Guido van Rossum wrote:
> On 3/6/06, Raymond Hettinger <[EMAIL PROTECTED]> wrote:
>> [Neil Schemenauer]
>>> I occasionally need dictionaries or sets that use object identity
>>> rather than __hash__ to store items. Would it be appropriate to add
>>> these to the collections module?
>> Why not decorate the objects with a class adding a method:
>> def __hash__(self):
>> return id(self)
>>
>> That would seem to be more Pythonic than creating custom variants of other
>> containers.
>
> I hate to second-guess the OP, but you'd have to override __eq__ too,
> and probably __ne__ and __cmp__ just to be sure. And probably that
> wouldn't do -- since the default __hash__ and __eq__ have the desired
> behavior, the OP is apparently talking about objects that override
> these operations to do something meaningful; overriding them back
> presumably breaks other functionality.
>
> I wonder if this use case and the frequently requested
> case-insensitive dict don't have some kind of generalization in common
> -- perhaps a dict that takes a key function a la list.sort()?
That's what occurred to me as soon as I read Neil's post as well. I
think it would have the added benefit that it would be case insensitive
while still preserving case. Here's a rough idea of the semantics:
from UserDict import DictMixin
class KeyedDict(DictMixin):
def __init__(self, keyfunc):
self.keyfunc = keyfunc
self.data = {}
def __getitem__(self, key):
return self.data[self.keyfunc(key)][1]
def __setitem__(self, key, value):
self.data[self.keyfunc(key)] = (key, value)
def __delitem__(self, key):
del self.data[self.keyfunc(key)]
def keys(self):
return [v[0] for v in self.data.values()]
I definitely like this more than a key-normalizing dictionary -- the
normalized key is never actually exposed anywhere. I didn't follow the
defaultdict thing through to the end, so I didn't catch what the
constructor was going to look like for that; but I assume those choices
will apply here as well.
--
Ian Bicking | [EMAIL PROTECTED] | http://blog.ianbicking.org
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