On Tue, Sep 22, 2015 at 9:47 AM, Tim Peters <tim.pet...@gmail.com> wrote:
> [Tim] > >>> ... > >>> The > >>> top-level operation on the RHS is datetime.fromtimestamp(). However, > >>> it didn't pass a tzinfo, so it creates a naive datetime. Assuming dt > >>> was aware to begin with, the attempt to compare will always (gap or > >>> not) raise an exception. > > [Tim] > >> Oops! In current Python, comparing naive and aware via `==` just > >> returns False. That's even more confusing ;-) > > [Guido] > > Hm, but that's in general how == is *supposed* to work between objects of > > incompatible types. < and > are supposed to fail but == is supposed to > > return False (the __eq__ should return NotImplemented). If == ever > raises an > > exception, having two different objects as dict keys can cause random, > > hard-to-debug failures. > > Sure - no complaint. I was just saying that in the specific, > complicated, contrived expression Nick presented, that it always > returns False (no matter which aware datetime he starts with) would be > more of a head-scratcher than if it raised a "can't compare naive and > aware datetimes" exception instead. > And yet I think the desired behavior of == requires us to return False. I think we should change this in the PEP, except I can't find where the PEP says == should raise an exception in this case. > That's why, whenever anyone is confused by anything they see in a > Python program, they should post all their code verbatim to > Python-Dev, prefaced with a "Doesn't work! Fix it." comment ;-) > Oh, it would be so much better if they posted their code! -- --Guido van Rossum (python.org/~guido)
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