Path: csiph.com!usenet.pasdenom.info!aioe.org!news.stack.nl!newsfeed.xs4all.nl!newsfeed3.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; 'else:': 0.03; 'lines,': 0.07; 'subject:file': 0.07; 'subject:two': 0.07; 'data:': 0.09; 'iterate': 0.09; 'logic': 0.09; 'pointers': 0.09; 'received:80.91': 0.09; 'received:80.91.229': 0.09; 'received:gmane.org': 0.09; 'received:list': 0.09; 'python': 0.11; '"*"': 0.16; '(say': 0.16; '20)': 0.16; '3):': 0.16; 'file))': 0.16; 'itertools': 0.16; 'loop.': 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; 'true:': 0.16; 'alpha': 0.16; 'wrote:': 0.18; 'basically': 0.19; 'help.': 0.21; 'example': 0.22; 'import': 0.22; 'python?': 0.22; 'print': 0.22; 'header:User-Agent:1': 0.23; 'delta': 0.24; 'simpler': 0.24; 'certain': 0.27; 'header:X-Complaints-To:1': 0.27; 'lines': 0.31; 'prints': 0.31; 'file': 0.32; 'this.': 0.32; 'another': 0.32; 'actual': 0.34; 'subject:with': 0.35; 'requirement': 0.35; 'next': 0.36; 'hi,': 0.36; 'so,': 0.37; 'two': 0.37; 'starting': 0.37; 'to:addr:python-list': 0.38; 'to:addr:python.org': 0.39; 'received:org': 0.40; 'how': 0.40; 'break': 0.61; 'till': 0.61; 'more': 0.64; 'relatively': 0.65; 'detail.': 0.68; 'containing': 0.69; 'subject:over': 0.84 X-Injected-Via-Gmane: http://gmane.org/ To: python-list@python.org From: Peter Otten <__peter__@web.de> Subject: Re: iterating over a file with two pointers Date: Wed, 18 Sep 2013 13:44:10 +0200 Organization: None References: <3018b3d4-f914-4c89-9f26-cd4b2af32e73@googlegroups.com> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7Bit X-Gmane-NNTP-Posting-Host: p5084b6fc.dip0.t-ipconnect.de User-Agent: KNode/4.7.3 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: 62 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1379504643 news.xs4all.nl 15950 [2001:888:2000:d::a6]:56755 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:54374 nikhil Pandey wrote: > hi, > I want to iterate over the lines of a file and when i find certain lines, > i need another loop starting from the next of that "CERTAIN" line till a > few (say 20) lines later. so, basically i need two pointers to lines (one > for outer loop(for each line in file)) and one for inner loop. How can i > do that in python? please help. I am stuck up on this. Here's an example that prints the three lines following a line containing a '*': Example data: $ cat tmp.txt alpha *beta *gamma delta epsilon zeta *eta The python script: $ cat tmp.py from itertools import islice, tee with open("tmp.txt") as f: while True: for outer in f: print outer, if "*" in outer: f, g = tee(f) for inner in islice(g, 3): print " ", inner, break else: break The script's output: $ python tmp.py alpha *beta *gamma delta epsilon *gamma delta epsilon zeta delta epsilon zeta *eta $ As you can see the general logic is relatively complex; it is likely that we can come up with a simpler solution if you describe your actual requirement in more detail.