On Sep 28, 2005, at 9:12 AM, Reinhold Birkenfeld wrote: > Hi, > > a general question. Consider: > > class A(list): > def __setitem__(self, index, item): > # do something with index and item > return list.__setitem__(self, index, item) > > lst = A([1,set()]) > > lst[0] |= 1 > > lst[1] |= set([1]) > > Do we want lst.__setitem__ to be called in the second inplace > assignment?
Yes. Right now, you can roughly explain the behavior by stating that, after "x=a", "x |= y" is the same as "x = x | y", except that "a"'s value is undefined (it might have changed, or it might have not). > A case where this matters is here: http://python.org/sf/1306777 This confusion between modification of immutable types and modification of mutable types is why I feel that it's often best to simply avoid the inplace operators in favor of their explicit equivalents. In this case, set.update(). James _______________________________________________ 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
