Interpreter initialization and finalization

See Python Initialization Configuration for details on how to configure the interpreter prior to initialization.

Before Python initialization

In an application embedding Python, the Py_Initialize() function must be called before using any other Python/C API functions; with the exception of a few functions and the global configuration variables.

The following functions can be safely called before Python is initialized:

• Functions that initialize the interpreter:

  • Py_Initialize()

  • Py_InitializeEx()

  • Py_InitializeFromConfig()

  • Py_BytesMain()

  • Py_Main()

  • the runtime pre-initialization functions covered in Python Initialization Configuration

• Configuration functions:

  • PyImport_AppendInittab()

  • PyImport_ExtendInittab()

  • PyInitFrozenExtensions()

  • PyMem_SetAllocator()

  • PyMem_SetupDebugHooks()

  • PyObject_SetArenaAllocator()

  • Py_SetProgramName()

  • Py_SetPythonHome()

  • the configuration functions covered in Python Initialization Configuration

• Informative functions:

  • Py_IsInitialized()

  • PyMem_GetAllocator()

  • PyObject_GetArenaAllocator()

  • Py_GetBuildInfo()

  • Py_GetCompiler()

  • Py_GetCopyright()

  • Py_GetPlatform()

  • Py_GetVersion()

  • Py_IsInitialized()

• Utilities:

  • Py_DecodeLocale()

  • the status reporting and utility functions covered in Python Initialization Configuration

• Memory allocators:

  • PyMem_RawMalloc()

  • PyMem_RawRealloc()

  • PyMem_RawCalloc()

  • PyMem_RawFree()

• Synchronization:

  • PyMutex_Lock()

  • PyMutex_Unlock()

Note

Despite their apparent similarity to some of the functions listed above, the following functions should not be called before the interpreter has been initialized: Py_EncodeLocale(), PyEval_InitThreads(), and Py_RunMain().

Global configuration variables

Python has variables for the global configuration to control different features and options. By default, these flags are controlled by command line options.

When a flag is set by an option, the value of the flag is the number of times that the option was set. For example, -b sets Py_BytesWarningFlag to 1 and -bb sets Py_BytesWarningFlag to 2.

int Py_BytesWarningFlag

This API is kept for backward compatibility: setting PyConfig.bytes_warning should be used instead, see Python Initialization Configuration.

Issue a warning when comparing bytes or bytearray with str or bytes with int. Issue an error if greater or equal to 2.

Set by the -b option.

Deprecated since version 3.12, will be removed in version 3.15.

int Py_DebugFlag

This API is kept for backward compatibility: setting PyConfig.parser_debug should be used instead, see Python Initialization Configuration.

Turn on parser debugging output (for expert only, depending on compilation options).

Set by the -d option and the PYTHONDEBUG environment variable.

Deprecated since version 3.12, will be removed in version 3.15.

int Py_DontWriteBytecodeFlag

This API is kept for backward compatibility: setting PyConfig.write_bytecode should be used instead, see Python Initialization Configuration.

If set to non-zero, Python won’t try to write .pyc files on the import of source modules.

Set by the -B option and the PYTHONDONTWRITEBYTECODE environment variable.

Deprecated since version 3.12, will be removed in version 3.15.

int Py_FrozenFlag

This API is kept for backward compatibility: setting PyConfig.pathconfig_warnings should be used instead, see Python Initialization Configuration.

Private flag used by _freeze_module and frozenmain programs.