New submission from Mark Dickinson <dicki...@gmail.com>: Nicholas Cole noted on python-list that the behaviour of weakref.proxy with respect to equality changed between 2.x and 3.x:
Python 2.7 (r27:82500, Aug 15 2010, 14:21:15) [GCC 4.2.1 (Apple Inc. build 5664)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> import weakref >>> s = set() >>> s == weakref.proxy(s) False Python 3.1.2 (r312:79147, Aug 20 2010, 20:06:00) [GCC 4.2.1 (Apple Inc. build 5664)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> import weakref >>> s = set() >>> s == weakref.proxy(s) True This seems to be an inadvertent change resulting from the switch from 3-way comparisons to rich comparisons: the 2.x source implements tp_compare for proxy objects. The tp_compare slot *does* unwrap the proxy objects before comparing, but since the tp_compare slot in general is only ever called (for objects implemented in C) when the types of the objects being compared are the same, a proxy object won't compare equal to its referent. I believe that Nicholas ran into this when using weakrefs as elements of containers. Nicholas: is that right? Care to elaborate? The 3.x source changes this to use tp_richcompare (see r51533), so now a proxy object *does* compare equal to its referent. The 3.x behaviour seems better to my limited eyes, and the 2.x behaviour has been around a long time without causing problems, so we probably don't want to change the behaviour in either case. But it might be good to document the difference somewhere. ---------- messages: 114557 nosy: mark.dickinson priority: normal severity: normal status: open title: weakref.proxy unequal to its referent in 2.x type: behavior versions: Python 2.6, Python 2.7 _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue9658> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
