Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.python > #66321

Re: Explanation of list reference

Path csiph.com!newsfeed.hal-mli.net!feeder3.hal-mli.net!newsfeed.hal-mli.net!feeder1.hal-mli.net!newsfeed.xs4all.nl!newsfeed1a.news.xs4all.nl!xs4all!post.news.xs4all.nl!not-for-mail
Return-Path <ian.g.kelly@gmail.com>
X-Original-To python-list@python.org
Delivered-To python-list@mail.python.org
X-Spam-Status OK 0.011
X-Spam-Evidence '*H*': 0.98; '*S*': 0.00; 'explicitly': 0.05; 'assignment': 0.07; 'modified': 0.07; 'modify': 0.07; 'modifying': 0.07; 'referring': 0.07; '[0,': 0.09; 'immutable': 0.09; 'objects,': 0.09; 'illustrates': 0.16; 'meanwhile,': 0.16; 'objects.': 0.16; 'subsequently': 0.16; 'wrote:': 0.18; 'variable': 0.18; 'trying': 0.19; 'feb': 0.22; 'appears': 0.22; 'example': 0.22; 'affects': 0.24; 'regardless': 0.24; 'second': 0.26; 'header:In-Reply-To:1': 0.27; 'am,': 0.29; 'subject:list': 0.30; 'message-id:@mail.gmail.com': 0.30; "i'm": 0.30; '(which': 0.31; 'code': 0.31; '>>>>': 0.31; 'reflected': 0.31; 'lists': 0.32; '(e.g.': 0.33; 'fri,': 0.33; 'not.': 0.33; 'case,': 0.35; 'received:google.com': 0.35; 'there': 0.35; '14,': 0.36; 'object,': 0.36; 'thanks': 0.36; 'two': 0.37; 'list': 0.37; 'list.': 0.37; 'lists.': 0.38; 'to:addr:python-list': 0.38; 'list,': 0.38; 'short': 0.38; 'explain': 0.39; 'does': 0.39; 'sure': 0.39; 'to:addr:python.org': 0.39; 'dave': 0.60; 'affect': 0.61; 'first': 0.61; 'name': 0.63; 'refer': 0.63; 'spam.': 0.64; 'different': 0.65; 'between': 0.67; 'response.': 0.68; 'other.': 0.75; '100': 0.79; '"spam"': 0.84; 'all;': 0.84
DKIM-Signature v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :content-type; bh=hK+PQhkoNutFVZz39zKJ4Z3lv62bEddKZCC6HIxFiVI=; b=YUX5jLi7r6wNsqfAQ7r3z/0Ra9jpjkEjXVnPzvfHQh5zvRZIfL9EHW4lxHtVP0ALig 6F2hF+XSCcNlvQpH0DfO83nn+9usSvx+2xLqi4wGyOXlx7jbVlyvZnjiZNDC5RgpSB29 Q+izRO/C4h7swQljQJFS2SKFZWm9lbT8xsEo9wTc1d+eXrHNSy5GKLTj4FLsm6yBDrA5 qVkp0WByoL2KF81OjHbnk61aSfWDRdbbQykYY5tG0NdKljokBjaYVj0Z8RUe2duBSyvQ SE2LHnZksFt7rsrnjQ6ZqhPcLzPUHz/gFQDVzFtE/G+mZg0PwBymdNmrKvhxzhjhdOdX Q91g==
X-Received by 10.68.75.9 with SMTP id y9mr11302178pbv.61.1392408811767; Fri, 14 Feb 2014 12:13:31 -0800 (PST)
MIME-Version 1.0
In-Reply-To <917ede6d-db7c-4a8c-8203-27677283776b@googlegroups.com>
References <13208de8-0f85-4e60-b059-dc087c8fda41@googlegroups.com> <qoteh35ft4q.fsf@ruuvi.it.helsinki.fi> <917ede6d-db7c-4a8c-8203-27677283776b@googlegroups.com>
From Ian Kelly <ian.g.kelly@gmail.com>
Date Fri, 14 Feb 2014 13:12:51 -0700
Subject Re: Explanation of list reference
To Python <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 <https://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 <https://mail.python.org/mailman/listinfo/python-list>, <mailto:python-list-request@python.org?subject=subscribe>
Newsgroups comp.lang.python
Message-ID <mailman.6933.1392408815.18130.python-list@python.org> (permalink)
Lines 50
NNTP-Posting-Host 2001:888:2000:d::a6
X-Trace 1392408815 news.xs4all.nl 2833 [2001:888:2000:d::a6]:52108
X-Complaints-To abuse@xs4all.nl
Xref csiph.com comp.lang.python:66321

Show key headers only | View raw

On Fri, Feb 14, 2014 at 11:54 AM, dave em <daveandem2000@gmail.com> wrote:
> Thanks for your quick response.  I'm still not sure we understand.  The code below illustrates the concept we are trying to understand.
>
> Case 1: Example of variable with a specific value from P 170 of IYOCGWP
>
>>>> spam = 42
>>>> cheese = spam
>>>> spam = 100
>>>> spam
> 100
>>>> cheese
> 42
>
> Case 2: Example of variable with a list reference from p 170
>
>>>> spam = [0, 1, 2, 3, 4, 5]
>>>> cheese = spam
>>>> cheese[1] = 'Hello!'
>>>> spam
> [0, 'Hello!', 2, 3, 4, 5]
>>>> cheese
> [0, 'Hello!', 2, 3, 4, 5]
>
> What I am trying to explain is this, why in case 1 when acting on spam (changing the value from 42 to 100) only affects spam and not cheese.  Meanwhile, in case two acting on cheese also affects spam.

In the first case, after the assignment "cheese = spam", the names
spam and cheese are bound to the same object (42).  If you were to
modify the object 42 (which you cannot do in this case, because ints
are immutable) then you would see the change reflected in the object
regardless of which name you used to access it.  You then rebind the
name "spam" to a different object (100), which does not affect the
binding of the name "cheese" at all; the names end up referring to
different objects.

In the second case, after the assignment "cheese = spam", the names
again are bound to the same object, a list.  The assignment "cheese[1]
= 'Hello!'" then *modifies* that list, without rebinding cheese.
cheese and spam continue to refer to the same object, and since it was
modified you can see the change in that object regardless of which
name you used to access it.

If in the second case, you were to explicitly copy the list (e.g.
"cheese = list(spam)") prior to modifying it, then the two names would
instead be bound to different objects, and so subsequently modifying
one would not affect the other.

So the short answer is that there is no difference at all between the
way that names are bound to ints and the way they are bound to lists.
There only superficially appears to be a difference because ints are
immutable and lists are not.

Back to comp.lang.python | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Explanation of list reference dave em <daveandem2000@gmail.com> - 2014-02-14 10:08 -0800
  Re: Explanation of list reference Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2014-02-14 20:26 +0200
    Re: Explanation of list reference dave em <daveandem2000@gmail.com> - 2014-02-14 10:54 -0800
      Re: Explanation of list reference Denis McMahon <denismfmcmahon@gmail.com> - 2014-02-14 19:20 +0000
      Re: Explanation of list reference Marko Rauhamaa <marko@pacujo.net> - 2014-02-14 21:56 +0200
        Re: Explanation of list reference Ian Kelly <ian.g.kelly@gmail.com> - 2014-02-14 13:17 -0700
          Re: Explanation of list reference Marko Rauhamaa <marko@pacujo.net> - 2014-02-14 22:58 +0200
            Re: Explanation of list reference Chris Angelico <rosuav@gmail.com> - 2014-02-15 08:16 +1100
              Re: Explanation of list reference Marko Rauhamaa <marko@pacujo.net> - 2014-02-14 23:43 +0200
                Re: Explanation of list reference Ned Batchelder <ned@nedbatchelder.com> - 2014-02-14 19:00 -0500
                Re: Explanation of list reference dave em <daveandem2000@gmail.com> - 2014-02-14 16:26 -0800
                Re: Explanation of list reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-15 06:07 +0000
                Re: Explanation of list reference Marko Rauhamaa <marko@pacujo.net> - 2014-02-15 11:00 +0200
                Re: Explanation of list reference Chris Angelico <rosuav@gmail.com> - 2014-02-15 11:57 +1100
                Re: Explanation of list reference Rustom Mody <rustompmody@gmail.com> - 2014-02-14 17:55 -0800
                Re: Explanation of list reference Chris Angelico <rosuav@gmail.com> - 2014-02-15 13:08 +1100
                Re: Explanation of list reference Rustom Mody <rustompmody@gmail.com> - 2014-02-14 18:34 -0800
                Re: Explanation of list reference Chris Angelico <rosuav@gmail.com> - 2014-02-15 13:42 +1100
                Re: Explanation of list reference Rustom Mody <rustompmody@gmail.com> - 2014-02-14 19:14 -0800
                Re: Explanation of list reference Chris Angelico <rosuav@gmail.com> - 2014-02-15 14:33 +1100
                Re: Explanation of list reference Rustom Mody <rustompmody@gmail.com> - 2014-02-14 20:24 -0800
                Re: Explanation of list reference Chris Angelico <rosuav@gmail.com> - 2014-02-15 15:37 +1100
                Re: Explanation of list reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-15 06:54 +0000
                Re: Explanation of list reference Chris Angelico <rosuav@gmail.com> - 2014-02-15 18:19 +1100
                Re: Explanation of list reference Ian Kelly <ian.g.kelly@gmail.com> - 2014-02-14 22:20 -0700
                Re: Explanation of list reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-15 07:03 +0000
                Re: Explanation of list reference Chris Angelico <rosuav@gmail.com> - 2014-02-15 16:31 +1100
                Re: Explanation of list reference Rustom Mody <rustompmody@gmail.com> - 2014-02-14 22:07 -0800
                Re: Explanation of list reference Ben Finney <ben+python@benfinney.id.au> - 2014-02-15 17:19 +1100
                Re: Explanation of list reference Rustom Mody <rustompmody@gmail.com> - 2014-02-14 22:31 -0800
                Re: Explanation of list reference Chris Angelico <rosuav@gmail.com> - 2014-02-15 17:23 +1100
                Re: Explanation of list reference Ian Kelly <ian.g.kelly@gmail.com> - 2014-02-15 01:08 -0700
                Re: Explanation of list reference Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-02-15 12:42 +0000
                Re: Explanation of list reference Marko Rauhamaa <marko@pacujo.net> - 2014-02-15 15:44 +0200
                Re: Explanation of list reference Rustom Mody <rustompmody@gmail.com> - 2014-02-16 06:00 -0800
                Re: Explanation of list reference Ned Batchelder <ned@nedbatchelder.com> - 2014-02-16 11:29 -0500
                Re: Explanation of list reference Rustom Mody <rustompmody@gmail.com> - 2014-02-16 08:50 -0800
                Re: Explanation of list reference Marko Rauhamaa <marko@pacujo.net> - 2014-02-16 20:01 +0200
                Re: Explanation of list reference Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-02-16 18:36 +0000
                Re: Explanation of list reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-17 05:52 +0000
                Re: Explanation of list reference Terry Reedy <tjreedy@udel.edu> - 2014-02-15 15:40 -0500
                Re: Explanation of list reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-16 02:27 +0000
                Re: Explanation of list reference Grant Edwards <invalid@invalid.invalid> - 2014-02-15 19:02 +0000
                Re: Explanation of list reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-15 06:44 +0000
                Re: Explanation of list reference Chris Angelico <rosuav@gmail.com> - 2014-02-15 18:05 +1100
                Re: Explanation of list reference Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-02-16 00:29 +1300
                Re: Explanation of list reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-15 06:15 +0000
                Re: Explanation of list reference Rustom Mody <rustompmody@gmail.com> - 2014-02-14 22:24 -0800
                Re: Explanation of list reference Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-02-16 00:32 +1300
                Re: Explanation of list reference Chris Angelico <rosuav@gmail.com> - 2014-02-15 22:37 +1100
                Re: Explanation of list reference Marko Rauhamaa <marko@pacujo.net> - 2014-02-15 11:10 +0200
                Re: Explanation of list reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-15 10:31 +0000
                Re: Explanation of list reference Christian Gollwitzer <auriocus@gmx.de> - 2014-02-15 10:44 +0100
                Re: Explanation of list reference Marko Rauhamaa <marko@pacujo.net> - 2014-02-15 12:10 +0200
                Re: Explanation of list reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-15 10:53 +0000
                Re: Explanation of list reference Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-02-17 11:40 +1300
                Re: Explanation of list reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-17 05:57 +0000
                Re: Explanation of list reference Chris Angelico <rosuav@gmail.com> - 2014-02-15 22:21 +1100
                Re: Explanation of list reference Alister <alister.ware@ntlworld.com> - 2014-02-16 19:16 +0000
                Re: Explanation of list reference Ben Finney <ben+python@benfinney.id.au> - 2014-02-15 15:20 +1100
                Re: Explanation of list reference Marko Rauhamaa <marko@pacujo.net> - 2014-02-15 11:31 +0200
                Re: Explanation of list reference Marko Rauhamaa <marko@pacujo.net> - 2014-02-15 12:13 +0200
                Re: Explanation of list reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-15 11:17 +0000
                Re: Explanation of list reference Marko Rauhamaa <marko@pacujo.net> - 2014-02-15 14:07 +0200
                Re: Explanation of list reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-15 14:41 +0000
                Re: Explanation of list reference Marko Rauhamaa <marko@pacujo.net> - 2014-02-15 18:29 +0200
                Re: Explanation of list reference Roy Smith <roy@panix.com> - 2014-02-15 12:02 -0500
                Re: Explanation of list reference Rustom Mody <rustompmody@gmail.com> - 2014-02-15 09:30 -0800
                Re: Explanation of list reference Ian Kelly <ian.g.kelly@gmail.com> - 2014-02-15 11:37 -0700
                Re: Explanation of list reference Ian Kelly <ian.g.kelly@gmail.com> - 2014-02-15 11:45 -0700
                Re: Explanation of list reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-15 19:05 +0000
                Re: Explanation of list reference Ian Kelly <ian.g.kelly@gmail.com> - 2014-02-15 10:11 -0700
                Re: Explanation of list reference Marko Rauhamaa <marko@pacujo.net> - 2014-02-15 22:20 +0200
                Re: Explanation of list reference Ian Kelly <ian.g.kelly@gmail.com> - 2014-02-15 14:20 -0700
                Re: Explanation of list reference Rustom Mody <rustompmody@gmail.com> - 2014-02-15 09:47 -0800
                Re: Explanation of list reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-15 19:17 +0000
                Re: Explanation of list reference Marko Rauhamaa <marko@pacujo.net> - 2014-02-15 23:01 +0200
                Re: Explanation of list reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-16 02:25 +0000
                Re: Explanation of list reference Marko Rauhamaa <marko@pacujo.net> - 2014-02-16 13:18 +0200
                Re: Explanation of list reference Chris Angelico <rosuav@gmail.com> - 2014-02-15 22:31 +1100
                Re: Explanation of list reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-15 10:40 +0000
                Re: Explanation of list reference Chris Angelico <rosuav@gmail.com> - 2014-02-15 22:17 +1100
            Re: Explanation of list reference Marko Rauhamaa <marko@pacujo.net> - 2014-02-14 23:20 +0200
            Re: Explanation of list reference Marko Rauhamaa <marko@pacujo.net> - 2014-02-16 10:08 +0200
              Re: Explanation of list reference Ian Kelly <ian.g.kelly@gmail.com> - 2014-02-16 01:28 -0700
                Re: Explanation of list reference Marko Rauhamaa <marko@pacujo.net> - 2014-02-16 12:52 +0200
                Re: Explanation of list reference Chris Angelico <rosuav@gmail.com> - 2014-02-16 22:24 +1100
                Re: Explanation of list reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-16 12:04 +0000
                Re: Explanation of list reference Marko Rauhamaa <marko@pacujo.net> - 2014-02-16 18:17 +0200
              Re: Explanation of list reference Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2014-02-16 10:35 +0200
              Re: Explanation of list reference Ian Kelly <ian.g.kelly@gmail.com> - 2014-02-16 01:35 -0700
              Re: Explanation of list reference Alan Bawden <alan@scooby-doo.csail.mit.edu> - 2014-02-16 03:38 -0500
              Re: Explanation of list reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-16 08:40 +0000
                Re: Explanation of list reference Chris Angelico <rosuav@gmail.com> - 2014-02-16 21:18 +1100
              Re: Explanation of list reference Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2014-02-16 12:10 -0500
        Re: Explanation of list reference Ned Batchelder <ned@nedbatchelder.com> - 2014-02-14 15:45 -0500
      Re: Explanation of list reference Ian Kelly <ian.g.kelly@gmail.com> - 2014-02-14 13:12 -0700
      Re: Explanation of list reference Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2014-02-14 22:36 +0200
        Re: Explanation of list reference Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-02-16 01:03 +1300
        Re: Explanation of list reference Ben Finney <ben+python@benfinney.id.au> - 2014-02-15 23:21 +1100
  Re: Explanation of list reference Ned Batchelder <ned@nedbatchelder.com> - 2014-02-14 13:42 -0500
  Re: Explanation of list reference Ryan Gonzalez <rymg19@gmail.com> - 2014-02-14 12:31 -0600
    Re: Explanation of list reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-15 05:36 +0000
      Re: Explanation of list reference Chris Angelico <rosuav@gmail.com> - 2014-02-15 17:07 +1100
        Re: Explanation of list reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-15 06:48 +0000
          Re: Explanation of list reference Chris Angelico <rosuav@gmail.com> - 2014-02-15 17:57 +1100
            Re: Explanation of list reference Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-02-16 01:18 +1300
              Re: Explanation of list reference Chris Angelico <rosuav@gmail.com> - 2014-02-15 23:24 +1100
                Re: Explanation of list reference Marko Rauhamaa <marko@pacujo.net> - 2014-02-15 15:25 +0200
                Re: Explanation of list reference Ben Finney <ben+python@benfinney.id.au> - 2014-02-16 00:59 +1100
                Re: Explanation of list reference Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-02-17 11:54 +1300
                Re: Explanation of list reference Chris Angelico <rosuav@gmail.com> - 2014-02-17 10:02 +1100
                Re: Explanation of list reference Roy Smith <roy@panix.com> - 2014-02-16 18:46 -0500
                Re: Explanation of list reference Chris Angelico <rosuav@gmail.com> - 2014-02-17 12:26 +1100
                Re: Explanation of list reference Ben Finney <ben+python@benfinney.id.au> - 2014-02-17 10:05 +1100
                Re: Explanation of list reference Roy Smith <roy@panix.com> - 2014-02-16 18:43 -0500
                Re: Explanation of list reference Ben Finney <ben+python@benfinney.id.au> - 2014-02-17 11:04 +1100
                Re: Explanation of list reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-17 06:31 +0000
                Re: Explanation of list reference Rustom Mody <rustompmody@gmail.com> - 2014-02-17 05:43 -0800
                Re: Explanation of list reference Ned Batchelder <ned@nedbatchelder.com> - 2014-02-16 20:43 -0500
                Re: Explanation of list reference Chris Angelico <rosuav@gmail.com> - 2014-02-17 12:59 +1100
                Re: Explanation of list reference Roy Smith <roy@panix.com> - 2014-02-16 22:28 -0500
                Re: Explanation of list reference Ben Finney <ben+python@benfinney.id.au> - 2014-02-17 14:52 +1100
                Re: Explanation of list reference Rustom Mody <rustompmody@gmail.com> - 2014-02-16 20:35 -0800
                Re: Explanation of list reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-17 08:03 +0000
                Re: Explanation of list reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-17 06:21 +0000
                Re: Explanation of list reference Chris Angelico <rosuav@gmail.com> - 2014-02-17 18:11 +1100
                Re: Explanation of list reference Rotwang <sg552@hotmail.co.uk> - 2014-02-17 18:24 +0000
          Re: Explanation of list reference Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2014-02-15 14:30 -0500
  Re: Explanation of list reference Terry Reedy <tjreedy@udel.edu> - 2014-02-14 16:37 -0500
  Re: Explanation of list reference pecore@pascolo.net - 2014-02-14 23:34 +0100
  Re: Explanation of list reference Christian Gollwitzer <auriocus@gmx.de> - 2014-02-15 10:38 +0100
  Re: Explanation of list reference Ben Finney <ben+python@benfinney.id.au> - 2014-02-16 01:20 +1100
  Re: Explanation of list reference Chris Angelico <rosuav@gmail.com> - 2014-02-16 01:26 +1100
  Re: Explanation of list reference Joshua Landau <joshua@landau.ws> - 2014-02-15 20:44 +0000
  Re: Explanation of list reference Chris Angelico <rosuav@gmail.com> - 2014-02-16 09:27 +1100

csiph-web