On Sat, Sep 13, 2008 at 1:20 PM, Armin Ronacher <[EMAIL PROTECTED]> wrote: > Hi everybody, > > In Python 2.x when iterating over a weak key dictionary for example, the > common > idom for doing that was calling dictionary.keys() to ensure that a list of all > objects is returned it was safe to iterate over as a weak reference could stop > existing during dict iteration which of course raises a runtime error by the > dict iterator. > > This was documented behavior and worked pretty well, with the small problem > that > suddenly all references in the dict wouldn't die until iteration is over > because > the list holds references to the object. > > This no longer works in Python 3 because .keys() on the weak key dictionary > returns a generator over the key view of the internal dict which of course has > the same problem as iterkeys in Python 2.x. > > The following code shows the problem:: > > from weakref import WeakKeyDictionary > > f1 = Foo() > f2 = Foo() > d = WeakKeyDictionary() > d[f1] = 42 > d[f2] = 23 > > i = iter(d.keys()) # or use d.keyrefs() here which has the same problem > print(next(i)) > del f2 > print(next(i)) > > This example essentially dies with "RuntimeError: dictionary changed > size during iteration" as soon as f2 is deleted. > > Iterating over weak key dictionaries might not be the most common task but I > know some situations where this is necessary. Unfortunately I can't see a > way to achieve that in Python 3.
i = list(d.keys()) - Josiah _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
