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[Python-Dev] Counter proposal: multidict (was: Proposal: defaultdict)

Jack Diederich jack at performancedrivers.com
Fri Feb 17 21:25:14 CET 2006 
On Fri, Feb 17, 2006 at 03:03:06PM -0500, Fred L. Drake, Jr. wrote:
> On Friday 17 February 2006 14:51, Ian Bicking wrote:
>  > and in the process breaking an important 
>  > quality of good Python code, that attribute and getitem access not have
>  > noticeable side effects.
> 
> I'm not sure that's quite as well-defined or agreed upon as you do.
 
Without the __getitem__ side effect default objects that don't support any
operators would have problems.

  d[key] += val

works fine when the default is a list or int but fails for dicts and presumably
many user defined objects.  By assigning the default value in __getitem__ the
returned value can be manipulated via its methods.

-Jack
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