Path: csiph.com!usenet.pasdenom.info!gegeweb.org!de-l.enfer-du-nord.net!feeder2.enfer-du-nord.net!newsfeed.eweka.nl!eweka.nl!feeder3.eweka.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 0.007 X-Spam-Evidence: '*H*': 0.99; '*S*': 0.00; 'explicitly': 0.05; 'subject:Python': 0.06; 'iterate': 0.09; 'received:80.91': 0.09; 'received:80.91.229': 0.09; 'received:gmane.org': 0.09; 'received:list': 0.09; 'skip:/ 10': 0.09; 'subject:()': 0.09; 'wrapped': 0.09; 'python': 0.11; '24,': 0.16; 'benjamin': 0.16; 'iterated': 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; 'set,': 0.16; 'wrote:': 0.18; '>>>': 0.22; 'example': 0.22; 'header:User-Agent:1': 0.23; '2.x': 0.24; 'either.': 0.24; 'looks': 0.24; '(or': 0.24; 'question': 0.24; 'header:X-Complaints-To:1': 0.27; 'am,': 0.29; 'code': 0.31; 'keys': 0.31; 'lists': 0.32; 'skip:m 30': 0.32; 'guess': 0.33; 'actual': 0.34; 'could': 0.34; 'problem.': 0.35; 'but': 0.35; 'picking': 0.36; "didn't": 0.36; 'so,': 0.37; 'list': 0.37; 'to:addr:python-list': 0.38; 'rather': 0.38; 'to:addr:python.org': 0.39; 'either': 0.39; 'received:org': 0.40; 'users': 0.40; 'how': 0.40; 'even': 0.60; 'most': 0.60; 'identify': 0.61; 'different': 0.65; 'temporary': 0.65; 'subject: & ': 0.68; 'jul': 0.74; '7:25': 0.84; 'ethan': 0.84; 'furman': 0.84; 'idiom': 0.84; 'lying': 0.84; 'oscar': 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: Python 3: dict & dict.keys() Date: Wed, 24 Jul 2013 15:25:14 +0200 Organization: None References: <51EF2AD8.3080105@stoneleaf.us> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7Bit X-Gmane-NNTP-Posting-Host: p5084a7c8.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: 39 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1374672304 news.xs4all.nl 16009 [2001:888:2000:d::a6]:41778 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:51129 Oscar Benjamin wrote: > On Jul 24, 2013 7:25 AM, "Peter Otten" <__peter__@web.de> wrote: >> >> Ethan Furman wrote: >> >> > So, my question boils down to: in Python 3 how is dict.keys() >> > different >> > from dict? What are the use cases? >> >> I just grepped through /usr/lib/python3, and could not identify a single >> line where some_object.keys() wasn't either wrapped in a list (or set, >> sorted, max) call, or iterated over. >> >> To me it looks like views are a solution waiting for a problem. > > What do you mean? Why would you want to create a temporary list just to > iterate over it explicitly or implicitly (set, sorted, max,...)? I mean I don't understand the necessity of views when all actual usecases need iterators. The 2.x iterkeys()/iteritems()/itervalues() methods didn't create lists either. Do you have 2.x code lying around where you get a significant advantage by picking some_dict.viewkeys() over some_dict.iterkeys()? I could construct one >>> d = dict(a=1, b=2, c=3) >>> e = dict(b=4, c=5, d=6) >>> d.viewkeys() & e.viewkeys() set(['c', 'b']) but have not seen it in the wild. My guess is that most non-hardcore users don't even know about viewkeys(). By the way, my favourite idiom to iterate over the keys in both Python 2 and 3 is -- for example -- max(some_dict) rather than max(some_dict.whateverkeys()).