The details can be different. For example:

>>> 1 .__add__(x=2)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: wrapper __add__ doesn't take keyword arguments

The message contains the word "wrapper" and doesn't contains parenthesis. I think it can be extended for containing the type name ("int.__add__()" or "wrapper __add__ of in objects"), and this hard to do with general _PyErr_NoKeywords(). Let first unify messages, then try to add more useful information in messages and create a general API if this is possible.