Path: csiph.com!usenet.pasdenom.info!news.redatomik.org!newsfeed.xs4all.nl!newsfeed2a.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 0.002 X-Spam-Evidence: '*H*': 1.00; '*S*': 0.00; 'list?': 0.07; 'advice.': 0.09; 'agree,': 0.09; 'received:80.91': 0.09; 'received:80.91.229': 0.09; 'received:gmane.org': 0.09; 'received:list': 0.09; 'wrong,': 0.09; 'def': 0.12; 'wrote': 0.14; 'carefully.': 0.16; "chris'": 0.16; 'cleaner': 0.16; 'code?': 0.16; 'gotcha.': 0.16; 'pythonic': 0.16; 'received:80.91.229.3': 0.16; 'received:plane.gmane.org': 0.16; 'skip:n 50': 0.16; 'tuple': 0.16; 'wrote:': 0.18; 'looked': 0.18; 'replacing': 0.19; 'thanks.': 0.20; 'code,': 0.22; "aren't": 0.24; 'looks': 0.24; 'pass': 0.26; 'header:X-Complaints-To:1': 0.27; 'idea': 0.28; 'leave': 0.29; 'is?': 0.30; 'work.': 0.31; 'code': 0.31; 'fri,': 0.33; 'could': 0.34; 'but': 0.35; 'thanks': 0.36; 'subject:?': 0.36; 'wrong': 0.37; 'list': 0.37; 'e.g.': 0.38; 'to:addr:python- list': 0.38; 'list,': 0.38; 'pm,': 0.38; 'little': 0.38; 'does': 0.39; 'to:addr:python.org': 0.39; 'received:org': 0.40; 'how': 0.40; 'read': 0.60; 'more': 0.64; 'situation': 0.65; 'frank': 0.68; 'subject:this': 0.83; '2015': 0.84; 'joel': 0.91; 'convinced': 0.93 X-Injected-Via-Gmane: http://gmane.org/ To: python-list@python.org From: "Frank Millman" Subject: Re: Is this unpythonic? Date: Fri, 8 May 2015 12:53:19 +0200 References: <554c8b0a$0$12992$c3e8da3$5496439d@news.astraweb.com> X-Gmane-NNTP-Posting-Host: 197.86.223.132 X-MSMail-Priority: Normal X-Newsreader: Microsoft Outlook Express 6.00.3790.4657 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.3790.4913 X-RFC2646: Format=Flowed; Original X-BeenThere: python-list@python.org X-Mailman-Version: 2.1.20+ 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: 54 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1431082398 news.xs4all.nl 2865 [2001:888:2000:d::a6]:56591 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:90138 "Steven D'Aprano" wrote in message news:554c8b0a$0$12992$c3e8da3$5496439d@news.astraweb.com... > On Fri, 8 May 2015 06:01 pm, Frank Millman wrote: > >> Hi all >> [...] >> >> However, every time I look at my own code, and I see "def x(y, z=[]): >> ....." it looks wrong because I have been conditioned to think of it as >> a gotcha. > > It is a gotcha, and a code smell. > > http://www.joelonsoftware.com/articles/Wrong.html > Interesting read - thanks. > You can use it, but with care: code smells aren't necessarily wrong, they > just need to be looked at a little more carefully. > > >> Would it be more pythonic to change them all to use the alternative >> "z=None", or is it ok to leave it as it is? Or to phrase it differently, >> how would an experienced pythonista react on seeing this when reviewing >> my >> code? > > I would change it to z=None *unless* you actually required the list to be > mutated, e.g. if you were using it as a cache. > Ok, you and Joel have convinced me. I will change it to z=None. > Does z have to be a list? Could you use an empty tuple instead? > > def x(y, z=()): ... > That was Chris' suggestion as well (thanks Chris). The idea appealed to me, but then I found a situation where I pass in a dictionary instead of a list, so that would not work. Replacing them all with None is cleaner and, I now agree, more pythonic. Thanks for the good advice. Frank