"Guido van Rossum" <guido@python.org> writes:
If the __getattr__()-like operation that supplies and inserts a dynamic default was a separate method, we wouldn't have this problem.
Why implement it in the dictionary type at all? If, for intance, the default value functionality were provided as a decorator, it could be used with all kinds of mappings. I.e. you could have something along these lines: class defaultwrapper(object): def __init__(self, base, factory): self.__base = base self.__factory = factory def __getitem__(self, key): try: return self.__base[key] except KeyError: value = self.__factory() self.__base[key] = value return value def __getattr__(self, attr): return getattr(self.__base, attr) def test(): dd = defaultwrapper({}, list) dd["abc"].append(1) dd["abc"].append(2) dd["def"].append(1) assert sorted(dd.keys()) == ["abc", "def"] assert sorted(dd.values()) == [[1], [1, 2]] assert sorted(dd.items()) == [("abc", [1, 2]), ("def", [1])] assert dd.has_key("abc") assert not dd.has_key("xyz") The precise semantics would have to be determined yet, of course.
OTOH most reviewers here seem to appreciate on_missing() as a way to do various other ways of alterning a dict's __getitem__() behavior behind a caller's back -- perhaps it could even be (ab)used to implement case-insensitive lookup.
case-insensitive lookup could be implemented with another wrapper/decorator. If you need both case-insitivity and a default value, you can easily stack the decorators. Bernhard -- Intevation GmbH http://intevation.de/ Skencil http://skencil.org/ Thuban http://thuban.intevation.org/