[Python-Dev] function for counting items in a sequence

[Brett Cannon]

On 4/7/07, Steven Bethard <steven.bethard at gmail.com> wrote:
>
> On 4/7/07, Steven Bethard <steven.bethard at gmail.com> wrote:
> > Here's a patch implementing collections.counts() as suggested above:
> >
> >      http://bugs.python.org/1696199
> >
> > Example usage, from the docstring::
> >
> >      >>> items = 'acabbacba'
> >      >>> item_counts = counts(items)
> >      >>> for item in 'abcd':
> >      ...     print item, item_counts[item]
> >      ...
> >      a 4
> >      b 3
> >      c 2
> >      d 0
>
> Guido commented in the tracker that it would be worth discussing
> whether that last item (``item_counts['d']``) should return 0 (as a
> defaultdict would) or raise KeyError (as a dict would).
>
> Anyone have a good motivation for one approach or the other?



I say 0 if it is really meant to represent a count as the absense of
something is 0.  The object returned is being viewed as an object
representing the count of items, not specifically as a dict.

-Brett
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