[Python-Dev] == on object tests identity in 3.x

Anders J. Munch 2014 at jmunch.dk
Tue Jul 8 22:10:59 CEST 2014


Steven D'Aprano wrote:

> - Dropping reflexivity preserves the useful property that NANs compare
>    unequal to everything.

Please present an example from real life where that turned out useful, and earn 
yourself a beer!
I've only experienced examples to the contrary.

> - Keeping reflexivity for NANs would have implied some pretty nasty
>    things, e.g. if log(-3) == log(-5), then -3 == -5.

 >>> log(-3)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ValueError: math domain error

You were perhaps referring to the log functions in C and Fortran, not math.log?
The tradeoffs are different in those languages, so choices the IEEE-754 
committee made with C and Fortran in mind may be less relevant for Python.

regards, Anders




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