On Tue, Jul 8, 2014 at 12:54 PM, Anders J. Munch <2...@jmunch.dk> wrote: > > Ian Kelly wrote: >> >> As far as I know nothing changed between 2.4 and 2.7 in this regard. >> Python has always had NaN compare unequal to everything, per the >> standard. > > It might have been platform-specific in 2.4.
I doubt it, but okay, which platform? >> Okay, here's your problem: there isn't just one binary representation >> for NaN. > > I'm fully aware of that. Whether NaN's are one equivalence class or several > is not the issue. What matters is the integrity of the equivalence relation. I have some bad news for you. This is on Python 2.7.6: >>> from decimal import Decimal >>> from fractions import Fraction >>> Decimal(2) == 2 True >>> 2 == Fraction(2) True >>> Decimal(2) == Fraction(2) False I'm not sure exactly when this bug was fixed, but it works as expected in 3.4.0. >> Following the standard isn't a good reason itself? > > If a standard tells you to jump of a cliff... So I don't know of a good use case for nan != nan in Python (but really I'm not the one to ask), but I do know of use cases in other scenarios. On platforms that don't provide an isnan() function, the only convenient and efficient way to test for nan is by testing reflexivity: x != x. Following the standard means that any algorithm that uses this trick can (in theory) be implemented in Python without changes. -- https://mail.python.org/mailman/listinfo/python-list
