Path: csiph.com!usenet.pasdenom.info!weretis.net!feeder1.news.weretis.net!feeder.erje.net!eu.feeder.erje.net!newsfeed.xs4all.nl!newsfeed1a.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 0.000 X-Spam-Evidence: '*H*': 1.00; '*S*': 0.00; '(at': 0.04; 'resulting': 0.04; 'duplicate': 0.07; 'received:80.91': 0.09; 'received:80.91.229': 0.09; 'received:gmane.org': 0.09; 'received:list': 0.09; 'way:': 0.09; '2.7': 0.14; "'c',": 0.16; '-tkc': 0.16; 'evaluating': 0.16; 'least)': 0.16; 'lhs': 0.16; 'readable': 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; 'rhs': 0.16; 'subject:dictionaries': 0.16; "{'a':": 0.16; 'wrote:': 0.18; 'result.': 0.19; '>>>': 0.22; 'otherwise,': 0.22; 'preferred': 0.22; 'header:User-Agent:1': 0.23; 'propose': 0.24; 'replace': 0.24; 'skip': 0.24; 'earlier': 0.24; 'least': 0.26; 'header:X -Complaints-To:1': 0.27; 'correct': 0.29; 'tim': 0.29; 'sets': 0.30; '(on': 0.31; '3.x': 0.31; 'chase': 0.31; 'keys': 0.31; 'operations': 0.35; 'but': 0.35; "didn't": 0.36; 'possible': 0.36; 'two': 0.37; 'being': 0.38; 'to:addr:python-list': 0.38; 'to:addr:python.org': 0.39; 'received:org': 0.40; 'space': 0.40; 'save': 0.62; 'choose': 0.64; 'week,': 0.64 X-Injected-Via-Gmane: http://gmane.org/ To: python-list@python.org From: Peter Otten <__peter__@web.de> Subject: Re: intersection, union, difference, symmetric difference for dictionaries Date: Tue, 25 Feb 2014 22:54:43 +0100 Organization: None References: <20140225150351.063fd961@bigbox.christie.dr> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7Bit X-Gmane-NNTP-Posting-Host: p57bdad84.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: 57 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1393365296 news.xs4all.nl 2884 [2001:888:2000:d::a6]:48121 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:67064 Tim Chase wrote: > On 2014-02-25 14:40, Skip Montanaro wrote: >> What's the correct result of evaluating this expression? >> >> {'A': 1} | {'A': 2} >> >> I can see (at least) two possible "correct" answers. > > I would propose at least four: > > {'A': 1} # choose the LHS > {'A': 2} # choose the RHS > {'A': (1,2)} # a resulting pair of both > set(['A']) # you did set-ops, so you get a set > > If dicts were to support set ops, They do in 2.7 and 3.x. > the last one would be my preferred > result. > > I just had to perform set operations on a pair of dicts earlier this > week, shrugged, and did things the manual/explicit way: > > a_dict = dict(...) > b_dict = dict(...) > a_set = set(a_dict) > b_set = set(b_dict) > added_keys = b_set - a_set > removed_keys = a_set - b_set > same_keys = a_set & b_set > diff_keys = a_set ^ b_set > all_keys = a_set | b_set >>> a = dict.fromkeys("ab") >>> b = dict.fromkeys("bc") >>> a.viewkeys() - b.viewkeys() set(['a']) >>> a.viewkeys() & b.viewkeys() set(['b']) >>> a.viewkeys() ^ b.viewkeys() set(['a', 'c']) >>> a.viewkeys() | b.viewkeys() set(['a', 'c', 'b']) For 3.x replace viewkeys() with keys(). > It would save some space if I didn't have to duplicate all the keys > into sets (on the order of 10-100k small strings), instead being able > to directly perform the set-ops on the dicts. But otherwise, it was > pretty readable & straight-forward. > > -tkc