On Aug 21, 1:13 pm, Nicholas Cole <nicholas.c...@gmail.com> wrote: > I've searched for information on this without success. Has > weakref.proxy changed in Python 3? I couldn't see any note in the > documentation, but the following code behaves differently on Python > 2.6.1 and Python 3: > > import weakref > class Test(object): pass > > realobject = Test() > pobject = weakref.proxy(realobject) > l = [pobject,] > > print(realobject in l) # On python 2.6 this prints False, on Python 3 True.
So the change underlying what you're seeing is that comparisons in 3.x 'unwrap' the proxy, while in 2.x they don't: 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 It looks to me as though this could be a long-standing defect in Python 2.x, unwittingly(?) corrected in Python 3.x when 3-way comparisons were removed in favour of rich comparisons. See http://svn.python.org/view?view=rev&revision=51533 For 2.7, the proxy source (in Objects/weakrefobject.c) defines a 'proxy_compare' function that's used in the 'tp_compare' slot for proxy objects, and that proxy_compare function has code to unwrap the proxy objects when necessary so that comparisons are done on the real underlying objects. *But* C-level tp_compare slots only ever get called when both objects have the same type, so when comparing a real object with the proxy for that object, that's never. In 3.x, that's replace with a proxy_richcompare function for the tp_richcompare slot. So my guess is that the change was unintentional. It's probably worth a bug report. Even if the behaviour isn't going to change in either 2.x or 3.x (and it probably isn't), it might be possible to clarify the docs. -- Mark -- http://mail.python.org/mailman/listinfo/python-list
