cpython/Include/cpython/import.h

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

PyMODINIT_FUNC PyInit__imp(void);

struct _inittab { … };
// This is not used after Py_Initialize() is called.
PyAPI_DATA(struct _inittab *) PyImport_Inittab;
PyAPI_FUNC(int) PyImport_ExtendInittab(struct _inittab *newtab);

struct _frozen { … };

/* Embedding apps may change this pointer to point to their favorite
   collection of frozen modules: */

PyAPI_DATA(const struct _frozen *) PyImport_FrozenModules;