On Sat, Jun 2, 2018 at 9:02 PM, Steven D'Aprano <steve+comp.lang.pyt...@pearwood.info> wrote: > The violation of reflexivity is weird though :-) > > x = float(NAN) > x == x # returns False > > Don't argue, just accept it :-)
The way I learned it was: there are (of course) a finite number of bit patterns that can represent NaN, but conceptually, there are an infinite number of things that are not numbers, and so two different NaN values could actually represent different non-numbers. Thus, for consistency, we assume that no two non-numbers are equal, regardless of trivial things like bit pattern or identity. (The IEEE standard doesn't have anything about identity, AFAIK, so it's just the bit pattern.) Whether that helps or not is up to you. :) Violating reflexivity truly is weird, especially since some comparisons are described as "x == y" but implemented as "x is y or x == y". But trying to maintain reflexivity would make other things even more weird... ChrisA -- https://mail.python.org/mailman/listinfo/python-list
