Path: csiph.com!v102.xanadu-bbs.net!xanadu-bbs.net!feeder.erje.net!eu.feeder.erje.net!xlned.com!feeder3.xlned.com!newsfeed.xs4all.nl!newsfeed2a.news.xs4all.nl!xs4all!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail
Return-Path: <python-python-list@m.gmane.org>
X-Original-To: python-list@python.org
Delivered-To: python-list@mail.python.org
X-Spam-Status: OK 0.002
X-Spam-Evidence: '*H*': 1.00; '*S*': 0.00; 'exists.': 0.07; 'clean.': 0.09; 'received:80.91': 0.09; 'received:80.91.229': 0.09; 'received:gmane.org': 0.09; 'received:list': 0.09; 'will,': 0.09; 'bug': 0.12; 'wrote': 0.14; "(it's": 0.16; 'buggy': 0.16; 'hint?': 0.16; 'length.': 0.16; 'received:80.91.229.3': 0.16; 'received:plane.gmane.org': 0.16; 'skip:n 70': 0.16; 'spotted': 0.16; 'subject:dictionaries': 0.16; 'thanks,': 0.17; 'wrote:': 0.18; 'cheap': 0.19; 'seems': 0.21; 'appears': 0.22; "haven't": 0.24; 'define': 0.26; 'header:X-Complaints-To:1': 0.27; 'words': 0.29; "skip:' 10": 0.31; 'subject:with': 0.35; 'but': 0.35; 'there': 0.35; 'list': 0.37; 'skip:[ 10': 0.38; 'to:addr:python- list': 0.38; 'pm,': 0.38; 'little': 0.38; 'to:addr:python.org': 0.39; 'received:org': 0.40; 'even': 0.60; 'skip:o 30': 0.61; 'situation': 0.65; 'side': 0.67; 'frank': 0.68; 'skip:w 30': 0.69; 'default': 0.69; 'effects,': 0.84
X-Injected-Via-Gmane: http://gmane.org/
To: python-list@python.org
From: "Frank Millman" <frank@chagford.com>
Subject: Re: Keeping track of things with dictionaries
Date: Tue, 8 Apr 2014 10:26:27 +0200
References: <534105ce$0$1365$4fafbaef@reader1.news.tin.it> <21ef5159-ad95-4d43-a2d6-7ecda941d978@googlegroups.com> <CAPTjJmqFBt2XX+BDfNHz0gaGOrDkhtpBzrR29DUWN36girzcSw@mail.gmail.com> <li07kt$4cl$1@ger.gmane.org> <CAPTjJmpK-rqX0fp6_4vXYUS2Z34Vc5fQ_qNTj+Q9+Kn8Y5UPAA@mail.gmail.com>
X-Gmane-NNTP-Posting-Host: 197.87.50.147
X-MSMail-Priority: Normal
X-Newsreader: Microsoft Outlook Express 6.00.3790.4657
X-RFC2646: Format=Flowed; Original
X-MimeOLE: Produced By Microsoft MimeOLE V6.00.3790.4913
X-BeenThere: python-list@python.org
X-Mailman-Version: 2.1.15
Precedence: list
List-Id: General discussion list for the Python programming language <python-list.python.org>
List-Unsubscribe: <https://mail.python.org/mailman/options/python-list>, <mailto:python-list-request@python.org?subject=unsubscribe>
List-Archive: <http://mail.python.org/pipermail/python-list/>
List-Post: <mailto:python-list@python.org>
List-Help: <mailto:python-list-request@python.org?subject=help>
List-Subscribe: <https://mail.python.org/mailman/listinfo/python-list>, <mailto:python-list-request@python.org?subject=subscribe>
Newsgroups: comp.lang.python
Message-ID: <mailman.9002.1396945603.18130.python-list@python.org>
Lines: 30
NNTP-Posting-Host: 2001:888:2000:d::a6
X-Trace: 1396945603 news.xs4all.nl 2936 [2001:888:2000:d::a6]:34657
X-Complaints-To: abuse@xs4all.nl
Xref: csiph.com comp.lang.python:69845


"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