[docs] [issue15997] NotImplemented needs to be documented

Terry J. Reedy report at bugs.python.org
Sat Sep 22 02:10:49 CEST 2012

Terry J. Reedy added the comment:

The first three sentences are fine. The problem I have is with the 4th: 'may return' is rather vague. Such methods may raise TypeError instead (the old way), seemingly to the same effect. (See msg170936 in issue #12067, which is about clarifying the comparisons section of the expression chapter.). So the 5th sentence could be misinterpreted wrongly to mean that NotImplemented is needed to get the alternate method try. (Since it is not, I wonder why it was added, since it complicates the internal logic of arithmetic and comparison ops.)

Perhaps a better place for any clarification on this point would be in 3.3 in the entry for __le__, etc.

nosy: +terry.reedy

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