"Guido van Rossum" <[EMAIL PROTECTED]> 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/
_______________________________________________
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
