Path: csiph.com!usenet.pasdenom.info!weretis.net!feeder4.news.weretis.net!feeds.phibee-telecom.net!newsfeed.xs4all.nl!newsfeed2.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 0.003 X-Spam-Evidence: '*H*': 0.99; '*S*': 0.00; 'element': 0.07; '*is*': 0.09; 'logic': 0.09; 'slow.': 0.09; 'cc:addr:python-list': 0.11; '"in"': 0.16; 'element.': 0.16; 'exist.': 0.16; 'from:addr:rosuav': 0.16; 'from:name:chris angelico': 0.16; 'iterable': 0.16; 'iterating': 0.16; 'iteration.': 0.16; 'itertools': 0.16; 'returned,': 0.16; 'subject:slow': 0.16; 'tuples,': 0.16; 'wrote:': 0.18; 'wed,': 0.18; 'import': 0.22; 'cc:addr:python.org': 0.22; 'cc:2**0': 0.24; 'pass': 0.26; 'gets': 0.27; 'header:In-Reply-To:1': 0.27; 'thus': 0.29; 'dec': 0.30; 'message-id:@mail.gmail.com': 0.30; 'concern': 0.31; 'another': 0.32; 'problem': 0.35; 'test': 0.35; 'but': 0.35; 'received:google.com': 0.35; 'really': 0.36; 'next': 0.36; 'example,': 0.37; 'represent': 0.38; 'checks': 0.38; 'pm,': 0.38; 'sure': 0.39; 'skip:p 20': 0.39; 'space': 0.40; 'skip:x 10': 0.40; 'entire': 0.61; 'first': 0.61; 'to:none': 0.92; 'hundred': 0.95 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:cc :content-type; bh=IUPt7ch5PETXbh76IU/0/ATYhbkCimWJt39fiYhyYs0=; b=glHokEmH58GZ9o3UdYOen+kEgLsYBJia0bXihAo/WjDQMxlubOisK9vRrWv1RDQzsm IxDFtwakoVRHHXrWXBCJW+5C/J7j4JoWzaBZ1iLFFiRWO8xI1ANa0f86mVhqWCgxd9qI tNTTLhtYfrgDW3XiUlq5A+4EVNQLgVXKVb6n3tO3zewvgrLmEukqSh+cPzcOrYgIybQS 81mx9M96UYLOruWE3+HWpPQHMQONJfSTXrthB2ZEgEK2KfE97z7e2NUwOSGYP+ps0p08 cgplnHOP/UJzG5IxdX10NTITSKNwd5NZLm9154Sw4ZKM7884yWfmTdQTG7xE569NYG/6 RvyQ== MIME-Version: 1.0 X-Received: by 10.42.130.194 with SMTP id w2mr5399330ics.12.1418193005154; Tue, 09 Dec 2014 22:30:05 -0800 (PST) In-Reply-To: <20141210052025.GA84184@FuzzyHorror> References: <20141210052025.GA84184@FuzzyHorror> Date: Wed, 10 Dec 2014 17:30:05 +1100 Subject: Re: Nested loops is strangely slow, totally at a loss. From: Chris Angelico Cc: Python Content-Type: text/plain; charset=UTF-8 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: 27 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1418193013 news.xs4all.nl 2922 [2001:888:2000:d::a6]:42047 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:82263 On Wed, Dec 10, 2014 at 4:20 PM, Shiyao Ma wrote: > from itertools import product > space_len = 580 > space = product(xrange(space_len), xrange(space_len), xrange(space_len)) > > sparse_cloud = product(xrange(1000), xrange(1000), xrange(1000)) > for i, j, k in sparse_cloud: > ts = timeit.default_timer() > if (i, j, k) in space: pass > te = timeit.default_timer() On Wed, Dec 10, 2014 at 4:23 PM, Shiyao Ma wrote: > One thing to note, the logic of using "in" is not of concern here. > This is a *contrived* example, the problem is the slowness of the first > iteration. Are you sure it isn't? Your 'space' is an iterable cubic cross-product. Your first loop checks (0,0,0) which is the first element returned, and is thus fast... but it also *consumes* that first element. The next time you test it, the entire space gets consumed, looking for another (0,0,0), which won't exist. That means iterating over 580**3 == 195112000 (two hundred million) tuples, and that *is* going to be slow. Is product() really the right way to represent your space? ChrisA