Stéphane Wirtel: "In fact, _Py_ctype_table is limited to the internal parts of the interpreter. So in this case, this one could not be used in an external tool. You can read: https://docs.python.org/3/c-api/stable.html"

You're right that pyctype.h is excluded from the limited C API. But almost all C extensions use the "regular" C API which includes header files in Include/cpython/.

The internal C API is something different: header files in Include/internal/.

I know that it's complicated, that why a README was written :-)
https://github.com/python/cpython/blob/master/Include/README.rst