Path: csiph.com!x330-a1.tempe.blueboxinc.net!usenet.pasdenom.info!aioe.org!feeder.news-service.com!news2.euro.net!newsfeed.xs4all.nl!newsfeed6.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 0.001 X-Spam-Evidence: '*H*': 1.00; '*S*': 0.00; 'wed,': 0.03; 'assign': 0.04; 'cant': 0.09; 'mutable': 0.09; 'object.': 0.09; 'tuple.': 0.09; 'pm,': 0.10; '>>>': 0.12; 'wrote:': 0.14; 'immutable': 0.16; 'methods,': 0.16; 'cc:addr:python-list': 0.17; 'object,': 0.19; 'received:74.125.82.44': 0.19; 'received:mail-ww0-f44.google.com': 0.19; 'header:In-Reply-To:1': 0.21; 'cc:2**0': 0.22; 'cc:no real name:2**0': 0.23; 'pointed': 0.25; 'object': 0.26; 'message- id:@mail.gmail.com': 0.28; 'changing': 0.28; 'needed,': 0.29; 'subject:?': 0.29; 'affected': 0.29; 'cc:addr:python.org': 0.30; 'tuples': 0.30; 'changes': 0.30; 'change.': 0.32; 'pointing': 0.32; 'someone': 0.33; 'list': 0.33; 'points': 0.34; 'however,': 0.34; 'using': 0.35; 'actual': 0.36; 'received:google.com': 0.37; 'change': 0.37; 'element': 0.37; 'case': 0.37; 'received:74.125.82': 0.38; 'received:74.125': 0.38; 'but': 0.38; 'data': 0.38; 'subject:: ': 0.38; '[1,2]': 0.84 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:in-reply-to:references:from:date :message-id:subject:to:cc:content-type; bh=YKalKGyKfCJup2eK0tKWuXjtB44LCVXyZvI3czOw5iI=; b=CW3zjvpvmBpZU8YrYSBApvhhmtlOXKBCCN6Kv6xVYioIiqA6F5WDDfJY1sowbe4gF5 KMBinW+tIU4YS6evKkZkd0wihRtLqEiajmRo4OjMMOKETHaipxyX0cM3gXKOI8H0R3LT lSLnFzCnAn0UAUTHW7f4z2QayRyY+w8e079bc= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc:content-type; b=ABAh+MpJ+pM4th3YL44cThTC7+pBVFk1TkfhyKQoT1/YXCgB7EIdEblShkMzHYn1BI cPyYWzyVANUoQXc2Xljl2baPoYZNKTekcUYDJ8LWvZgLvmBXcGrNm41nlbwBpeFCnQGJ VwimGcz9E46PyglxzF/EzMXceAAbAPOXvc40k= MIME-Version: 1.0 In-Reply-To: References: From: Noah Hall Date: Wed, 22 Jun 2011 16:58:50 +0100 Subject: Re: what happens inside? To: Chetan Harjani 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: 26 NNTP-Posting-Host: 82.94.164.166 X-Trace: 1308758352 news.xs4all.nl 49176 [::ffff:82.94.164.166]:33091 X-Complaints-To: abuse@xs4all.nl Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:8221 On Wed, Jun 22, 2011 at 4:45 PM, Chetan Harjani wrote: > why tuples are immutable whereas list are mutable? Because an immutable data type was needed, and a mutable type was also needed ;) > why when we do x=y where y is a list and then change a element in x, y > changes too( but the same is not the case when we change the whole value in > x ), whereas, in tuples when we change x, y is not affected and also we cant > change each individual element in tuple. Someone please clarify. That's because y points to an object. When you assign x = y, you say "assign name x to object that's also pointed to by name y". When you change the list using list methods, you're changing the actual object. Since x and y both point to the same object, they both change. However, if you then assign y = [1], name y no longer points to the original object. x still remains pointing to the original object. >>> a = [1,2] # assign name a to object [1,2] >>> b = a # assign name b to object referred to by name a >>> b [1, 2] >>> a = [3,4] # assign name a to object [3,4] >>> b [1, 2] >>> a [3, 4]