[Python-Dev] collections.idset and collections.iddict?

Guido van Rossum guido at python.org
Tue Mar 7 01:14:54 CET 2006

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()?

--Guido van Rossum (home page: http://www.python.org/~guido/)

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