Message 170946 - Python tracker

Terry: can you propose an alternative wording? I don't think that the discussion of TypeError belongs into the description of NotImplemented, though.

IIUC, NotImplemented was added for performance reasons; returning a value is much faster than raising an exception. The return only requires an INCREF/DECREF pair, and a pointer identity test. The exception requires to create a new object, possibly a traceback, and a subclass check on exception matching.