[Python-Dev] Proposal: defaultdict

Fri Feb 17 12:14:27 CET 2006

Guido van Rossum wrote:
> A bunch of Googlers were discussing the best way of doing the
> following (a common idiom when maintaining a dict of lists of values
> relating to a key, sometimes called a multimap):
>> if key not in d: d[key] = []
> d[key].append(value)

/.../
> Feedback?

+1. check it in, already (as collections.defaultdict, perhaps?)
alternatively, you could specialize even further: collections.multimap,
which deals with list values only (that shallow copy thing feels a bit
questionable, but all alternatives feel slightly overgeneralized...)
</F>