cpython/Include/cpython/modsupport.h

#ifndef Py_CPYTHON_MODSUPPORT_H
#  error "this header file must not be included directly"
#endif

// A data structure that can be used to run initialization code once in a
// thread-safe manner. The C++11 equivalent is std::call_once.
typedef struct {
    uint8_t v;
} _PyOnceFlag;

typedef struct _PyArg_Parser {
    const char *format;
    const char * const *keywords;
    const char *fname;
    const char *custom_msg;
    _PyOnceFlag once;       /* atomic one-time initialization flag */
    int is_kwtuple_owned;   /* does this parser own the kwtuple object? */
    int pos;                /* number of positional-only arguments */
    int min;                /* minimal number of arguments */
    int max;                /* maximal number of positional arguments */
    PyObject *kwtuple;      /* tuple of keyword parameter names */
    struct _PyArg_Parser *next;
} _PyArg_Parser;

PyAPI_FUNC(int) _PyArg_ParseTupleAndKeywordsFast(PyObject *, PyObject *,
                                                 struct _PyArg_Parser *, ...);

#ifdef Py_BUILD_CORE
// Internal; defined here to avoid explicitly including pycore_modsupport.h
#define _Py_INTERNAL_ABI_SLOT                             \
    {Py_mod_abi, (void*) &(PyABIInfo) {                   \
        .abiinfo_major_version = 1,                       \
        .abiinfo_minor_version = 0,                       \
        .flags = PyABIInfo_INTERNAL,                      \
        .build_version = PY_VERSION_HEX,                  \
        .abi_version = PY_VERSION_HEX }}                  \
    ///////////////////////////////////////////////////////
#endif