Python Initialization Configuration

New in version 3.8.

Structures:

PyConfig
PyPreConfig
PyStatus
PyWideStringList

Functions:

The preconfiguration (PyPreConfig type) is stored in _PyRuntime.preconfig and the configuration (PyConfig type) is stored in PyInterpreterState.config.

PyWideStringList

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

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.

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

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:

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 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): 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.

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 to 0.

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.

int coerce_c_locale_warn: If non-zero, emit a warning if the C locale is coerced.

int dev_mode: See PyConfig.dev_mode.

int isolated: See PyConfig.isolated.

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.

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.

int use_environment: See PyConfig.use_environment.

int utf8_mode: If non-zero, enable the UTF-8 mode.

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.