> Since _PyDict_GetItem_KnownHash() may or may not set an exception, we have to check for a live exception after calling it, and that finds the old exception of the last attribute lookup and decides that its own lookup failed.

Hmm, with PyDict_GetItem() we don't falsely detect a lookup failing with a live exception set. Is it correct to call _PyType_Lookup() with an exception set? Perhaps we should save a current exception before calling find_name_in_mro() and restore it after. Or raise SystemError if an exception set. Or just add assert(!PyErr_Occurred()) at the begin of find_name_in_mro(). I don't know what is more correct.