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Groups > comp.lang.python > #69845

Re: Keeping track of things with dictionaries

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"Chris Angelico" <rosuav@gmail.com> wrote in message 
news:CAPTjJmpK-rqX0fp6_4vXYUS2Z34Vc5fQ_qNTj+Q9+Kn8Y5UPAA@mail.gmail.com...
> On Tue, Apr 8, 2014 at 5:14 PM, Frank Millman <frank@chagford.com> wrote:
>> It appears that when you use 'setdefault', the default is always 
>> evaluated,
>> even if the key exists.
>>
>> It seems odd. Is there a situation where this behaviour is useful?
>
> If the default value is cheap to define and has no side effects, it
> can be very clean.
>
> words_by_length = {}
> for word in open("/usr/share/dict/words"):
>    words_by_length.setdefault(len(word), []).append(word)
>
> This will, very conveniently, give you a list of all words of a
> particular length. (It's actually a little buggy but you get the
> idea.)
>

Thanks, that is neat.

I haven't spotted the bug yet! Can you give me a hint?

Frank

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Keeping track of things with dictionaries Giuliano Bertoletti <gbe32241@libero.it> - 2014-04-06 09:44 +0200
  Re: Keeping track of things with dictionaries Peter Otten <__peter__@web.de> - 2014-04-06 10:23 +0200
  Re: Keeping track of things with dictionaries Josh English <Joshua.R.English@gmail.com> - 2014-04-07 21:02 -0700
    Re: Keeping track of things with dictionaries Chris Angelico <rosuav@gmail.com> - 2014-04-08 14:08 +1000
      Re: Keeping track of things with dictionaries Josh English <Joshua.R.English@gmail.com> - 2014-04-07 23:22 -0700
    Re: Keeping track of things with dictionaries "Frank Millman" <frank@chagford.com> - 2014-04-08 09:14 +0200
      Re: Keeping track of things with dictionaries Steven D'Aprano <steve@pearwood.info> - 2014-04-08 07:47 +0000
    Re: Keeping track of things with dictionaries Ian Kelly <ian.g.kelly@gmail.com> - 2014-04-08 01:53 -0600
    Re: Keeping track of things with dictionaries Chris Angelico <rosuav@gmail.com> - 2014-04-08 18:00 +1000
    Re: Keeping track of things with dictionaries Peter Otten <__peter__@web.de> - 2014-04-08 10:21 +0200
    Re: Keeping track of things with dictionaries "Frank Millman" <frank@chagford.com> - 2014-04-08 10:26 +0200
    Re: Keeping track of things with dictionaries "Frank Millman" <frank@chagford.com> - 2014-04-08 10:31 +0200
      Re: Keeping track of things with dictionaries alex23 <wuwei23@gmail.com> - 2014-04-09 12:34 +1000
    Re: Keeping track of things with dictionaries Chris Angelico <rosuav@gmail.com> - 2014-04-08 18:35 +1000
      Re: Keeping track of things with dictionaries Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-04-09 12:43 +1200
        Re: Keeping track of things with dictionaries Chris Angelico <rosuav@gmail.com> - 2014-04-09 12:33 +1000
          Re: Keeping track of things with dictionaries alex23 <wuwei23@gmail.com> - 2014-04-09 12:45 +1000
            Re: Keeping track of things with dictionaries Ian Kelly <ian.g.kelly@gmail.com> - 2014-04-08 21:19 -0600
            Re: Keeping track of things with dictionaries Gene Heskett <gheskett@wdtv.com> - 2014-04-08 23:31 -0400
            Re: Keeping track of things with dictionaries Ian Kelly <ian.g.kelly@gmail.com> - 2014-04-08 21:37 -0600
    Re: Keeping track of things with dictionaries "Frank Millman" <frank@chagford.com> - 2014-04-08 11:28 +0200
    Re: Keeping track of things with dictionaries Chris Angelico <rosuav@gmail.com> - 2014-04-08 19:34 +1000
    Re: Keeping track of things with dictionaries "Frank Millman" <frank@chagford.com> - 2014-04-08 11:41 +0200
  Re: Keeping track of things with dictionaries Gene Heskett <gheskett@wdtv.com> - 2014-04-09 05:51 -0400

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