Path: csiph.com!usenet.pasdenom.info!aioe.org!news.stack.nl!newsfeed.xs4all.nl!newsfeed1.news.xs4all.nl!xs4all!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail
Return-Path: <rosuav@gmail.com>
X-Original-To: python-list@python.org
Delivered-To: python-list@mail.python.org
X-Spam-Status: OK 0.005
X-Spam-Evidence: '*H*': 0.99; '*S*': 0.00; 'subsequent': 0.05; 'element': 0.07; 'assuming': 0.09; 'cc:addr:python-list': 0.11; 'jan': 0.12; '[none]': 0.16; 'discussion.': 0.16; 'elements,': 0.16; 'from:addr:rosuav': 0.16; 'from:name:chris angelico': 0.16; 'roy': 0.16; 'sentinel': 0.16; 'singleton': 0.16; 'subclass': 0.16; 'elements': 0.16; 'sat,': 0.16; 'wrote:': 0.18; 'have:': 0.19; 'example': 0.22; 'cc:addr:python.org': 0.22; 'cc:2**0': 0.24; 'shown': 0.26; 'header:In-Reply-To:1': 0.27; 'chris': 0.29; 'am,': 0.29; 'subject:list': 0.30; 'message-id:@mail.gmail.com': 0.30; 'usually': 0.31; 'post.': 0.31; 'trivial': 0.31; 'quite': 0.32; 'subject:with': 0.35; 'but': 0.35; 'received:google.com': 0.35; 'possible': 0.36; 'list': 0.37; 'minimum': 0.38; 'ahead': 0.38; 'expect': 0.39; 'does': 0.39; 'space': 0.40; 'most': 0.60; 'maximum': 0.63; 'smith': 0.68; 'article': 0.77; 'filling': 0.78; 'to:none': 0.92
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:cc :content-type; bh=bOrzwMspAdYdhQUImG6E+7dp5TSVhWh4PCClDAEwSuA=; b=hjG2QcP+hfy8Mj2ZBAKVTZyLfUqbeOcajhjE3WYGEW1Rxz7I6K3G7dO+c3t1SPneGW RFegr3lKSMO8zmqSeQdhHxAvb66lZtIL4YbcREy7Ano9ViE9kJHUIPsqgZV0Jj6A3Zcq +YrYaklgC8NOkXoDu83ITOS5cmbrhN/alpw7h3CNZZfnigMTelqmoL3DcpUEw+e7UcO/ 9kd3kGnBKsJ5Pa/cW727N+C/GN03g+I8W2dwzbvtrvXoK+Vlx8xZrYnYE7onYdNyevVO KiNM/Y49DOstROxxih7Y31H4zBOUiwt5WZvKItkEvEYEpWwmo+X/gNhdfzFByfSNovlM eqeg==
MIME-Version: 1.0
X-Received: by 10.66.129.133 with SMTP id nw5mr49764226pab.98.1388764676701; Fri, 03 Jan 2014 07:57:56 -0800 (PST)
In-Reply-To: <roy-6F59F6.10514703012014@news.panix.com>
References: <CACwCsY5P47-dB1NLQTUTQ=0aF6B+-M3y4hCxcUGmcVmHM8=-xQ@mail.gmail.com> <mailman.4853.1388763434.18130.python-list@python.org> <roy-6F59F6.10514703012014@news.panix.com>
Date: Sat, 4 Jan 2014 02:57:56 +1100
Subject: Re: Creating a list with holes
From: Chris Angelico <rosuav@gmail.com>
Cc: "python-list@python.org" <python-list@python.org>
Content-Type: text/plain; charset=UTF-8
X-BeenThere: python-list@python.org
X-Mailman-Version: 2.1.15
Precedence: list
List-Id: General discussion list for the Python programming language <python-list.python.org>
List-Unsubscribe: <https://mail.python.org/mailman/options/python-list>, <mailto:python-list-request@python.org?subject=unsubscribe>
List-Archive: <http://mail.python.org/pipermail/python-list/>
List-Post: <mailto:python-list@python.org>
List-Help: <mailto:python-list-request@python.org?subject=help>
List-Subscribe: <https://mail.python.org/mailman/listinfo/python-list>, <mailto:python-list-request@python.org?subject=subscribe>
Newsgroups: comp.lang.python
Message-ID: <mailman.4859.1388764686.18130.python-list@python.org>
Lines: 23
NNTP-Posting-Host: 2001:888:2000:d::a6
X-Trace: 1388764686 news.xs4all.nl 2976 [2001:888:2000:d::a6]:50606
X-Complaints-To: abuse@xs4all.nl
Xref: csiph.com comp.lang.python:63070

On Sat, Jan 4, 2014 at 2:51 AM, Roy Smith <roy@panix.com> wrote:
> In article <mailman.4853.1388763434.18130.python-list@python.org>,
>  Chris Angelico <rosuav@gmail.com> wrote:
>
>> Alternatively, if you expect to fill in most of the elements, it's
>> possible you'd be happier working with a subclass of list that
>> auto-expands by filling in the spare space with a singleton meaning
>> "no element here".
>
> And, if you know ahead of time the maximum number of elements you will
> ever have:
>
> x = [None] * max_count
>
> will preallocate them all with a minimum of fuss.

Yes, as I use in the trivial example in the subsequent post. But as a
general solution this is usually insufficient. (Whether or not None is
valid as a sentinel is, of course, quite orthogonal to the discussion.
I avoided assuming that it was, the OP's now shown that it does seem
to be.)

ChrisA