Path: csiph.com!usenet.pasdenom.info!gegeweb.org!de-l.enfer-du-nord.net!feeder1.enfer-du-nord.net!feeds.phibee-telecom.net!newsfeed.xs4all.nl!newsfeed4.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; 'example:': 0.03; 'argument': 0.05; 'beginner': 0.05; 'string': 0.09; 'way:': 0.09; 'subject:question': 0.10; 'python': 0.11; 'language.': 0.14; "'a',": 0.16; "'c',": 0.16; "'d',": 0.16; 'from:addr:mrabarnett.plus.com': 0.16; 'from:addr:python': 0.16; 'from:name:mrab': 0.16; 'message-id:@mrabarnett.plus.com': 0.16; 'missing?': 0.16; 'subject:beginner': 0.16; 'surprises': 0.16; 'wrote:': 0.18; 'trying': 0.19; 'everyone,': 0.19; '>>>': 0.22; 'header:User-Agent:1': 0.23; 'headers': 0.24; 'removed.': 0.24; 'simpler': 0.24; 'string,': 0.24; 'subject:problem': 0.24; 'header': 0.24; 'file.': 0.24; 'script': 0.25; 'code:': 0.26; 'header:In-Reply-To:1': 0.27; 'characters': 0.30; 'sets': 0.30; 'strip': 0.31; 'such.': 0.31; 'text': 0.33; 'something': 0.35; 'should': 0.36; 'to:addr:python-list': 0.38; 'to:addr:python.org': 0.39; 'numbers': 0.61; 'such': 0.63; 'header:Reply-To:1': 0.67; 'reply-to:no real name:2**0': 0.71; 'happening?': 0.84; 'reply- to:addr:python.org': 0.84 X-CM-Score: 0.00 X-CNFS-Analysis: v=2.1 cv=KrN0hwmN c=1 sm=1 tr=0 a=0nF1XD0wxitMEM03M9B4ZQ==:117 a=0nF1XD0wxitMEM03M9B4ZQ==:17 a=0Bzu9jTXAAAA:8 a=oyR3mlnJdzkA:10 a=JCJ9wb98zREA:10 a=ihvODaAuJD4A:10 a=OUOv7kDek9cA:10 a=8nJEP1OIZ-IA:10 a=EBOSESyhAAAA:8 a=8AHkEIZyAAAA:8 a=_5o13rfjvDMA:10 a=TUod_fgIGRTk15JOd7kA:9 a=wPNLvfGTeEIA:10 X-AUTH: mrabarnett:2500 Date: Tue, 04 Jun 2013 16:48:55 +0100 From: MRAB User-Agent: Mozilla/5.0 (Windows NT 5.1; rv:17.0) Gecko/20130509 Thunderbird/17.0.6 MIME-Version: 1.0 To: python-list@python.org Subject: Re: lstrip problem - beginner question References: <1829efca-935d-4049-ba61-7138015a2806@googlegroups.com> In-Reply-To: <1829efca-935d-4049-ba61-7138015a2806@googlegroups.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-BeenThere: python-list@python.org X-Mailman-Version: 2.1.15 Precedence: list Reply-To: python-list@python.org 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: 49 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1370360924 news.xs4all.nl 15992 [2001:888:2000:d::a6]:37133 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:46924 On 04/06/2013 16:21, mstagliamonte wrote: > Hi everyone, > > I am a beginner in python and trying to find my way through... :) > > I am writing a script to get numbers from the headers of a text file. > > If the header is something like: > h01 = ('>scaffold_1') > I just use: > h01.lstrip('>scaffold_') > and this returns me '1' > > But, if the header is: > h02: ('>contig-100_0') > if I use: > h02.lstrip('>contig-100_') > this returns me with: '' > ...basically nothing. What surprises me is that if I do in this other way: > h02b = h02.lstrip('>contig-100') > I get h02b = ('_1') > and subsequently: > h02b.lstrip('_') > returns me with: '1' which is what I wanted! > > Why is this happening? What am I missing? > The methods 'lstrip', 'rstrip' and 'strip' don't strip a string, they strip characters. You should think of the argument as a set of characters to be removed. This code: h01.lstrip('>scaffold_') will return the result of stripping the characters '>', '_', 'a', 'c', 'd', 'f', 'l', 'o' and 's' from the left-hand end of h01. A simpler example: >>> 'xyyxyabc'.lstrip('xy') 'abc' It strips the characters 'x' and 'y' from the string, not the string 'xy' as such. They are that way because they have been in Python for a long time, long before sets and such like were added to the language.