Path: csiph.com!x330-a1.tempe.blueboxinc.net!usenet.pasdenom.info!aioe.org!feeder.news-service.com!newsfeed.xs4all.nl!newsfeed5.news.xs4all.nl!xs4all!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; 'does.': 0.07; 'python': 0.08; 'mutable': 0.09; 'received:80.91': 0.09; 'received:80.91.229': 0.09; 'received:80.91.229.12': 0.09; 'received:gmane.org': 0.09; 'received:list': 0.09; 'received:lo.gmane.org': 0.09; 'wed,': 0.13; '"="': 0.16; '"writable"': 0.16; '3],': 0.16; 'bieber': 0.16; 'blah': 0.16; 'declaimed': 0.16; 'email addr:ix.netcom.com': 0.16; 'email name:wlfraed': 0.16; 'from:addr:ix.netcom.com': 0.16; 'from:addr:wlfraed': 0.16; 'from:name:dennis lee bieber': 0.16; 'it...': 0.16; 'iterator': 0.16; 'received:66.245': 0.16; 'received:dsl.mindspring.com': 0.16; 'received:mindspring.com': 0.16; 'received:wlfraed': 0.16; 'to"': 0.16; 'translates': 0.16; 'url:netcom': 0.16; 'url:wlfraed': 0.16; 'wulfraed': 0.16; 'object,': 0.16; '>>>': 0.16; 'loop,': 0.23; 'refers': 0.23; 'url:home': 0.25; 'lee': 0.28; '24,': 0.29; 'object': 0.30; 'subject:?': 0.31; 'connected': 0.32; 'header:X-Complaints-To:1': 0.34; 'to:addr:python-list': 0.34; 'assignment': 0.35; 'charset :us-ascii': 0.36; 'limitation': 0.37; 'but': 0.37; 'received:org': 0.38; 'something': 0.38; 'subject:: ': 0.38; 'header:Mime- Version:1': 0.39; 'to:addr:python.org': 0.39; 'your': 0.61; 'believe': 0.66; '"for': 0.67; 'jun': 0.67; 'dennis': 0.77; "'e'": 0.84; '[[1,': 0.84; 'sequence:': 0.84 X-Injected-Via-Gmane: http://gmane.org/ To: python-list@python.org From: Dennis Lee Bieber Subject: Re: writable iterators? Date: Wed, 22 Jun 2011 21:50:22 -0700 Organization: > Bestiaria Support Staff < References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Gmane-NNTP-Posting-Host: user-11faedd.dsl.mindspring.com X-Newsreader: Forte Agent 3.3/32.846 X-No-Archive: YES 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: 42 NNTP-Posting-Host: 82.94.164.166 X-Trace: 1308804643 news.xs4all.nl 14137 [::ffff:82.94.164.166]:39166 X-Complaints-To: abuse@xs4all.nl Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:8262 On Wed, 22 Jun 2011 15:28:23 -0400, Neal Becker declaimed the following in gmane.comp.python.general: > for e in sequence: > do something that reads e > e = blah # will do nothing > > I believe this is not a limitation on the for loop, but a limitation on the > python iterator concept. Is this correct? Neither... It is a misunderstanding of what "=" assignment DOES. e = blah translates into "disconnect the NAME 'e' from whatever object it currently refers to; connect the NAME 'e' to the same object that the name 'blah" is connected to" "for e in sequence" connects the name "e" to then next object in the iterable. As long as your "writable" is a MUTABLE object, you CAN mutate it... >>> lol = [ [1, 2, 3], ... [4, 5, 6], ... [7, 8, 9] ] >>> for e in lol: ... e[1] = sum(e) ... >>> lol [[1, 6, 3], [4, 15, 6], [7, 24, 9]] >>> >>> for e in lol: ... e.reverse() ... >>> lol [[3, 6, 1], [6, 15, 4], [9, 24, 7]] >>> -- Wulfraed Dennis Lee Bieber AF6VN wlfraed@ix.netcom.com HTTP://wlfraed.home.netcom.com/