Path: csiph.com!usenet.pasdenom.info!news.redatomik.org!newsfeed.xs4all.nl!newsfeed2a.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 0.001 X-Spam-Evidence: '*H*': 1.00; '*S*': 0.00; '(of': 0.07; '[1,': 0.09; 'identifier': 0.09; 'received:80.91': 0.09; 'received:80.91.229': 0.09; 'received:gmane.org': 0.09; 'received:list': 0.09; 'sentence': 0.09; 'subject: [': 0.09; 'terms,': 0.09; 'worse': 0.09; 'python': 0.11; 'jan': 0.12; 'identifiers': 0.16; 'received:80.91.229.3': 0.16; 'received:plane.gmane.org': 0.16; 'reedy': 0.16; 'weird': 0.16; 'student': 0.16; 'wrote:': 0.18; 'header:User-Agent:1': 0.23; 'club': 0.24; 'equivalent': 0.26; 'gets': 0.27; 'header:X-Complaints-To:1': 0.27; 'header:In-Reply- To:1': 0.27; 'point': 0.28; 'am,': 0.29; 'sets': 0.30; 'usually': 0.31; 'lists': 0.32; 'this.': 0.32; 'another': 0.32; 'subject:time': 0.33; 'problem': 0.35; "can't": 0.35; 'something': 0.35; "he's": 0.36; 'subject:List': 0.36; 'members.': 0.37; 'list': 0.37; 'level': 0.37; 'subject:]': 0.38; 'to:addr:python- list': 0.38; 'to:addr:python.org': 0.39; 'received:org': 0.40; 'how': 0.40; 'even': 0.60; 'read': 0.60; 'identify': 0.61; 'refer': 0.63; 'physical': 0.72; 'received:fios.verizon.net': 0.84; 'versions)': 0.84 X-Injected-Via-Gmane: http://gmane.org/ To: python-list@python.org From: Terry Reedy Subject: Re: List semantics [was Re: Slices time complexity] Date: Wed, 20 May 2015 14:42:08 -0400 References: <9ceklad15llnv3npejq9iuh91soci8aeqo@4ax.com> <7ea01590-a559-46e5-abf5-29622e39aae7@googlegroups.com> <555ac697$0$12910$c3e8da3$5496439d@news.astraweb.com> <862693ca-42cf-4f5b-ac12-133e43e7606b@googlegroups.com> <878uclf3bt.fsf@elektro.pacujo.net> <555af171$0$12995$c3e8da3$5496439d@news.astraweb.com> <874mn9ezaw.fsf@elektro.pacujo.net> <555b2fa9$0$12996$c3e8da3$5496439d@news.astraweb.com> <87oalfooz7.fsf@elektro.pacujo.net> <92992653-d511-4e33-a21d-541eeda4799b@googlegroups.com> <555c225b$0$2769$c3e8da3$76491128@news.astraweb.com> <28bca3fb-653d-40fb-9944-d28b01e77244@googlegroups.com> <555c368c$0$12906$c3e8da3$5496439d@news.astraweb.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit X-Gmane-NNTP-Posting-Host: pool-98-114-97-173.phlapa.fios.verizon.net User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 In-Reply-To: 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: 29 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1432147346 news.xs4all.nl 2845 [2001:888:2000:d::a6]:41154 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:90974 On 5/20/2015 4:54 AM, Gregory Ewing wrote: > At this point the student thinks, "Um... what? How > can an object contain another object *twice*?" > If he's still thinking in physical terms, this > sentence is nonsensical. > > It gets even worse with: > > x = [1, 2] > x[1] = x > > Now you have to say that the list contains *itself* > in some weird Tardis-like fashion! > > I can't think of any way to dispel the confusion > verbally without using some word like "reference" > or "pointer" or something with an equivalent meaning. > Something that suggests a level of indirectness. Python sets and lists (and frozen versions) are like clubs. A club roster contains identifiers that refer to and identify the members. Kids who can read and write names usually have no problem with this. The roster for the Recursive Club (of recursive clubs) would contain the identifier 'Recursive Club'. -- Terry Jan Reedy