[issue2235] __eq__ / __hash__ check doesn't take inheritance into account

[Nick Coghlan]

Nick Coghlan <ncoghlan at gmail.com> added the comment:

As far as deque goes, the following behaviour on the trunk is the
problem I am trying to fix:

Python 2.6b1+ (trunk:64655, Jul  2 2008, 22:48:24)
[GCC 4.1.3 20070929 (prerelease) (Ubuntu 4.1.2-16ubuntu2)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from collections import deque, Hashable
>>> isinstance(deque(), Hashable)
True

All of the container types that my patch touches were already unhashable
in 2.5 - my patch just ensures that they all correctly return false for
isinstance(obj, collections.Hashable) even after we make object.__hash__
inherited by default again. This is also the reason why simply reverting
the trunk hash implementation to the 2.5 behaviour (which is what I
first tried) is inadequate.

Since collections.Hashable is new in 2.6, I can live with it returning
the wrong answer for types which define __hash__ to always raise an
error (that's a known limitation of the ABC system, even in Py3k).
However, we should at least make sure it returns the correct answer for
all of the types in the standard library.

----------
assignee:  -> ncoghlan

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue2235>
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