Path: csiph.com!x330-a1.tempe.blueboxinc.net!usenet.pasdenom.info!gegeweb.org!de-l.enfer-du-nord.net!feeder1.enfer-du-nord.net!tudelft.nl!txtfeed1.tudelft.nl!multikabel.net!newsfeed20.multikabel.net!news2.euro.net!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail Return-Path: X-Original-To: python-list@python.org Delivered-To: python-list@mail.python.org X-Spam-Status: OK 0.000 X-Spam-Evidence: '*H*': 1.00; '*S*': 0.00; 'python.': 0.04; 'context': 0.04; 'implements': 0.05; 'example)': 0.07; 'space.': 0.07; 'type,': 0.07; 'python': 0.08; '>>>>': 0.09; 'received:80.91': 0.09; 'received:80.91.229': 0.09; 'received:gmane.org': 0.09; 'received:list': 0.09; '"copyright",': 0.16; '"credits"': 0.16; '"license"': 0.16; '[])': 0.16; '[gcc': 0.16; 'from:addr:behnel.de': 0.16; 'from:addr:stefan_ml': 0.16; 'from:name:stefan behnel': 0.16; 'subject:() ': 0.16; 'subject:sum': 0.16; 'language': 0.16; 'meant': 0.17; 'wrote:': 0.18; 'subject:not': 0.19; "doesn't": 0.22; 'appropriate': 0.22; 'header:In-Reply-To:1': 0.22; 'feb': 0.22; 'elements': 0.24; 'specify': 0.24; 'stefan': 0.24; 'lists': 0.28; 'class': 0.29; 'pm,': 0.29; 'can.': 0.30; 'mentioning': 0.30; 'subject:number': 0.30; '(the': 0.30; 'chris': 0.30; 'creates': 0.31; 'thu,': 0.32; 'list': 0.32; 'implement': 0.32; 'initial': 0.32; 'there': 0.33; 'header:User-Agent:1': 0.33; 'it.': 0.33; 'header:X-Complaints- To:1': 0.34; 'received:84': 0.34; 'certain': 0.34; 'to:addr :python-list': 0.35; 'copying': 0.35; 'two': 0.36; 'received:org': 0.36; 'example,': 0.37; 'but': 0.37; 'machine': 0.37; 'should': 0.38; 'third': 0.38; 'to:addr:python.org': 0.40; 'type': 0.61; 'more': 0.61; 'worth': 0.61; 'design': 0.61; 'efficient': 0.62; '"sum': 0.84; '(based': 0.84; '2.7.1': 0.84; '4.2.1': 0.84; 'buck': 0.84; 'involved.': 0.91; 'jul': 0.93 X-Injected-Via-Gmane: http://gmane.org/ To: python-list@python.org From: Stefan Behnel Subject: Re: sum() requires number, not simply __add__ Date: Thu, 23 Feb 2012 22:42:22 +0100 References: <91c71e41-b98c-46f6-b3af-bed894cf9d92@kh11g2000pbb.googlegroups.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Gmane-NNTP-Posting-Host: dslb-084-056-059-089.pools.arcor-ip.net User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.2) Gecko/20120216 Thunderbird/10.0.2 In-Reply-To: X-BeenThere: python-list@python.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: General discussion list for the Python programming language List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Newsgroups: comp.lang.python Message-ID: Lines: 27 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1330033355 news.xs4all.nl 6854 [2001:888:2000:d::a6]:51173 X-Complaints-To: abuse@xs4all.nl Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:20754 Chris Rebert, 23.02.2012 22:32: > On Thu, Feb 23, 2012 at 1:19 PM, Buck Golemon wrote: >> I feel like the design of sum() is inconsistent with other language >> features of python. Often python doesn't require a specific type, only >> that the type implement certain methods. >> >> Given a class that implements __add__ why should sum() not be able to >> operate on that class? > > The time machine strikes again! sum() already can. You just need to > specify an appropriate initial value (the empty list in this example) > for the accumulator : > > Python 2.7.1 (r271:86832, Jul 31 2011, 19:30:53) > [GCC 4.2.1 (Based on Apple Inc. build 5658) (LLVM build 2335.15.00)] on darwin > Type "help", "copyright", "credits" or "license" for more information. >>>> sum([[1,2],[3,4]], []) > [1, 2, 3, 4] I know that you just meant this as an example, but it's worth mentioning in this context that it's not exactly efficient to "sum up" lists this way because there is a lot of copying involved. Each adding of two lists creates a third one and copies all elements into it. So it eats a lot of time and space. Stefan