Path: csiph.com!usenet.pasdenom.info!dedibox.gegeweb.org!gegeweb.eu!nntpfeed.proxad.net!proxad.net!feeder1-1.proxad.net!ecngs!feeder2.ecngs.de!newsfeed.freenet.ag!news2.euro.net!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 0.017
X-Spam-Evidence: '*H*': 0.97; '*S*': 0.00; 'part,': 0.09; 'subject:()': 0.09; '"good': 0.16; 'constructs': 0.16; 'from:addr:rosuav': 0.16; 'from:name:chris angelico': 0.16; 'oct': 0.16; 'operation.': 0.16; 'readability.': 0.16; 'subject:array': 0.16; 'mon,': 0.16; 'wrote:': 0.17; 'header:In-Reply-To:1': 0.25; 'andrew': 0.27; 'message-id:@mail.gmail.com': 0.27; 'concern': 0.29; 'usually': 0.30; 'quickly': 0.32; 'cases,': 0.33; 'curious': 0.33; 'to:addr:python-list': 0.33; 'received:google.com': 0.34; 'whatever': 0.35; 'compared': 0.35; 'faster': 0.35; 'pm,': 0.35; 'received:209.85': 0.35; 'should': 0.36; 'received:209': 0.37; 'subject:: ': 0.38; 'performance': 0.39; 'to:addr:python.org': 0.39; 'header:Received:5': 0.40; 'your': 0.60; 'most': 0.61; 'yourself': 0.77
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:to :content-type; bh=t64afO6hTXL/L1EXLQHoZPchV/o6PZQ7bG+Zh+y1yRw=; b=IOO5Fo7JyTqcHbiAqz+N5/h5jh1xTrkcomipszs2txI736KTlvF/SjWG4iFckbwpFo PoR+XAZJi5gM4/6s8tnonoo1Aov3w2t7hjOB5cQD6LhkYwJ/R5cJEBNtoEVNMrw2zjv4 eZwWYWmCUzP4i9cARyotP2vez7BM1neFMJrEqA63+RdW29xk+q6B6DJKUmL+xSUmnkwe TgyrTZs/iO89tonfK23J19r4g9A4LBmxdUaN1U7fWuzUIZS03+s5aoQcAmR1Yer/uznL mhEbWku06pAaBHiqLWG3QiopiUSE9HU74hnHyIKWZi5cuCRybzlnRLT4VB+S9h3SDBn+ ftHA==
MIME-Version: 1.0
In-Reply-To: <508E0B72.7040107@r3dsolutions.com>
References: <6998a955-7b34-4f4f-b8d6-62d1028f7561@googlegroups.com> <mailman.2986.1351482209.27098.python-list@python.org> <4c024364-84df-403b-8b9e-4a4c8f06121c@googlegroups.com> <mailman.2991.1351484760.27098.python-list@python.org> <cd108b9d-e951-463e-8e50-a5a024a27c7f@googlegroups.com> <508e6649$0$29967$c3e8da3$5496439d@news.astraweb.com> <CAPTjJmpKhfKq+1OUOfNAQUsx5s6OZ8qBXcFcwkYDq4=YJy5i4w@mail.gmail.com> <508E0B72.7040107@r3dsolutions.com>
Date: Mon, 29 Oct 2012 23:40:53 +1100
Subject: Re: Negative array indicies and slice()
From: Chris Angelico <rosuav@gmail.com>
To: python-list@python.org
Content-Type: text/plain; charset=ISO-8859-1
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: <http://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: <http://mail.python.org/mailman/listinfo/python-list>, <mailto:python-list-request@python.org?subject=subscribe>
Newsgroups: comp.lang.python
Message-ID: <mailman.3006.1351514456.27098.python-list@python.org>
Lines: 18
NNTP-Posting-Host: 2001:888:2000:d::a6
X-Trace: 1351514456 news.xs4all.nl 6892 [2001:888:2000:d::a6]:33638
X-Complaints-To: abuse@xs4all.nl
Xref: csiph.com comp.lang.python:32366

On Mon, Oct 29, 2012 at 3:52 PM, Andrew Robinson
<andrew3@r3dsolutions.com> wrote:
> I am curious as to how quickly it constructs the result compared to a slice
> operation.
>
> Eg:
> a[1:5]
> vs.
> [ a[i] for i in xrange[1:5] ]

For the most part, don't concern yourself with performance. Go with
functionality and readability. In the trivial case shown here, the
slice is WAY clearer, so it should definitely be the one used; in
other cases, the slice might simply be insufficient, so you go with
whatever achieves your goal. Performance will usually be "good
enough", even if there's a marginally faster way.

ChrisA