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!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 0.004 X-Spam-Evidence: '*H*': 0.99; '*S*': 0.00; 'anyway.': 0.05; 'subject:Python': 0.06; 'skip:` 10': 0.07; 'apis': 0.09; 'from:addr:ethan': 0.09; 'from:addr:stoneleaf.us': 0.09; 'from:name:ethan furman': 0.09; 'message-id:@stoneleaf.us': 0.09; 'received:184.172': 0.09; 'received:gator410.hostgator.com': 0.09; 'subject:()': 0.09; '~ethan~': 0.09; 'api': 0.11; 'python': 0.11; 'thread': 0.14; 'api,': 0.16; 'failure.': 0.16; 'previously,': 0.16; 'all.': 0.16; 'wrote:': 0.18; 'stefan': 0.19; '>>>': 0.22; 'header:User-Agent:1': 0.23; 'looks': 0.24; 'question': 0.24; 'header:In-Reply-To:1': 0.27; 'am,': 0.29; 'gives': 0.31; 'commonly': 0.31; 'etc.).': 0.31; 'common': 0.35; 'problem.': 0.35; 'something': 0.35; 'operations': 0.35; 'but': 0.35; 'method': 0.36; 'charset:us-ascii': 0.36; 'so,': 0.37; 'two': 0.37; 'being': 0.38; 'needed': 0.38; 'to:addr:python-list': 0.38; 'skip:. 10': 0.39; 'to:addr:python.org': 0.39; 'how': 0.40; 'received:173': 0.61; 'simply': 0.61; 'more': 0.64; 'different': 0.65; 'useful.': 0.68; 'subject: & ': 0.68; 'increase': 0.74; 'special': 0.74; 'hey,': 0.75; 'ethan': 0.84; 'everything.': 0.84; 'furman': 0.84; 'received:64.5': 0.84 Date: Wed, 24 Jul 2013 11:31:58 -0700 From: Ethan Furman User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:16.0) Gecko/20121010 Thunderbird/16.0.1 MIME-Version: 1.0 To: python-list@python.org Subject: Re: Python 3: dict & dict.keys() References: <51EF2AD8.3080105@stoneleaf.us> In-Reply-To: Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - gator410.hostgator.com X-AntiAbuse: Original Domain - python.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - stoneleaf.us X-BWhitelist: no X-Source: X-Source-Args: X-Source-Dir: X-Source-Sender: ([173.12.184.233]) [173.12.184.233]:44909 X-Source-Auth: ethan+stoneleaf.us X-Email-Count: 7 X-Source-Cap: dG9idWs7dG9idWs7Z2F0b3I0MTAuaG9zdGdhdG9yLmNvbQ== 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: 29 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1374692206 news.xs4all.nl 15873 [2001:888:2000:d::a6]:54804 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:51161 On 07/24/2013 10:23 AM, Stefan Behnel wrote: > Peter Otten, 24.07.2013 08:23: >> Ethan Furman wrote: >>> >>> So, my question boils down to: in Python 3 how is dict.keys() different >>> from dict? What are the use cases? >> >> To me it looks like views are a solution waiting for a problem. > > They reduce the API overhead. Previously, you needed values() and > itervalues(), with values() being not more than a special case of what > itervalues() provides anyway. Now it's just one method that gives you > everything. It simply has corrected the tradeoff from two special purpose > APIs to one general purpose API, that's all. I started this thread for two reasons: 1) Increase awareness that using `list(dict)` is a cross-version replacement for `dict.keys()` 2) Hopefully learn something about when a view is useful. So far #2 is pretty much a failure. Only one use-case so far (and it feels pretty rare). But hey, I have learned that while some set operations are allowed (&, ^, |, .isdisjoint()), others are not (.remove(), .discard(), .union(), etc.). The old .keys(), .values(), and .items() (and their .iter...() variations) did something commonly useful. Of what common use are these views? -- ~Ethan~