Python/initconfig.c

cpython 3.14 @ ab2d84fe1023/Python/initconfig.c ↗

Python/initconfig.c owns interpreter startup configuration. It parses environment variables (PYTHONPATH, PYTHONDONTWRITEBYTECODE, etc.), command-line flags (-O, -W, -X), and the computed paths (sys.path, sys.prefix) into a PyConfig struct, then passes that struct to Py_InitializeFromConfig.

Map

Lines	Symbol	Role
1-300	PyConfig defaults, PyConfig_InitPythonConfig	Zero config struct with sane defaults
301-700	Environment variable parsing	PYTHONPATH, PYTHONINSPECT, PYTHONOPTIMIZE, etc.
701-1200	Command-line parsing	-c, -m, -W, -X flags
1201-1800	_PyConfig_InitPathConfig	sys.prefix, sys.exec_prefix, sys.path computation
1801-3200	Py_InitializeFromConfig	Drive full interpreter initialization sequence

Reading

PyConfig struct (selected fields)

// CPython: Include/cpython/initconfig.h (used by initconfig.c)
typedef struct {
    int isolated;
    int use_environment;
    int dev_mode;
    int optimization_level;      /* -O flag count */
    int verbose;
    wchar_t *program_name;
    PyWideStringList argv;
    PyWideStringList xoptions;   /* -X options */
    PyWideStringList warnoptions;/* -W options */
    wchar_t *pythonpath_env;     /* PYTHONPATH */
    int write_bytecode;
    ...
} PyConfig;

sys.path computation

_PyConfig_InitPathConfig calls _PyPathConfig_ComputeSysPath0 to find the script directory and _PyGetPath to compute the initial sys.path from PYTHONPATH, the installation prefix, and zipimport paths. This is the most platform-dependent part of initialization.

-X options

-X dev enables development mode (extra assertions, tracemalloc). -X faulthandler installs the fault handler. -X importtime measures import times. These are parsed from config.xoptions and applied during Py_InitializeFromConfig.

Py_InitializeFromConfig sequence

1. Apply PyConfig settings to the interpreter state.
2. Initialize types (_PyTypes_Init).
3. Initialize builtins (_PyBuiltins_Init).
4. Initialize sys module.
5. Initialize importlib and frozen modules.
6. Set sys.path.

gopy notes

gopy initializes via pythonrun/runstring.go and the stdlibinit registry. There is no PyConfig struct; configuration is passed as Go arguments to the run function. sys.path is a static list of built-in module names since path-based import is not yet implemented.