[Python-Dev] collections.idset and collections.iddict? (original) (raw)

Bob Ippolito bob at redivi.com
Tue Mar 7 01:43:01 CET 2006

On Mar 6, 2006, at 4:14 PM, Guido van Rossum wrote:

On 3/6/06, Raymond Hettinger <python at rcn.com> 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()?

+1. I've wanted such a thing a couple times, and there is some
precedent in the stdlib (e.g. WeakKeyDictionary would be a lot
shorter with such a base class).

-bob

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