Path: csiph.com!v102.xanadu-bbs.net!xanadu-bbs.net!feeder.erje.net!eu.feeder.erje.net!news.stack.nl!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; 'operator': 0.03; '(except': 0.07; 'binary': 0.07; '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; 'tests,': 0.09; 'jan': 0.12; 'comparisons,': 0.16; 'left,': 0.16; 'operators,': 0.16; 'operators.': 0.16; 'precedence': 0.16; 'precedence.': 0.16; 'received:80.91.229.3': 0.16; 'received:plane.gmane.org': 0.16; 'reedy': 0.16; 'ternary': 0.16; 'unary': 0.16; 'wrote:': 0.18; 'seems': 0.21; 'programming': 0.22; 'header:User-Agent:1': 0.23; 'section.': 0.24; 'compare': 0.26; 'header:X-Complaints-To:1': 0.27; 'header:In-Reply-To:1': 0.27; 'url:bugs': 0.29; 'am,': 0.29; 'evaluation': 0.30; 'specified': 0.30; '>>>>': 0.31; 'doc': 0.31; 'grouping': 0.31; 'operators': 0.31; 'url:python': 0.33; '"the': 0.34; 'could': 0.34; 'there': 0.35; 'false': 0.36; 'url:org': 0.36; 'to:addr:python-list': 0.38; 'skip:- 10': 0.38; 'to:addr:python.org': 0.39; 'received:org': 0.40; 'according': 0.40; 'chain': 0.60; 'received:173': 0.61; 'back': 0.62; 'skip:n 10': 0.64; 'behavior': 0.77; '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 13:52:46 -0500 References: 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: 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: 34 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1394131996 news.xs4all.nl 2918 [2001:888:2000:d::a6]:51388 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:67947 On 3/6/2014 6:34 AM, candide wrote: > According to the official documentation, the ternary operator has > left-to-right associativity : The proper terms is 'conditional expression', which goes back to "The C Programming Language" (K&R). There are many unary operators, many binary operators, and there could be other ternary operators. > ------------------- Operators in the same box group left to right > (except for comparisons, including tests, which all have the same > precedence and chain from left to right -- see section Comparisons -- > and exponentiation, which groups from right to left). > ------------------- > > Nevertheless, the ternary operator grouping seems to be from right to > left, compare : > >>>> p = 0 if 1 else 0 if 0 else 1 p > 0 >>>> left_to_right = (0 if 1 else 0) if 0 else 1 >>>> right_to_left = 0 if 1 else (0 if 0 else 1) >>>> p == left_to_right > False >>>> p == right_to_left > True This behavior is specified in the grammar as given in the C-E section. The doc is also inconsistent about evaluation order and precedence. I opened http://bugs.python.org/issue20859 . -- Terry Jan Reedy