Path: csiph.com!usenet.pasdenom.info!news.redatomik.org!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 0.003 X-Spam-Evidence: '*H*': 0.99; '*S*': 0.00; 'list?': 0.07; 'result,': 0.07; 'string': 0.09; 'iterate': 0.09; 'posting.': 0.09; 'received:80.91': 0.09; 'received:80.91.229': 0.09; 'received:gmane.org': 0.09; 'received:list': 0.09; 'def': 0.12; 'assume': 0.14; 'wrote': 0.14; "wouldn't": 0.14; "chris'": 0.16; 'dictionaries': 0.16; 'dictionary,': 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; 'unlike': 0.19; '>>>': 0.22; 'exists': 0.24; 'instead.': 0.24; 'sorry,': 0.24; 'pass': 0.26; 'values': 0.27; 'header:X-Complaints-To:1': 0.27; 'idea': 0.28; 'testing': 0.29; 'work.': 0.31; '>>>>': 0.31; 'keys': 0.31; 'probably': 0.32; 'worked': 0.33; 'fri,': 0.33; 'could': 0.34; 'operations': 0.35; 'test': 0.35; 'but': 0.35; 'there': 0.35; 'really': 0.36; 'subject:?': 0.36; 'should': 0.36; 'changing': 0.37; 'two': 0.37; 'list.': 0.37; 'work?': 0.38; 'needed': 0.38; 'to:addr:python-list': 0.38; 'list,': 0.38; 'pm,': 0.38; 'does': 0.39; 'to:addr:python.org': 0.39; 'received:org': 0.40; 'decided': 0.64; 'more': 0.64; 'situation': 0.65; 'here': 0.66; 'frank': 0.68; 'default': 0.69; 'subject:this': 0.83; '2015': 0.84; 'cough,': 0.84; 'trick,': 0.84 X-Injected-Via-Gmane: http://gmane.org/ To: python-list@python.org From: "Frank Millman" Subject: Re: Is this unpythonic? Date: Sat, 9 May 2015 08:51:40 +0200 References: <554c8b0a$0$12992$c3e8da3$5496439d@news.astraweb.com> <554cd119$0$12977$c3e8da3$5496439d@news.astraweb.com> X-Gmane-NNTP-Posting-Host: 197.89.68.193 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; Response 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: 63 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1431154310 news.xs4all.nl 2868 [2001:888:2000:d::a6]:40205 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:90214 "Frank Millman" wrote in message news:mik7j6$59n$1@ger.gmane.org... > > "Steven D'Aprano" wrote in message > news:554cd119$0$12977$c3e8da3$5496439d@news.astraweb.com... >> On Fri, 8 May 2015 08:53 pm, Frank Millman wrote: >> >>>> 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. >> >> >> Why wouldn't it work? If it worked with an empty list, it will probably >> work >> with an empty tuple instead. >> > > Sorry, I should have been more explicit. In the case of a dictionary, I > used 'def x(y, z={}' > > I have not checked, but I assume that as dictionaries are mutable, this > suffers from the same drawback as a default list. > > Unlike a list, it cannot be replaced by an empty tuple without changing > the body of the function. > > Dave's suggestion would have worked here - > > EMPTY_LIST = [] > EMPTY_DICT = {} > > But as I have decided to use the None trick, I use it for a default > dictionary as well. > Cough, cough, I really should have given that a moment's thought before posting. It just dawned on me that a dictionary *can* be replaced by an empty tuple without changing the body of the function. There are two operations I might perform on the dictionary - 1. iterate over the keys and retrieve the values 2: use 'in' to test if a given string exists as a key Both of these operations will work on a tuple and give the desired result, so it is a very valid workaround. More testing needed ... Frank