[docs] [issue15997] NotImplemented needs to be documented

Martin v. Löwis report at bugs.python.org
Sat Sep 22 03:12:05 CEST 2012

Martin v. Löwis added the comment:

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.


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