Noam Raphael wrote: > Perhaps it bothers the programmer with something that shouldn't bother > him. I mean that I might do help(set.copy), and then think, "Oh, it > returns a shallow copy. Wait a minute - 'shallow' means that I get a > new object, which references the same objects as the old one. Perhaps > I should use another function, which does deep copying? Let me think > about it - no. All members of a set are immutable, so it doesn't > matter." I think that in this case, the fact that the copy is shallow > is an implementation detail, since there's no sense in making a deep > copy of a set.
If "makes no sense" means "would not make a difference", then you are wrong. Objects in a set are not necessarily unmodifiable; they just have to be hashable. Watch this: >>> class A: ... def __hash__(self):return 0 ... def __cmp__(self, other):return 0 ... >>> a1 = A() >>> import copy >>> a2 = copy.deepcopy(a1) >>> a1.x = 10 >>> a2.x = 20 >>> a1.x 10 >>> s = set([a1]) >>> a2 in s True So even though a1 and a2 are distinct objects with different, modifiable state, they are treated as equal in the set. A deepcopy of the set (if it existed) would do something different than a plain copy. > I know it's just a word, and that it doesn't matter a lot. But why not > make things a tiny bit better? Things would get worse. The code would become underspecified. Regards, Martin _______________________________________________ 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
