Path: csiph.com!x330-a1.tempe.blueboxinc.net!newsfeed.hal-mli.net!feeder1.hal-mli.net!weretis.net!feeder1.news.weretis.net!feeder.erje.net!newsfeed.xs4all.nl!newsfeed6.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; 'anyway': 0.03; 'else:': 0.03; 'generators': 0.09; 'none:': 0.09; 'tuple': 0.09; 'def': 0.15; '"none"': 0.16; '(modulo': 0.16; '-tkc': 0.16; 'from:addr:python.list': 0.16; 'from:addr:tim.thechases.com': 0.16; 'from:name:tim chase': 0.16; 'message- id:@tim.thechases.com': 0.16; 'received:70.251': 0.16; 'received:dsl.rcsntx.swbell.net': 0.16; 'received:rcsntx.swbell.net': 0.16; 'received:swbell.net': 0.16; 'subject: \n ': 0.16; 'subject:iterable': 0.16; 'wrote:': 0.16; 'cc:2**0': 0.22; 'header:In-Reply-To:1': 0.22; 'code.': 0.26; "i'm": 0.27; 'fact': 0.27; 'yield': 0.29; 'asking': 0.29; 'cc:addr:gmail.com': 0.30; 'none,': 0.30; 'subject:?': 0.31; 'error': 0.32; 'there': 0.33; 'to:addr:python-list': 0.33; "i've": 0.34; 'header:User-Agent:1': 0.34; 'checking': 0.34; 'integer': 0.34; 'object': 0.35; 'none': 0.37; 'something': 0.37; 'could': 0.38; 'signal': 0.38; 'subject:: ': 0.39; 'to:addr:python.org': 0.39; 'subject: (': 0.39; 'skip:d 20': 0.39; 'your': 0.61; 'custom': 0.61; 'roughly': 0.67; 'subject:are': 0.70; 'subject:you': 0.81; 'cur,': 0.84; 'no?': 0.84; 'subject:Best': 0.93 Date: Wed, 07 Sep 2011 19:01:33 -0500 From: Tim Chase User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.20) Gecko/20110826 Icedove/3.1.12 MIME-Version: 1.0 To: python-list@python.org Subject: Re: Best way to check that you are at the beginning (the end) of an iterable? References: <264a83d7-aa43-4e36-b39e-3e67488279b6@glegroupsg2000goo.googlegroups.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - boston.accountservergroup.com X-AntiAbuse: Original Domain - python.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - tim.thechases.com X-Source: X-Source-Args: X-Source-Dir: Cc: Laurent X-BeenThere: python-list@python.org X-Mailman-Version: 2.1.12 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: 47 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1315443772 news.xs4all.nl 2493 [2001:888:2000:d::a6]:60734 X-Complaints-To: abuse@xs4all.nl Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:12931 On 09/07/11 18:22, Laurent wrote: > Anyway I was just asking if there is something better than > enumerate. So the answer is no? The fact that I have to create > a tuple with an incrementing integer for something as simple > as checking that I'm at the head just sounds awfully > unpythonic to me. I've made various generators that are roughly (modulo edge-condition & error checking) something like def with_prev(it): prev = None for i in it: yield prev, i i = prev def with_next(it): prev = it.next() for i in it: yield prev, i prev = i yield prev, None which can then be used something like your original for cur, next in with_next(iterable): if next is None: do_something_with_last(cur) else: do_regular_stuff_with_non_last(cur) for prev, cur in with_prev(iterable): if prev is None: do_something_with_first(cur) else: do_something_with_others(cur) If your iterable can return None, you could create a custom object to signal the non-condition: NO_ITEM = object() and then use NO_ITEM in place of "None" in the above code. -tkc