Path: csiph.com!x330-a1.tempe.blueboxinc.net!usenet.pasdenom.info!gegeweb.org!de-l.enfer-du-nord.net!feeder2.enfer-du-nord.net!feeds.phibee-telecom.net!newsfeed.xs4all.nl!newsfeed5.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; 'operator': 0.04; 'attributes': 0.05; 'attribute': 0.07; 'correspond': 0.07; 'dict': 0.09; 'dynamically': 0.09; 'am,': 0.12; 'def': 0.14; 'cc:addr :python-list': 0.15; 'subject:Generate': 0.16; 'cheers,': 0.18; 'wrote:': 0.18; 'instance': 0.18; 'key.': 0.18; 'specifies': 0.18; 'cc:no real name:2**0': 0.21; 'expanded': 0.23; 'header:In-Reply- To:1': 0.23; 'variable': 0.24; 'cc:2**0': 0.25; 'function': 0.27; 'import': 0.28; 'cc:addr:python.org': 0.29; 'message- id:@mail.gmail.com': 0.29; 'class': 0.29; 'received:209.85.214': 0.30; 'objects.': 0.30; 'received:mail-bw0-f46.google.com': 0.30; 'nov': 0.31; 'hi,': 0.31; 'determined': 0.32; 'wondering': 0.32; 'list': 0.32; 'there': 0.33; 'setting': 0.34; 'only)': 0.34; 'however,': 0.34; 'record': 0.35; 'regular': 0.35; 'beginning': 0.36; 'fri,': 0.36; 'instead.': 0.36; 'but': 0.37; 'received:google.com': 0.38; 'primary': 0.38; 'received:209.85': 0.38; 'called': 0.38; 'subject:: ': 0.39; 'might': 0.39; 'received:209': 0.40; 'store': 0.40; 'your': 0.61; '2011': 0.62; 'factory': 0.73; 'subject:Methods': 0.84 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc:content-type; bh=MWoPzfIdKBkAW6n7MEJXT7+yyX1lCCowTlTFjej1TxU=; b=JG44H/gl/fSi1sEa1JxdObZWz4F/DZ5JR0HB7cwc9aeWJ69kFU4sumd7svXJecJfTE 0eZNk+UNkVcrj+Hc/wt5gOhbtU79KihXCYaYUkAp63oK7h4zB/oPw5gSfNFL404oVjfL yi4kp2H85BHG1bKwCjIwFMjqtwqFczUtcK2ck= MIME-Version: 1.0 In-Reply-To: References: From: Ian Kelly Date: Fri, 18 Nov 2011 11:04:19 -0700 Subject: Re: Dynamically Generate Methods To: GZ Content-Type: text/plain; charset=ISO-8859-1 Cc: python-list@python.org 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: 31 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1321639492 news.xs4all.nl 6953 [2001:888:2000:d::a6]:54624 X-Complaints-To: abuse@xs4all.nl Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:15912 On Fri, Nov 18, 2011 at 7:51 AM, GZ wrote: > Hi, > > I have a class Record and a list key_attrs that specifies the names of > all attributes that correspond to a primary key. > > I can write a function like this to get the primary key: > > def get_key(instance_of_record): > return tuple(instance_of_record.__dict__[k] for k in key_attrs) > > However, since key_attrs are determined at the beginning of the > program while get_key() will be called over and over again, I am > wondering if there is a way to dynamically generate a get_ley method > with the key attributes expanded to avoid the list comprehension/ > generator. (Accidentally sent this to the OP only) This is exactly what the attrgetter factory function produces. from operator import attrgetter get_key = attrgetter(*key_attrs) But if your attribute names are variable and arbitrary, I strongly recommend you store them in a dict instead. Setting them as instance attributes risks that they might conflict with the regular attributes and methods on your objects. Cheers, Ian