Path: csiph.com!usenet.pasdenom.info!news.albasani.net!newsfeed.freenet.ag!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 0.005 X-Spam-Evidence: '*H*': 0.99; '*S*': 0.00; 'from:addr:yahoo.co.uk': 0.04; 'pypi': 0.07; 'lawrence': 0.09; 'received:80.91': 0.09; 'received:80.91.229': 0.09; 'received:gmane.org': 0.09; 'received:list': 0.09; 'slow.': 0.09; 'subject:Why': 0.09; 'suggestions:': 0.09; 'bug': 0.12; 'assume': 0.14; '(use': 0.16; 'received:80.91.229.3': 0.16; 'received:plane.gmane.org': 0.16; 'roy': 0.16; 'subject:slow': 0.16; 'tempted': 0.16; 'version?': 0.16; 'wrote:': 0.18; 'module': 0.19; 'split': 0.19; 'seems': 0.21; '>>>': 0.22; 'creating': 0.23; 'header:User-Agent:1': 0.23; '2.x': 0.24; 'skip': 0.24; '---': 0.24; 'least': 0.26; 'header:X -Complaints-To:1': 0.27; 'header:In-Reply-To:1': 0.27; 'tried': 0.27; 'url:bugs': 0.29; 'matching': 0.30; "i'm": 0.30; '(which': 0.31; 'ball': 0.31; 'open': 0.33; 'url:python': 0.33; 'beginning': 0.33; 'could': 0.34; 'but': 0.35; 'next': 0.36; "didn't": 0.36; 'subject:?': 0.36; 'url:org': 0.36; 'easily': 0.37; 'performance': 0.37; 'to:addr:python-list': 0.38; 'pm,': 0.38; 'rather': 0.38; 'that,': 0.38; 'does': 0.39; 'to:addr:python.org': 0.39; 'received:org': 0.40; 'skip:u 10': 0.60; 'black': 0.61; 'gone': 0.61; 'new': 0.61; 'first': 0.61; 'making': 0.63; 'smith': 0.68; 'watching': 0.68; 'obvious': 0.74; 'yourself': 0.78; 'difference.': 0.84; 'email addr:panix.com': 0.84; 'white,': 0.84; 'received:89': 0.85; '2013,': 0.91 X-Injected-Via-Gmane: http://gmane.org/ To: python-list@python.org From: Mark Lawrence Subject: Re: Why is regex so slow? Date: Tue, 18 Jun 2013 18:34:01 +0100 References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Gmane-NNTP-Posting-Host: host-89-240-174-199.as13285.net User-Agent: Mozilla/5.0 (Windows NT 6.0; rv:17.0) Gecko/20130509 Thunderbird/17.0.6 In-Reply-To: X-Antivirus: avast! (VPS 130618-0, 18/06/2013), Outbound message X-Antivirus-Status: Clean X-BeenThere: python-list@python.org X-Mailman-Version: 2.1.15 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: 40 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1371576854 news.xs4all.nl 16004 [2001:888:2000:d::a6]:43092 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:48648 On 18/06/2013 18:08, Roy Smith wrote: > > On Jun 18, 2013, at 1:01 PM, Skip Montanaro wrote: > >>> I don't understand why the first way is so much slower. >> >> I have no obvious answers, but a couple suggestions: >> >> 1. Can you anchor the pattern at the beginning of the line? (use >> match() instead of search()) > > That's one of the things we tried. Didn't make any difference. > >> 2. Does it get faster it you eliminate the "(.*)" part of the pattern? > > Just tried that, it also didn't make any difference. > >> It seems that if you find a line matching the first part of the >> pattern, you could just as easily split the line yourself instead of >> creating a group. > > > At this point, I'm not so much interested in making this faster as understanding why it's so slow. I'm tempted to open this up as a performance bug against the regex module (which I assume will be rejected, at least for the 2.x series). > > --- > Roy Smith > roy@panix.com > Out of curiousity have the tried the new regex module from pypi rather than the stdlib version? A heck of a lot of work has gone into it see http://bugs.python.org/issue2636 -- "Steve is going for the pink ball - and for those of you who are watching in black and white, the pink is next to the green." Snooker commentator 'Whispering' Ted Lowe. Mark Lawrence