[Python-Dev] Proposal: defaultdict

Fredrik Lundh fredrik at pythonware.com
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...)


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