Path: csiph.com!usenet.pasdenom.info!weretis.net!feeder4.news.weretis.net!rt.uk.eu.org!newsfeed.xs4all.nl!newsfeed3.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 0.013 X-Spam-Evidence: '*H*': 0.97; '*S*': 0.00; 'none:': 0.07; '__init__': 0.09; 'attributes': 0.09; 'form?': 0.09; 'subject:using': 0.09; 'python': 0.11; 'def': 0.12; 'attribute,': 0.16; 'attribute?': 0.16; 'fits': 0.16; 'foo(object):': 0.16; 'lazily': 0.16; 'subject:class': 0.16; 'subject:member': 0.16; 'sender:addr:gmail.com': 0.17; 'wrote:': 0.18; 'pfxlen:0': 0.19; 'saying': 0.22; 'header:User-Agent:1': 0.23; 'task': 0.26; 'this:': 0.26; 'certain': 0.27; 'header:In-Reply-To:1': 0.27; 'to:2**1': 0.27; 'wondering': 0.29; 'raise': 0.29; "doesn't": 0.30; 'fine,': 0.31; 'class': 0.32; 'skip:_ 10': 0.34; 'but': 0.35; 'received:google.com': 0.35; 'really': 0.36; 'two': 0.37; 'sometimes': 0.38; 'to:addr:python-list': 0.38; 'pm,': 0.38; 'to:addr:python.org': 0.39; 'voice': 0.60; 'matter': 0.61; 'hear': 0.63; 'to:addr:gmail.com': 0.65; 'between': 0.67; 'different.': 0.84; 'idiom': 0.84; 'situations,': 0.84; 'x):': 0.84; 'hand,': 0.93 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=sender:message-id:date:from:user-agent:mime-version:to:subject :references:in-reply-to:content-type:content-transfer-encoding; bh=B1NDl0malmniBLNYiJgoBEFmQjQ4WfeyCGavBhw/2bM=; b=neSIS5PRC71shOGKMOHVCj/lH60B0Whi9Ltedqt2+vNKVt2VxZjxWljY/fAIFVCZDG +MQUZxMIWFMlcnwD3KNSq4lqSP9eM59xXSPAb48/FlHxYvq9fYdOetS7DB50sziMQHRq RuCaQi+DG6g5ngjVCPXL+msAa2C3gCRpBVcocIdxlr2X0SPyHjRVOR/UVFCCoK5waq4a Q+MH9SZ1xddXxf4n+YqcN27KIZ/nBFFT1NOI5POel3lfV1HAh/6li9szV8rHUTLqIoxK 8mJnGp3Dr+QpFvOYJGmSIvyPlLmff3pPFGYshKRsal7Pkf2TLzg1dAjKOh0p6u9dT50c 88DQ== X-Received: by 10.224.80.4 with SMTP id r4mr13572507qak.69.1382219756717; Sat, 19 Oct 2013 14:55:56 -0700 (PDT) Sender: Ned Batchelder Date: Sat, 19 Oct 2013 17:55:57 -0400 From: Ned Batchelder User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.8; rv:24.0) Gecko/20100101 Thunderbird/24.0.1 MIME-Version: 1.0 To: Peter Cacioppi , python-list@python.org Subject: Re: skipping __init__ and using exploiting a class member instead References: In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit 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: 29 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1382219758 news.xs4all.nl 15878 [2001:888:2000:d::a6]:36681 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:57117 On 10/19/13 5:44 PM, Peter Cacioppi wrote: > Is the following considered poor Python form? > > class Foo (object) : > _lazy = None > def foo(self, x) : > _lazy = _lazy or self.get_something(x) > def get_something(self, x) : > # doesn't really matter > > I like this idiom for certain situations, just wondering if it will raise the hackles of other Pythonistas. > > I use this idiom sparingly, but sometimes it just fits the task at hand, I hear Guidos voice saying "use the Force" in my ear, etc. You present this as a choice between __init__ or a class attribute, but those two things are very different. Is your intent to have an instance attribute, or a class attribute? Lazily populated instance attributes are fine, I would do it like this: class Foo(object): def __init__(self): self._lazy = None def foo(self, x): if self._lazy is None: self._lazy = self.get_something(x) ... --Ned.