Path: csiph.com!usenet.pasdenom.info!weretis.net!feeder4.news.weretis.net!rt.uk.eu.org!newsfeed.xs4all.nl!newsfeed3.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 0.002 X-Spam-Evidence: '*H*': 1.00; '*S*': 0.00; 'python.': 0.02; 'memory.': 0.07; 'executed': 0.09; 'extracted': 0.09; 'raises': 0.09; 'received:80.91': 0.09; 'received:80.91.229': 0.09; 'received:gmane.org': 0.09; 'received:list': 0.09; 'def': 0.12; 'heap': 0.16; 'heapq': 0.16; 'iterating': 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; 'sorted()': 0.16; 'elements': 0.16; 'pushed': 0.16; 'wrote:': 0.18; 'bit': 0.19; '>>>': 0.22; 'import': 0.22; 'header :User-Agent:1': 0.23; 'adds': 0.24; 'header:X-Complaints-To:1': 0.27; 'function': 0.29; 'raise': 0.29; 'dec': 0.30; "skip:' 10": 0.31; '+0100,': 0.31; 'lessons': 0.31; 'file': 0.32; 'thanks!': 0.32; "i'd": 0.34; 'could': 0.34; 'except': 0.35; 'but': 0.35; 'yield': 0.36; 'doing': 0.36; 'thanks': 0.36; 'hi,': 0.36; 'application': 0.37; 'so,': 0.37; 'too': 0.37; 'list': 0.37; 'list.': 0.37; 'to:addr:python-list': 0.38; 'to:addr:python.org': 0.39; 'received:org': 0.40; 'how': 0.40; 'save': 0.62; 'complete': 0.62; 'real': 0.63; 'subject:more': 0.64; 'more': 0.64; 'here': 0.66; 'subject:there': 0.68; 'below.': 0.71; 'end.': 0.84; 'otten': 0.84; '2013': 0.98 X-Injected-Via-Gmane: http://gmane.org/ To: python-list@python.org From: Peter Otten <__peter__@web.de> Subject: Re: extracting a heapq in a for loop - there must be more elegant solution Date: Wed, 04 Dec 2013 10:50:52 +0100 Organization: None References: Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7Bit X-Gmane-NNTP-Posting-Host: p5084b2f9.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: 64 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1386150658 news.xs4all.nl 2830 [2001:888:2000:d::a6]:42089 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:61002 Helmut Jarausch wrote: > On Tue, 03 Dec 2013 13:38:58 +0100, Peter Otten wrote: > >> Helmut Jarausch wrote: >> >>> Hi, >>> >>> I'd like to extracted elements from a heapq in a for loop. >>> I feel my solution below is much too complicated. >>> How to do it more elegantly? >>> I know I could use a while loop but I don't like it. >>> >>> Many thanks for some lessons in Python. >>> >>> Here is my clumsy solution >>> >>> from heapq import heappush, heappop >>> # heappop raises IndexError if heap is empty >>> >>> H=[] >>> for N in 'H','C','W','I' : >>> heappush(H,N) >> >> H = ["H", "C", "W", "I"] >> heapq.heapify(H) >> >> But see below. >> >>> # how to avoid / simplify the following function >>> >>> def in_sequence(H) : >>> try : >>> while True : >>> N= heappop(H) >>> yield N >>> except IndexError : >>> raise StopIteration >>> >>> # and here the application: >>> >>> for N in in_sequence(H) : >>> print(N) >> >> If you are iterating over the complete heap I see no advantage over a >> sorted list. So >> >> for N in sorted(H): >> print(N) >> >> If H is huge use H.sort() instead of sorted() to save memory. >> If you need only a few items use heapq.nsmallest(). > > > Many thanks! > In my real application the data which is pushed onto the heap will be > extracted from a small file which is executed several thousands times. So, > I thought, I could keep the CPU a bit busy while the OS is doing file I/O. > Of course, I could have appended all these strings to a list which is > sorted at the end. In that case have a look at bisect.insort() which adds an item to a list while keeping it sorted.