Path: csiph.com!x330-a1.tempe.blueboxinc.net!usenet.pasdenom.info!selfless.tophat.at!newsfeed.xs4all.nl!newsfeed6.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 0.008 X-Spam-Evidence: '*H*': 0.98; '*S*': 0.00; 'python': 0.07; '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; 'solution,': 0.09; 'wrote:': 0.14; 'contrary,': 0.16; 'received:dip.t-dialin.net': 0.16; 'received:t-dialin.net': 0.16; 'runs,': 0.16; 'subject:Converting': 0.16; 'subject:set': 0.16; 'transforming': 0.16; 'subject:list': 0.22; 'loop': 0.22; 'equivalent': 0.26; 'daniel': 0.29; 'list': 0.30; 'seem': 0.30; 'from:addr:web.de': 0.31; 'operation.': 0.31; 'to:addr:python- list': 0.32; 'another': 0.32; 'header:X-Complaints-To:1': 0.34; 'skip:" 10': 0.34; 'less': 0.38; 'but': 0.38; 'received:org': 0.38; 'set': 0.39; 'to:addr:python.org': 0.39; 'header:Mime- Version:1': 0.39; 'header:Received:5': 0.40; 'might': 0.40; 'best': 0.60; 'back': 0.61; 'conversion': 0.64; '100': 0.70; 'concerns': 0.80; '1.99': 0.84; 'marginally': 0.84; 'speed,': 0.84 X-Injected-Via-Gmane: http://gmane.org/ To: python-list@python.org From: Peter Otten <__peter__@web.de> Subject: Re: Converting a set into list Date: Mon, 16 May 2011 08:34:44 +0200 Organization: None References: <87iptdid68.fsf@benfinney.id.au> <871v00j2bh.fsf@benfinney.id.au> <34fc571c-f382-405d-94b1-0a673da5f46b@t16g2000vbi.googlegroups.com> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7Bit X-Gmane-NNTP-Posting-Host: p5084908d.dip.t-dialin.net 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: 40 NNTP-Posting-Host: 82.94.164.166 X-Trace: 1305527630 news.xs4all.nl 81474 [::ffff:82.94.164.166]:60771 X-Complaints-To: abuse@xs4all.nl Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:5493 Daniel Kluev wrote: >> Both solutions seem to be equivalent in that concerns the number of >> needed loop runs, but this two-step operation might require one less loop >> over list1. The set&set solution, in contrary, might require one loop >> while transforming to a set and another one for the & operation. > > python -m timeit -s "l1 = range(1, 10000); l2 = range(5000, 15000)" > "l3 = list(set(l1) & set(l2))" > 100 loops, best of 3: 2.19 msec per loop > > python -m timeit -s "l1 = range(1, 10000); l2 = range(5000, 15000)" > "s=set(l2); l3 = [i for i in l1 if i in s]" > 100 loops, best of 3: 2.45 msec per loop > > python -m timeit -s "l1 = range(1, 100000); l2 = range(50000, 150000)" > "l3 = list(set(l1) & set(l2))" > 10 loops, best of 3: 28 msec per loop > > python -m timeit -s "l1 = range(1, 100000); l2 = range(50000, 150000)" > "s=set(l2); l3 = [i for i in l1 if i in s]" > 10 loops, best of 3: 28.1 msec per loop > > So even with conversion back into list set&set is still marginally faster. If you are looking for speed, consider s = set(l1) s.intersection_update(l2) l3 = list(s) $ python -m timeit -s "l1 = range(1, 10000); l2 = range(5000, 15000)" "list(set(l1) & set(l2))" 100 loops, best of 3: 4 msec per loop $ python -m timeit -s "l1 = range(1, 10000); l2 = range(5000, 15000)" "s = set(l1); s.intersection_update(l2); list(s)" 100 loops, best of 3: 1.99 msec per loop