[Python-bugs-list] [ python-Bugs-660098 ] New style classes and __hash__

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Bugs item #660098, was opened at 2002-12-30 19:39
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Category: None
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Thomas Heller (theller)
Assigned to: Guido van Rossum (gvanrossum)
Summary: New style classes and __hash__

Initial Comment:
New style classes obviously inherit a __hash__ 
implementation from object which returns the id. Per 
default this allows using instances as dictionary keys, 
but usually with the wrong behaviour, because most 
often user classes are mutable, and their contained data 
should be used to calculate the hash value.

IMO one possible solution would be to change 
typeobject.c:object_hash() to raise TypeError, and 
change all the immutable (core) Python objects to use 
_Py_HashPointer in their tp_hash slot.

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>Comment By: Thomas Heller (theller)
Date: 2002-12-30 19:50

Message:
Logged In: YES 
user_id=11105

You mean at the end of the inherit_slots() function?
For my extension which I'm currently debugging, tp_compare, 
tp_richcompare, and tp_hash are inherited from base, but 
only tp_hash is != NULL there.

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Comment By: Guido van Rossum (gvanrossum)
Date: 2002-12-30 19:44

Message:
Logged In: YES 
user_id=6380

There seems to be code that tries to inherit tp_hash only
when tp_compare and tp_richcompare are also inherited, but
it seems to be failing.

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