Path: csiph.com!v102.xanadu-bbs.net!xanadu-bbs.net!news.albasani.net!rt.uk.eu.org!newsfeed.xs4all.nl!newsfeed4a.news.xs4all.nl!xs4all!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; 'example:': 0.03; '"this': 0.03; 'resulting': 0.04; 'yet.': 0.04; 'context': 0.07; 'matches': 0.07; '"("': 0.09; 'literal': 0.09; 'received:80.91': 0.09; 'received:80.91.229': 0.09; 'received:gmane.org': 0.09; 'received:list': 0.09; 'subject:How': 0.10; '"..."': 0.16; "'a',": 0.16; "'b',": 0.16; 'components.': 0.16; 'delimiters': 0.16; 'example?': 0.16; 'received:80.91.229.3': 0.16; 'received:dip0.t-ipconnect.de': 0.16; 'received:plane.gmane.org': 0.16; 'received:t-ipconnect.de': 0.16; 'set,': 0.16; 'simplified': 0.16; 'wrote:': 0.18; '>>>': 0.22; 'example': 0.22; 'import': 0.22; 'header:User-Agent:1': 0.23; 'url:moin': 0.24; 'helpful': 0.24; 'looks': 0.24; 'header:X-Complaints-To:1': 0.27; 'url:wiki': 0.31; 'quite': 0.32; 'url:python': 0.33; 'not.': 0.33; 'subject:the': 0.34; 'could': 0.34; 'but': 0.35; 'hi,': 0.36; 'url:org': 0.36; 'two': 0.37; 'list.': 0.37; 'sometimes': 0.38; 'to:addr:python-list': 0.38; 'anything': 0.39; 'does': 0.39; 'quote': 0.39; 'to:addr:python.org': 0.39; 'received:org': 0.40; 'skip:u 10': 0.60; 'break': 0.61; 'simple': 0.61; 'complete': 0.62; 'more': 0.64; 'link:': 0.72; 'therefore': 0.72; 'special': 0.74; 'group)': 0.84; 'broadcasting': 0.91 X-Injected-Via-Gmane: http://gmane.org/ To: python-list@python.org From: Peter Otten <__peter__@web.de> Subject: Re: How to decipher :re.split(r"(\(\([^)]+\)\))" in the example Date: Thu, 10 Jul 2014 18:49:28 +0200 Organization: None References: <981c1f5f-2c19-4efc-8397-796bde07f39b@googlegroups.com> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7Bit X-Gmane-NNTP-Posting-Host: p57bda429.dip0.t-ipconnect.de User-Agent: KNode/4.11.5 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: 60 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1405010988 news.xs4all.nl 2951 [2001:888:2000:d::a6]:56078 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:74316 fl wrote: > Hi, > > This example is from the link: > > https://wiki.python.org/moin/RegularExpression > > > I have thought about it quite a while without a clue yet. I notice that it > uses double quote ", in contrast to ' which I see more often until now. > It looks very complicated to me. Could you simplified it to a simple > example? Just break it into its components. "(...)" in the context of re.split() keeps the delimiters while just "..." does not. Example: >>> re.split("a+", "abbaaababa") ['', 'bb', 'b', 'b', ''] >>> re.split("(a+)", "abbaaababa") ['', 'a', 'bb', 'aaa', 'b', 'a', 'b', 'a', ''] r"\(" matches the openening parenthesis. The "(" has to be escaped because it otherwise has a special meaning (begin group) in a regex. "[abc]" matches a, b, or c. A leading ^ inverts the set, so "[^abc]" matches anything but a, b, or c. Therefore "[^)]" matches anything but the closing parenthesis. The complete regex then is: match two opening parens, then one or more chars that are not closing parens, then two closing parens, and make the complete group part of the resulting list. PS: Note that sometimes the re.DEBUG flag may be helpful in understanding noisy regexes: subpattern 1 literal 40 literal 40 max_repeat 1 4294967295 not_literal 41 literal 41 literal 41 <_sre.SRE_Pattern object at 0x7f5740455c90> > import re > split_up = re.split(r"(\(\([^)]+\)\))", > "This is a ((test)) of the ((emergency broadcasting > station.))") > > > ...which produces: > > > ["This is a ", "((test))", " of the ", "((emergency broadcasting > [station.))" ]