Path: csiph.com!v102.xanadu-bbs.net!xanadu-bbs.net!news.glorb.com!newsfeed.xs4all.nl!newsfeed1.news.xs4all.nl!xs4all!newsgate.cistron.nl!newsgate.news.xs4all.nl!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; 'needed,': 0.07; 'none:': 0.07; 'happens.': 0.09; 'processing,': 0.09; 'received:80.91': 0.09; 'received:80.91.229': 0.09; 'received:gmane.org': 0.09; 'received:list': 0.09; 'url:blog': 0.10; 'api': 0.11; 'python': 0.11; 'jan': 0.12; 'article:': 0.16; 'empty,': 0.16; 'finney': 0.16; 'iterable': 0.16; 'iterable,': 0.16; 'received:80.91.229.3': 0.16; 'received:plane.gmane.org': 0.16; 'reedy': 0.16; 'wrote:': 0.18; 'result.': 0.19; 'python?': 0.22; 'header:User-Agent:1': 0.23; 'values': 0.27; 'header:X-Complaints-To:1': 0.27; 'header :In-Reply-To:1': 0.27; 'function': 0.29; 'testing': 0.29; 'am,': 0.29; 'array': 0.29; "i'm": 0.30; 'url:05': 0.31; 'yes.': 0.31; 'link.': 0.33; 'not.': 0.33; 'subject: (': 0.35; 'curious': 0.36; 'subject:one': 0.36; 'requirements': 0.37; 'being': 0.38; 'sometimes': 0.38; 'thank': 0.38; 'ben': 0.38; 'follows:': 0.38; 'to:addr:python-list': 0.38; 'list,': 0.38; 'pm,': 0.38; 'does': 0.39; 'received:71': 0.39; 'to:addr:python.org': 0.39; 'received:org': 0.40; 'even': 0.60; 'mentioned': 0.61; 'no.': 0.61; 'here': 0.66; 'improvements': 0.68; 'special': 0.74; 'article': 0.77; 'received:fios.verizon.net': 0.84; 'url:2007': 0.84; 'demand': 0.91 X-Injected-Via-Gmane: http://gmane.org/ To: python-list@python.org From: Terry Reedy Subject: Re: one to many (passing variables) Date: Mon, 28 Jul 2014 15:29:04 -0400 References: <8561innkmw.fsf@benfinney.id.au> <53D308CB.8030900@cdreimer.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Gmane-NNTP-Posting-Host: pool-71-175-90-87.phlapa.fios.verizon.net User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:24.0) Gecko/20100101 Thunderbird/24.6.0 In-Reply-To: <53D308CB.8030900@cdreimer.com> 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: 42 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1406575758 news.xs4all.nl 2865 [2001:888:2000:d::a6]:40623 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:75321 On 7/25/2014 9:47 PM, C.D. Reimer wrote: > > On 7/24/2014 2:58 AM, Ben Finney wrote: >> Here is an article on good API design; the principles apply to Python >> . >> You know your API and its requirements better than we; see whether that >> sheds any light on improvements to make. > Thank you for the link. I'm curious about one item mentioned in the > article: "Avoid return values that Demand Exceptional Processing: return > zero-length array or empty collection, not null" > > Isn't a zero-length array, empty collection and null all the same thing? No. [] is an empty list, None is a null. > Or does the "Demand Exceptional Processing" comes from testing to see if > the object is empty versus being null? Testing whether null or not. > And does this apply to Python? Yes. If a function always returns a iterable, sometimes empty, it can be used as follows: for item in f(): process(item) If the iterable is empty, nothing happens. If the function returns None instead of empty, then the use has to write the following to get the same result. result = f() if result is not None: for item in f(): process(item) The function user may *elect* to give special processing to empty iterables. A None return *demands* special processing, even if not needed, as above. -- Terry Jan Reedy