig()`

- `PyConfig_InitPythonConfig()`

- `PyConfig_Read()`

- `PyConfig_SetArgv()`

- `PyConfig_SetBytesArgv()`

- `PyConfig_SetBytesString()`

- `PyConfig_SetString()`

- `PyConfig_SetWideStringList()`

- `PyPreConfig_InitIsolatedConfig()`

- `PyPreConfig_InitPythonConfig()`

- `PyStatus_Error()`

- `PyStatus_Exception()`

- `PyStatus_Exit()`

- `PyStatus_IsError()`

- `PyStatus_IsExit()`

- `PyStatus_NoMemory()`

- `PyStatus_Ok()`

- `PyWideStringList_Append()`

- `PyWideStringList_Insert()`

- `Py_ExitStatusException()`

- `Py_InitializeFromConfig()`

- `Py_PreInitialize()`

- `Py_PreInitializeFromArgs()`

- `Py_PreInitializeFromBytesArgs()`

- `Py_RunMain()`

A pré-configuração (tipo `PyPreConfig`) é armazenado em `_PyRuntime.preconfig` e a configuração (tipo `PyConfig`) é armazenado em `PyInterpreterState.config`.

Veja também Inicialização, Finalização e Threads.

Ver também

PEP 587 “Configuração da inicialização do Python”.

## PyWideStringList

`PyWideStringList`

  Lista de strings `wchar_t*`.

  Se length é diferente de zero, items deve ser diferente de `NULL` e todas as strings devem ser diferentes de `NULL`.

  Métodos:

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

    Anexa item a list.

    Python deve ser inicializado previamente antes de chamar essa função.

  PyStatus `PyWideStringList_Insert`(PyWideStringList *list, Py_ssize_t index, const wchar_t *item)

    Insere item na list na posição index.

    Se index for maior ou igual ao comprimento da list, anexa o item a list.

    index deve ser maior que ou igual a 0.

    Python deve ser inicializado previamente antes de chamar essa função.

  Campos de estrutura

  Py_ssize_t `length`

    Comprimento da lista.

  wchar_t** `items`

    Itens da lista.

## PyStatus

`PyStatus`

  Estrutura para armazenar o status de uma função de inicialização: sucesso, erro ou saída.

  Para um erro, ela pode armazenar o nome da função C que criou o erro.

  Campos de estrutura

  int `exitcode`

    Código de saída. Argumento passado para `exit()`.

  const char *`err_msg`

    Mensagem de erro.

  const char *`func`

    Nome da função que criou um erro. Pode ser `NULL`.

  Funções para criar um status:

  PyStatus `PyStatus_Ok`(void)

    Sucesso.

  PyStatus `PyStatus_Error`(const char *err_msg)

    Erro de inicialização com uma mensagem.

  PyStatus `PyStatus_NoMemory`(void)

    Falha de alocação de memória (sem memória).

  PyStatus `PyStatus_Exit`(int exitcode)

    Sai do Python com o código de saída especificado.

  Funções para manipular um status:

  int `PyStatus_Exception`(PyStatus status)

    O status é um erro ou uma saída? Se verdadeiro, a exceção deve ser tratada; chamando `Py_ExitStatusException()`, por exemplo.

  int `PyStatus_IsError`(PyStatus status)

    O resultado é um erro?

  int `PyStatus_IsExit`(PyStatus status)

    O resultado é uma saída?

  void `Py_ExitStatusException`(PyStatus status)

    Chama `exit(exitcode)` se status for uma saída. Exibe a mensagem de erro e sai com um código de saída diferente de zero se status for um erro. Deve ser chamado apenas se `PyStatus_Exception(status)` for diferente de zero.

Nota

Internamente, Python usa macros que definem `PyStatus.func`, enquanto funções para criar um status definem `func` para `NULL`.

Exemplo:

    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

`PyPreConfig`

  Estrutura usada para pré-inicializar o Python:

  - Define o alocador de memória do Python

  - Configura a localidade LC_CTYPE

  - Define o modo UTF-8

  A função para inicializar uma pré-configuração:

  void `PyPreConfig_InitPythonConfig`(PyPreConfig *preconfig)

    Inicializa a pré-configuração com Configuração do Python.

  void `PyPreConfig_InitIsolatedConfig`(PyPreConfig *preconfig)

    Inicializa a pré-configuração com Configuração isolada.

  Campos de estrutura

  int `allocator`

    Nome do alocador de memória:

    - `PYMEM_ALLOCATOR_NOT_SET` (`0`): não altera os alocadores de memória (usa o padrão)

    - `PYMEM_ALLOCATOR_DEFAULT` (`1`): alocadores de memória padrão

    - `PYMEM_ALLOCATOR_DEBUG` (`2`): alocadores de memória padrão com ganchos de depuração

    - `PYMEM_ALLOCATOR_MALLOC` (`3`): força o uso de `malloc()`

    - `PYMEM_ALLOCATOR_MALLOC_DEBUG` (`4`): força o uso de `malloc()` com ganchos de depuração

    - `PYMEM_ALLOCATOR_PYMALLOC` (`5`): Alocador de memória do Python pymalloc

    - `PYMEM_ALLOCATOR_PYMALLOC_DEBUG` (`6`): alocador de memória do Python pymalloc com ganchos de depuração

    `PYMEM_ALLOCATOR_PYMALLOC` e `PYMEM_ALLOCATOR_PYMALLOC_DEBUG` não são suportados se Python estiver configurado usando `--without-pymalloc`

    Veja Gerenciamento de memória.

  int `configure_locale`

    Definir a localidade LC_CTYPE para a localidade preferida do usuário? Se for igual a 0, define `coerce_c_locale` e `coerce_c_locale_warn` para 0.

  int `coerce_c_locale`

    Se for igual a 2, força a localidade C; se for igual a 1, lê a localidade LC_CTYPE para decidir se deve ser forçado.

  int `coerce_c_locale_warn`

    Se diferente de zero, emite um aviso se a localidade C for forçada.

  int `dev_mode`

    Veja `PyConfig.dev_mode`.

  int `isolated`

    Veja `PyConfig.isolated`.

  int `legacy_windows_fs_encoding`(Windows only)

    Se diferente de zero, desabilita o modo UTF-8, define a codificação do sistema de arquivos Python para `mbcs`, define o tratador de erros do sistema de arquivos para `replace`.

    Disponível apenas no Windows. A macro `#ifdef MS_WINDOWS` pode ser usada para código específico do Windows.

  int `parse_argv`

    Se diferente de zero, `Py_PreInitializeFromArgs()` e `Py_PreInitializeFromBytesArgs()` analisam seu argumento `argv` da mesma forma que o Python regular analisa argumentos de linha de comando: vej Argumentos de linha de comando.

  int `use_environment`

    Veja `PyConfig.use_environment`.

  int `utf8_mode`

    Se não zero, habilita o modo UTF-8.

## Preinitialization with PyPreConfig

Functions to preinitialize Python:

PyStatus `Py_PreInitialize`(const PyPreConfig *preconfig)

  Preinitialize Python from preconfig preconfiguration.

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

  Preinitialize Python from preconfig preconfiguration and command line arguments (bytes strings).

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 `PyStatus_Exception()` and `Py_ExitStatusException()`.

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

`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 Python preinitialization, whereas calling directly `malloc()` and `free()` is always safe. `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

`PyConfig`

  Structure containing most parameters to configure Python.

  Structure methods:

  void `PyConfig_InitPythonConfig`(PyConfig *config)

    Initialize configuration with Python Configuration.

  void `PyConfig_InitIsolatedConfig`(PyConfig *config)

    Initialize configuration with Isolated Configuration.

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

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

    Preinitialize Python if needed.

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

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

    Preinitialize Python if needed.

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

    Set command line arguments from wide character strings.

    Preinitialize Python if needed.

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

    Set command line arguments: decode bytes using `Py_DecodeLocale()`.

    Preinitialize Python if needed.

  PyStatus `PyConfig_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.

    Preinitialize Python if needed.

  void `PyConfig_Clear`(PyConfig *config)

    Release configuration memory.

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

  - `dev_mode`

  - `isolated`

  - `parse_argv`

  - `use_environment`

  Moreover, if `PyConfig_SetArgv()` or `PyConfig_SetBytesArgv()` is used, this method must be called first, before other methods, since the preinitialization configuration depends on command line arguments (if `parse_argv` is non-zero).

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

  Campos de estrutura

  PyWideStringList `argv`

    Command line arguments, `sys.argv`. See `parse_argv` to parse `argv` the same way the regular Python parses Python command line arguments. If `argv` is empty, an empty string is added to ensure that `sys.argv` always exists and is never empty.

  wchar_t* `base_exec_prefix`

    `sys.base_exec_prefix`.

  wchar_t* `base_executable`

    `sys._base_executable`: `__PYVENV_LAUNCHER__` environment variable value, or copy of `PyConfig.executable`.

  wchar_t* `base_prefix`

    `sys.base_prefix`.

  int `buffered_stdio`

    If equals to 0, enable unbuffered mode, making the stdout and stderr streams unbuffered.

    stdin is always opened in buffered mode.

  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.

  wchar_t* `check_hash_pycs_mode`

    Control the validation behavior of hash-based `.pyc` files (see PEP 552): `--check-hash-based-pycs` command line option value.

    Valid values: `always`, `never` and `default`.

    The default value is: `default`.

  int `configure_c_stdio`

    If non-zero, configure C standard streams (`stdio`, `stdout`, `stdout`). For example, set their mode to `O_BINARY` on Windows.

  int `dev_mode`

    Development mode: see `-X dev`.

  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).

  wchar_t* `exec_prefix`

    `sys.exec_prefix`.

  wchar_t* `executable`

    `sys.executable`.

  int `faulthandler`

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

  wchar_t* `filesystem_encoding`

    Filesystem encoding, `sys.getfilesystemencoding()`.

  wchar_t* `filesystem_errors`

    Filesystem encoding errors, `sys.getfilesystemencodeerrors()`.

  unsigned long `hash_seed`
  int `use_hash_seed`

    Randomized hash function seed.

    If `use_hash_seed` is zero, a seed is chosen randomly at Pythonstartup, and `hash_seed` is ignored.

  wchar_t* `home`

    Python home directory.

    Initialized from `PYTHONHOME` environment variable value by default.

  int `import_time`

    If non-zero, profile import time.

  int `inspect`

    Enter interactive mode after executing a script or a command.

  int `install_signal_handlers`

    Install signal handlers?

  int `interactive`

    Interactive mode.

  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.

  int `legacy_windows_stdio`

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

    Disponível apenas no Windows. A macro `#ifdef MS_WINDOWS` pode ser usada para código específico do Windows.

  int `malloc_stats`

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

    The option is ignored if Python is built using `--without-pymalloc`.

  wchar_t* `pythonpath_env`

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

    Initialized from `PYTHONPATH` environment variable value by default.

  PyWideStringList `module_search_paths`
  int `module_search_paths_set`

    `sys.path`. If `module_search_paths_set` is equal to 0, the `module_search_paths` is overridden by the function calculating the Path Configuration.

  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

  int `parse_argv`

    If non-zero, parse `argv` the same way the regular Python command line arguments, and strip Python arguments from `argv`: see Command Line Arguments.

  int `parser_debug`

    If non-zero, turn on parser debugging output (for expert only, depending on compilation options).

  int `pathconfig_warnings`

    If equal to 0, suppress warnings when calculating the Path Configuration (Unix only, Windows does not log any warning). Otherwise, warnings are written into `stderr`.

  wchar_t* `prefix`

    `sys.prefix`.

  wchar_t* `program_name`

    Program name. Used to initialize `executable`, and in early error messages.

  wchar_t* `pycache_prefix`

    `sys.pycache_prefix`: `.pyc` cache prefix.

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

  int `quiet`

    Quiet mode. For example, don’t display the copyright and version messages in interactive mode.

  wchar_t* `run_command`

    `python3 -c COMMAND` argument. Used by `Py_RunMain()`.

  wchar_t* `run_filename`

    `python3 FILENAME` argument. Used by `Py_RunMain()`.

  wchar_t* `run_module`

    `python3 -m MODULE` argument. Used by `Py_RunMain()`.

  int `show_alloc_count`

    Show allocation counts at exit?

    Set to 1 by `-X showalloccount` command line option.

    Need a special Python build with `COUNT_ALLOCS` macro defined.

  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 (`Py_REF_DEBUG` macro must be defined).

  int `site_import`

    Import the `site` module at startup?

  int `skip_source_first_line`

    Skip the first line of the source?

  wchar_t* `stdio_encoding`
  wchar_t* `stdio_errors`

    Encoding and encoding errors of `sys.stdin`, `sys.stdout` and `sys.stderr`.

  int `tracemalloc`

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

  int `use_environment`

    If greater than 0, use environment variables.

  int `user_site_directory`

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

  int `verbose`

    If non-zero, enable verbose mode.

  PyWideStringList `warnoptions`

    `sys.warnoptions`: options of the `warnings` module to build warnings filters: lowest to highest priority.

    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).

  int `write_bytecode`

    If non-zero, write `.pyc` files.

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

  PyWideStringList `xoptions`

    `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 Command Line Arguments.

The `xoptions` options are parsed to set other options: see `-X` option.

## 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.

Example setting the program name:

    void init_python(void)
    {
        PyStatus status;

        PyConfig config;
        PyConfig_InitPythonConfig(&config);

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

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

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

More complete example modifying the default configuration, read the configuration, and then override some parameters:

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

        PyConfig config;
        PyConfig_InitPythonConfig(&config);

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

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

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

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

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

        status = Py_InitializeFromConfig(&config);

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

## Isolated Configuration

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

This configuration ignores global configuration variables, environments variables, 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 Path Configuration (“output fields”) to ignore these configuration files and avoid the function computing the default path configuration.

## Configuração do Python

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

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

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

Exemplo de Python personalizado rodando sempre em um modo isolado:

    int main(int argc, char **argv)
    {
        PyStatus status;

        PyConfig config;
        PyConfig_InitPythonConfig(&config);
        config.isolated = 1;

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

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

        return Py_RunMain();

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

## Path Configuration

`PyConfig` contains multiple fields for the path configuration:

- Path configuration inputs:

  - `PyConfig.home`

  - `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()`.

## Multi-Phase Initialization Private Provisional API

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

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

  - Builtin types;

  - Builtin exceptions;

  - Builtin and frozen modules;

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

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

  - Install and configure `importlib`;

  - Apply the Path Configuration;

  - Install signal handlers;

  - Finish `sys` module initialization (ex: create `sys.stdout` and `sys.path`);

  - Enable optional features like `faulthandler` and `tracemalloc`;

  - Import the `site` module;

  - etc.

Private provisional API:

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

PyStatus `_Py_InitializeMain`(void)

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

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

It may become possible to 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);
        }
    }