include/python3.9/internal/pycore_abstract.h

#ifndef Py_INTERNAL_ABSTRACT_H
#define Py_INTERNAL_ABSTRACT_H
#ifdef __cplusplus
extern "C" {
#endif

#ifndef Py_BUILD_CORE
#  error "this header requires Py_BUILD_CORE define"
#endif

// Fast inlined version of PyIndex_Check()
static inline int
_PyIndex_Check(PyObject *obj)
{
    PyNumberMethods *tp_as_number = Py_TYPE(obj)->tp_as_number;
    return (tp_as_number != NULL && tp_as_number->nb_index != NULL);
}

#ifdef __cplusplus
}
#endif
#endif /* !Py_INTERNAL_ABSTRACT_H */