[Python-Dev] Why is nan != nan? (original) (raw)

Alexander Belopolsky alexander.belopolsky at gmail.com
Wed Mar 24 23:36:49 CET 2010


On Wed, Mar 24, 2010 at 6:31 PM, Mark Dickinson <dickinsm at gmail.com> wrote: ..

Neither is necessary, because Python doesn't actually use == as the equivalence relation for containment testing:  the actual equivalence relation is:  x equivalent to y iff id(x) == id(y) or x == y.  This restores the missing reflexivity (besides being a useful optimization).

No, it does not:

float('nan') in [float('nan')] False

It would if NaNs were always interned, but they are not.



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