According to PEP3123, all accesses to ob_refcnt and ob_type MUST cast the object pointer to PyObject* (unless the pointer is already known to have that type), and SHOULD use the respective accessor macros.

I find that there are still some macros in Python use (obj)->ob_type. Though right now they may not impose any error, but as macros, they may be used with arguments not of type PyObject* later and introduce errors. So I think change them to use Py_TYPE is not a bad idea.