Path: csiph.com!usenet.pasdenom.info!news.albasani.net!newsfeed.freenet.ag!news2.euro.net!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail
Return-Path: <python-python-list@m.gmane.org>
X-Original-To: python-list@python.org
Delivered-To: python-list@mail.python.org
X-Spam-Status: OK 0.001
X-Spam-Evidence: '*H*': 1.00; '*S*': 0.00; 'expressions': 0.07; 'parameter': 0.07; 'subject:skip:c 10': 0.07; 'python': 0.09; 'received:80.91': 0.09; 'received:80.91.229': 0.09; 'received:gmane.org': 0.09; 'received:list': 0.09; 'references.': 0.09; 'stored': 0.10; "'at": 0.16; 'bind': 0.16; 'funcs': 0.16; 'helps.': 0.16; 'lambda': 0.16; 'message-id:@dough.gmane.org': 0.16; 'received:80.91.229.3': 0.16; 'received:plane.gmane.org': 0.16; 'simplest': 0.16; 'variable': 0.20; 'references': 0.23; 'this:': 0.23; 'header:In-Reply-To:1': 0.25; 'header:User- Agent:1': 0.26; 'header:X-Complaints-To:1': 0.28; 'subject:list': 0.28; 'print': 0.32; 'anyone': 0.33; 'to:addr:python-list': 0.33; 'received:org': 0.36; 'does': 0.37; 'subject:: ': 0.38; 'gives': 0.39; 'to:addr:python.org': 0.39; 'header:Received:5': 0.40; 'more': 0.63; 'importantly,': 0.65; 'received:93': 0.72; '(they': 0.84; 'received:hr': 0.84; 'why?': 0.84; 'subject:funny': 0.91
X-Injected-Via-Gmane: http://gmane.org/
To: python-list@python.org
From: =?UTF-8?B?SnVya28gR29zcG9kbmV0acSH?= <jurko.gospodnetic@pke.hr>
Subject: Re: lambda in list comprehension acting funny
Date: Wed, 11 Jul 2012 09:01:18 +0200
Organization: PKE sistemi d.o.o.
References: <CADjSo4QvTnGKy_ZYOO5qZu3tSKovwAMGjku4L+RXEkYmwXPz4g@mail.gmail.com> <CADjSo4SeuMJOP_iEM9rjVsFtVh84HaVUtPkUCZGKiEdQBWuerw@mail.gmail.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
X-Gmane-NNTP-Posting-Host: 93-139-12-146.adsl.net.t-com.hr
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:13.0) Gecko/20120614 Thunderbird/13.0.1
In-Reply-To: <CADjSo4SeuMJOP_iEM9rjVsFtVh84HaVUtPkUCZGKiEdQBWuerw@mail.gmail.com>
X-BeenThere: python-list@python.org
X-Mailman-Version: 2.1.12
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.2008.1341990101.4697.python-list@python.org>
Lines: 30
NNTP-Posting-Host: 2001:888:2000:d::a6
X-Trace: 1341990101 news.xs4all.nl 6872 [2001:888:2000:d::a6]:40629
X-Complaints-To: abuse@xs4all.nl
Xref: csiph.com comp.lang.python:25168

   Hi.

>> funcs = [ lambda x: x**i for i in range( 5 ) ]
>> print funcs[0]( 2 )
>>
>> This gives me
>> 16
>>
>> When I was excepting
>> 1
>>
>> Does anyone know why?

   Just the way Python lambda expressions bind their variable 
references. Inner 'i' references the outer scope's 'i' variable and not 
its value 'at the time the lambda got defined'.


> And more importantly, what's the simplest way to achieve the latter? :)

   Try giving the lambda a default parameter (they get calculated and 
have their value stored at the time the lambda is defined) like this:
   funcs = [ lambda x, i=i: x**i for i in range( 5 ) ]


   Hope this helps.

   Best regards,
     Jurko Gospodnetić