Path: csiph.com!v102.xanadu-bbs.net!xanadu-bbs.net!feeder.erje.net!eu.feeder.erje.net!news.stack.nl!newsfeed.xs4all.nl!newsfeed1.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; 'else:': 0.03; 'operator': 0.03; 'elif': 0.05; 'advocate': 0.07; 'explicit': 0.07; 'expressions': 0.07; 'mess': 0.09; 'pep': 0.09; 'received:80.91': 0.09; 'received:80.91.229': 0.09; 'received:gmane.org': 0.09; 'received:list': 0.09; 'subject:skip:a 10': 0.09; 'python': 0.11; 'jan': 0.12; 'suggest': 0.14; 'chained': 0.16; 'conditional': 0.16; 'expression.': 0.16; 'received:80.91.229.3': 0.16; 'received:plane.gmane.org': 0.16; 'reedy': 0.16; 'refactoring': 0.16; 'ternary': 0.16; 'language': 0.16; 'wrote:': 0.18; 'discussion': 0.18; 'header:User-Agent:1': 0.23; 'regardless': 0.24; 'header:X-Complaints-To:1': 0.27; 'header:In-Reply-To:1': 0.27; 'tim': 0.29; 'strongly': 0.30; 'chase': 0.31; "i'd": 0.34; 'could': 0.34; 'created': 0.35; 'similar': 0.36; 'being': 0.38; 'to:addr:python-list': 0.38; 'pm,': 0.38; 'ability': 0.39; 'to:addr:python.org': 0.39; 'received:org': 0.40; 'according': 0.40; 'expression': 0.60; 'received:173': 0.61; 'first': 0.61; 'making': 0.63; 'such': 0.63; 'more': 0.64; 'received:fios.verizon.net': 0.84 X-Injected-Via-Gmane: http://gmane.org/ To: python-list@python.org From: Terry Reedy Subject: Re: Ternary operator associativity Date: Thu, 06 Mar 2014 15:15:34 -0500 References: <20140306125958.31e096f8@bigbox.christie.dr> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Gmane-NNTP-Posting-Host: pool-173-75-254-207.phlapa.fios.verizon.net User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:24.0) Gecko/20100101 Thunderbird/24.3.0 In-Reply-To: <20140306125958.31e096f8@bigbox.christie.dr> 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: 44 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1394136963 news.xs4all.nl 2893 [2001:888:2000:d::a6]:41093 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:67949 On 3/6/2014 1:59 PM, Tim Chase wrote: > On 2014-03-06 03:34, candide wrote: >> According to the official documentation, the ternary operator has >> left-to-right associativity >> >>>>> left_to_right = (0 if 1 else 0) if 0 else 1 >>>>> right_to_left = 0 if 1 else (0 if 0 else 1) > > I'd never want to rely on my own ability to remember the language > spec, so I strongly advocate for making it explicit with parens > regardless of what the language defines. And that's if I ever created > such a mess in the first place. If you have more than one pair of > conditional expressions in a single assignment, I'd suggest that it's > a code-smell that could use refactoring for clarity/disambiguity. It is intended and part of the PEP discussion that one be able to write chained conditional expression in Python x = (a1 if c1 else a2 if c2 else a3 if c3 else a4) without extra ()s, similar to what one can write in C (if I remember correctly) x = c1 ? a1 : c2 ? a2 : c3 ? a3 : a4 both being abbreviations for chained if-elses if c1: x = a1 elif c2: x = a2 elif c3: x = a3 else: x = a4 In all three cases, the conditions are evaluated in 1,2,3 order, each before the corresponding expression. -- Terry Jan Reedy