assymetry between a == b and a.__eq__(b) (WAS: pre-PEP genericobjects)
steven.bethard at gmail.com
Wed Dec 1 22:13:24 CET 2004
Terry Reedy wrote:
> "Steven Bethard" <steven.bethard at gmail.com> wrote in message
> >>>def __eq__(self, other):
>>>> """x.__eq__(y) <==> x == y"""
>>>> return (isinstance(other, self.__class__)
> Since an instance of a subclass is an instance of a parent class, but not
> vice versa, I believe you introduce here the assymetry you verify below.
Yes, the asymmetry is due to isinstance.
I believe what Peter Otten was pointing out is that calling __eq__ is
not the same as using ==, presumably because the code for == checks the
types of the two objects and returns False if they're different before
the __eq__ code ever gets called.
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