Path: csiph.com!usenet.pasdenom.info!weretis.net!feeder4.news.weretis.net!feeds.phibee-telecom.net!newsfeed.xs4all.nl!newsfeed4a.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; 'nasty': 0.07; 'returns,': 0.09; 'cc:addr:python-list': 0.11; 'python': 0.11; 'jan': 0.12; 'changes': 0.15; "('c',": 0.16; '(which,': 0.16; '1),': 0.16; '3)]': 0.16; '8:40': 0.16; "[('a',": 0.16; 'charles': 0.16; 'dict': 0.16; 'from:addr:rosuav': 0.16; 'from:name:chris angelico': 0.16; 'read-only.': 0.16; 'roy': 0.16; 'shallow': 0.16; 'values?': 0.16; 'wording': 0.16; 'wrote:': 0.18; 'subject:request': 0.19; '>>>': 0.22; 'cc:addr:python.org': 0.22; 'documented': 0.24; 'mon,': 0.24; 'cc:2**0': 0.24; 'pass': 0.26; 'header:In-Reply-To:1': 0.27; 'function': 0.29; 'am,': 0.29; "doesn't": 0.30; 'returned': 0.30; 'message-id:@mail.gmail.com': 0.30; 'are.': 0.31; 'could': 0.34; 'no,': 0.35; 'received:google.com': 0.35; 'really': 0.36; 'method': 0.36; 'list': 0.37; 'expected': 0.38; 'lists.': 0.38; 'itself': 0.39; 'read': 0.60; 'affect': 0.61; "you're": 0.61; 'talking': 0.65; '20,': 0.68; 'smith': 0.68; 'subject': 0.69; 'article': 0.77; 'p.s.:': 0.84; 'to:none': 0.92 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=2S3VASIIpBWVbxLJQLstIxD9RwrIZXTY6Tbc0t0sfXA=; b=N9V+fqcsHsyAt0jWLpPwpgubLhUj+prdbX48rU60IZueGi/5nBd/BV2t0UIJf7f2M8 tvuM+kScJNwl6WStvJSHVVAXbahEt7GXi0xlayxy0gWeqzSGSlOg2/AcQelUlFFdtDNk ytZun/N6XX+3kr4iqbjdVAm/FpNmNqFNXlelpCSwgV+Sucv7wgAe5wdbGGSxotkhJnx7 SKNOXSIdk9Lh+zo5l0sJKRlv8BymO0f43iRa7Hk1w9nPwRGZyuhjgvM9xFxYJJ9PL+Tk SY9d7F41YlT3Tgtv6ZBpnsoaRJOKnj03alzT8U0lItcbTRfzsoOmXFPBSKb4fFACDCik CDxQ== MIME-Version: 1.0 X-Received: by 10.68.201.71 with SMTP id jy7mr15016117pbc.47.1390168602494; Sun, 19 Jan 2014 13:56:42 -0800 (PST) In-Reply-To: References: Date: Mon, 20 Jan 2014 08:56:42 +1100 Subject: Re: Documentation of dict views change request From: Chris Angelico Cc: "python-list@python.org" 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: 35 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1390168611 news.xs4all.nl 2855 [2001:888:2000:d::a6]:40419 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:64329 On Mon, Jan 20, 2014 at 8:40 AM, Roy Smith wrote: > In article , > Charles Hixson wrote: > >> Could it please be clearly documented that keys(), values(), and items() >> are not writeable. > > We'll, technically, they are. > > Of course, this only changes the list that keys() returns, it doesn't > affect the dictionary itself (which, I assume, is what you were really > talking about). In Python 3, they return views, not lists. So they really are read-only. On Mon, Jan 20, 2014 at 8:26 AM, Charles Hixson wrote: > P.S.: Is it reasonable to return the items() of a dict in order to pass a > read only copy of the values? No, because it isn't a copy. At least, not in Python 3; if you're using Python 2, then the wording of your subject line is inaccurate, see above. >>> d = {"a":1,"b":2,"c":3} >>> i = d.items() >>> del d["b"] >>> list(i) [('a', 1), ('c', 3)] If you returned i from a function and expected it to be a copy, you'd be in for a nasty shock. Try the .copy() method for a shallow copy, or look up deepcopy if you need a recursive copy. ChrisA