[ python-Bugs-1170766 ] weakref.proxy incorrect behaviour

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Bugs item #1170766, was opened at 2005-03-25 16:54
Message generated for change (Comment added) made by rhettinger
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Category: Python Library
Group: Python 2.4
Status: Open
Resolution: None
Priority: 5
Submitted By: Alexander Kozlovsky (kozlovsky)
Assigned to: Nobody/Anonymous (nobody)
Summary: weakref.proxy incorrect behaviour

Initial Comment:
According documentation, proxy in most contexts must 
have the same behaviour as object itself.

PROBLEM:

bool(proxy_object) != bool(object_itself)

EXAMPLE:

>>> class X(list): pass # collection class
... 
>>> x = X() # empty collection
>>> import weakref
>>> proxy = weakref.proxy(x)
>>> bool(x)
False
>>> bool(proxy)
True

PYTHON VERSION:

2.4 (#60, Nov 30 2004, 11:49:19) [MSC v.1310 32 bit 
(Intel)]

also tested on:

2.3.4 (#53, May 25 2004, 21:17:02) [MSC v.1200 32 bit 
(Intel)]

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>Comment By: Raymond Hettinger (rhettinger)
Date: 2005-03-27 06:17

Message:
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Fixed the __nonzero__ problem for Py2.5 and will backport to
Py2.4.  See Objects/weakrefobject.c 1.21.

Leaviing this report open until the rest of the module can
be checked and fixed.



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Comment By: Armin Rigo (arigo)
Date: 2005-03-26 09:50

Message:
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The bug is in weakrefobject:proxy_nonzero(), which calls the underlying object's nb_nonzero slot instead of going through the general PyObject_IsTrue() mecanism.  Built-in types like list and dict don't have a nb_nonzero slot.

As a related bug, (Callable)ProxyType should implement tp_richcompare in addition to tp_compare.  In fact, we should review the code to check if ProxyType knows about the most recent type slots...

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