best practices: is collections.defaultdict my friend or not?

Pete Emerson pemerson at gmail.com
Sat Mar 6 03:30:47 CET 2010


On Mar 5, 6:10 pm, Andreas Waldenburger <use... at geekmail.INVALID>
wrote:
> On Fri, 5 Mar 2010 17:22:14 -0800 (PST) Pete Emerson
>
>
>
>
>
> <pemer... at gmail.com> wrote:
> > [snip]
> > >>> data['one'] = {}
> > >>> data['one']['two'] = 'three'
> > >>> print data
> > {'one': {'two': 'three'}}
>
> > And through some research, I discovered collections.defaultdict (new
> > in Python 2.5, FWIW):
>
> > >>> import collections
> > >>> data = collections.defaultdict(dict)
> > >>> data['one']['two'] = 'three'
> > >>> print data
> > defaultdict(<type 'dict'>, {'one': {'two': 'three'}})
>
> > [snip]
> > Your thoughts and comments are very much appreciated. I think my brain
> > already knows some of the answers, but my heart ... well, perl and I
> > go way back. Loving python so far, though.
>
> Oh, by the way: That defaultdict route is a pretty solid solution. Not
> sure what problem you're trying to solve -- depending on your usecase,
> there might be a better approach.
>
> If you're just asking hypothetically and you're trying to apply a
> Perl idiom to Python, there probably *is* a better solution.
>
> /W
>
> --
> INVALID? DE!

I found out about the need to declare the higher level as I was
reading in a JSON struct into a dict and then adding a new entry at a
lower level. Mostly just proof of concept stuff as I'm learning
python. I'm not sure that the use of defaultdict is really warranted
for me anywhere just yet. Mostly, I don't want to convert my perl to
python, that seems very counterproductive. Thank you very much for
your insight.

I was a little frightened of doing "import this" ("Hey, kid, run rm -
rf / and see what happens!"), but did, and the words are wise. :)

Pete



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