Re: Could you explain this rebinding (or some other action) on "nums = nums"?

Path	csiph.com!fu-berlin.de!uni-berlin.de!not-for-mail
From	Erik <python@lucidity.plus.com>
Newsgroups	comp.lang.python
Subject	Re: Could you explain this rebinding (or some other action) on "nums = nums"?
Date	Tue, 1 Dec 2015 22:34:13 +0000
Lines	19
Message-ID	<mailman.88.1449009296.14615.python-list@python.org> (permalink)
References	<94c2e42e-1e5f-40cf-9259-26035e277bf3@googlegroups.com> <mailman.37.1435191416.3674.python-list@python.org> <b48d4b38-a28a-4408-8271-f79e850f453f@googlegroups.com> <mailman.51.1448940760.14615.python-list@python.org> <n3l050$l7a$4@dont-email.me> <mailman.83.1449002726.14615.python-list@python.org> <n3l3vk$l7a$6@dont-email.me>
Mime-Version	1.0
Content-Type	text/plain; charset=windows-1252; format=flowed
Content-Transfer-Encoding	7bit
X-Trace	news.uni-berlin.de /R/Smm8h32f1sxC6fEUB2gxAWQgsKS1/CbDm/LvfCojA==
Return-Path	<python@lucidity.plus.com>
X-Original-To	python-list@python.org
Delivered-To	python-list@mail.python.org
X-Spam-Status	OK 0.012
X-Spam-Evidence	'H': 0.98; 'S': 0.00; 'assignment': 0.07; 'bug.': 0.07; 'augmented': 0.09; 'from:addr:python': 0.16; 'mechanism.': 0.16; 'mutated': 0.16; 'received:84.93': 0.16; 'received:84.93.230': 0.16; 'received:io': 0.16; 'received:psf.io': 0.16; 'subject:Could': 0.16; 'wrote:': 0.16; 'element': 0.18; 'to:2**1': 0.21; 'assign': 0.22; 'originally': 0.23; 'header:In-Reply-To:1': 0.24; 'header:User-Agent:1': 0.26; 'looks': 0.29; 'subject:other': 0.29; 'subject:some': 0.29; 'received:84': 0.32; 'subject:) ': 0.32; 'getting': 0.33; 'list': 0.34; 'asking': 0.35; 'but': 0.36; 'should': 0.36; 'assigned': 0.36; 'to:addr:python-list': 0.36; 'subject:: ': 0.37; 'being': 0.37; 'received:192': 0.39; 'to:addr:python.org': 0.40; 'charset:windows-1252': 0.62; 'fundamental': 0.66; 'denis': 0.84; 'subject:this': 0.85; 'subject:you': 0.85
X-CM-Score	0.00
X-CNFS-Analysis	v=2.1 cv=JN/GyJ+b c=1 sm=1 tr=0 a=Ypmeq7T0cKALDUsRPCToMg==:117 a=Ypmeq7T0cKALDUsRPCToMg==:17 a=0Bzu9jTXAAAA:8 a=EBOSESyhAAAA:8 a=N659UExz7-8A:10 a=z2vHlgiCS6V18mFbxW0A:9 a=pILNOxqGKmIA:10
User-Agent	Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0
In-Reply-To	<n3l3vk$l7a$6@dont-email.me>
X-BeenThere	python-list@python.org
X-Mailman-Version	2.1.20+
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>
Xref	csiph.com comp.lang.python:99824

Show key headers only | View raw

On 01/12/15 21:37, Denis McMahon wrote:
> The assignment succeeds. That's imo a bug. If it's a TypeError to try and
> assign a value to tup[1], then tup[1] should not allow the mutated list
> to be assigned.

Nothing got assigned.

That original list object remains in that slot. However, it has been 
mutated since it was originally assigned.

But I can see what you're getting at - what you're asking for is that 
the *container* object whose element is being assigned to is first 
queried as to whether it will accept a mutated element being assigned to 
it before that element is mutated.

This looks to be a fundamental issue with the augmented assignment 
mechanism.

E.

Thread

Re: Could you explain this rebinding (or some other action) on "nums = nums"? fl <rxjwg98@gmail.com> - 2015-11-30 18:14 -0800
  Re: Could you explain this rebinding (or some other action) on "nums = nums"? MRAB <python@mrabarnett.plus.com> - 2015-12-01 03:32 +0000
    Re: Could you explain this rebinding (or some other action) on "nums = nums"? Denis McMahon <denismfmcmahon@gmail.com> - 2015-12-01 20:32 +0000
      Re: Could you explain this rebinding (or some other action) on "nums = nums"? Ian Kelly <ian.g.kelly@gmail.com> - 2015-12-01 14:44 -0600
        Re: Could you explain this rebinding (or some other action) on "nums = nums"? Denis McMahon <denismfmcmahon@gmail.com> - 2015-12-01 21:37 +0000
          Re: Could you explain this rebinding (or some other action) on "nums = nums"? Erik <python@lucidity.plus.com> - 2015-12-01 22:34 +0000
          Re: Could you explain this rebinding (or some other action) on "nums = nums"? Erik <python@lucidity.plus.com> - 2015-12-01 22:44 +0000
      Re: Could you explain this rebinding (or some other action) on "nums = nums"? Terry Reedy <tjreedy@udel.edu> - 2015-12-01 16:18 -0500
        Re: Could you explain this rebinding (or some other action) on "nums = nums"? Denis McMahon <denismfmcmahon@gmail.com> - 2015-12-01 21:36 +0000
          Re: Could you explain this rebinding (or some other action) on "nums = nums"? Terry Reedy <tjreedy@udel.edu> - 2015-12-01 17:37 -0500

csiph-web