[ python-Bugs-1730322 ] getattr([], '__eq__')(some-object) is NotImplemented

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Bugs item #1730322, was opened at 2007-06-03 13:10
Message generated for change (Comment added) made by collinwinter
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Category: Type/class unification
Group: Python 2.5
>Status: Closed
>Resolution: Wont Fix
Priority: 5
Private: No
Submitted By: L. Peter Deutsch (lpd)
Assigned to: Nobody/Anonymous (nobody)
Summary: getattr([], '__eq__')(some-object) is NotImplemented

Initial Comment:
Consider:

a = []

class B: pass

class C(object): pass

print a == B()

print a == C()

m = getattr(a, '__eq__')

print m(B())

print m(C())

I think this should print 'False' 4 times, but it actually prints:

False
False
NotImplemented
NotImplemented

If this isn't a bug, please explain why.


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>Comment By: Collin Winter (collinwinter)
Date: 2007-06-05 14:23

Message:
Logged In: YES 
user_id=1344176
Originator: NO

This isn't a bug because a.__eq__() isn't the whole story on equivalence
testing. NotImplemented is a perfectly valid return value for a comparison
method; in this case, it signals the == operator to try a different
approach.

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