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

Groups > comp.lang.python > #74248

Re: Proposal: === and !=== operators

Path csiph.com!usenet.pasdenom.info!weretis.net!feeder4.news.weretis.net!rt.uk.eu.org!newsfeed.xs4all.nl!newsfeed3a.news.xs4all.nl!xs4all!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail
Return-Path <jeanpierreda@gmail.com>
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; 'python,': 0.02; 'operator': 0.03; 'cache': 0.07; 'pypy': 0.07; 'immutable': 0.09; 'integers': 0.09; 'meaningful': 0.09; 'raises': 0.09; 'things,': 0.09; 'cc:addr:python-list': 0.11; 'python': 0.11; 'suggest': 0.14; '"is': 0.16; '"is"': 0.16; '__ne__': 0.16; 'backwards': 0.16; 'behave': 0.16; 'fuzzy': 0.16; 'nan': 0.16; 'objects.': 0.16; 'operators,': 0.16; 'sorts': 0.16; 'subject:operators': 0.16; 'to:addr:pearwood.info': 0.16; "to:name:steven d'aprano": 0.16; '(you': 0.16; 'wrote:': 0.18; 'wed,': 0.18; 'cc:addr:python.org': 0.22; '(or': 0.24; 'cc:2**0': 0.24; 'equivalent': 0.26; 'second': 0.26; 'header:In-Reply-To:1': 0.27; 'am,': 0.29; "doesn't": 0.30; 'message-id:@mail.gmail.com': 0.30; 'url:wiki': 0.31; 'breaking': 0.31; "d'aprano": 0.31; 'steven': 0.31; 'covered': 0.32; '(e.g.': 0.33; "i'd": 0.34; 'classes': 0.35; 'objects': 0.35; 'but': 0.35; 'received:google.com': 0.35; 'false': 0.36; 'similar': 0.36; 'url:org': 0.36; 'should': 0.36; 'behind': 0.37; 'two': 0.37; 'problems': 0.38; 'expect': 0.39; 'even': 0.60; 'most': 0.60; 'matter': 0.61; 'first': 0.61; 'guarantee': 0.63; 'skip:n 10': 0.64; 'choose': 0.64; 'different': 0.65; 'great': 0.65; '(that': 0.65; 'anything.': 0.68; 'jul': 0.74; 'much,': 0.84; 'scenes': 0.84; 'url:php': 0.85; 'same,': 0.91; 'subject:Proposal': 0.91
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 :cc:content-type; bh=lwIMftIuEtkxrv00pcaifdH2iMXMhJVRp7Y7QbPWG5o=; b=LVLyGcf50TCJ/fdITJzIcpgwpe3ptRIFcYZLNtZbw7tGuMZIq1tJ0OUVtD+A8L79dt pxO3kEZYHGxHlI1cRdSlBqMn566ZgN4J+IVCl65zHnxoGvQT0U+NKmALn3TmTjd78NbT YF5V9r5rBtBYj1N3+k2JNVgXJ+tVIM4lV4i/OpJX/FOgF5wuo37m8WmFBVVeDE9hwENf VEhjPwz1YozeQ5xHYhEMkEs4uo3tqozYpvzlyIVnV71ZEG/zwMe7Nt5vjo69JVTDK8uN Ihozr3n7FFGZ1Uo60xCoGgUDlyEM8JrTEMZJ6bo2ULmklge1o7MwQPhqURkthXi0J8u0 gyfw==
X-Received by 10.224.112.131 with SMTP id w3mr72666206qap.68.1404907341747; Wed, 09 Jul 2014 05:02:21 -0700 (PDT)
MIME-Version 1.0
In-Reply-To <53bce8a3$0$2746$c3e8da3$76491128@news.astraweb.com>
References <53bce8a3$0$2746$c3e8da3$76491128@news.astraweb.com>
From Devin Jeanpierre <jeanpierreda@gmail.com>
Date Wed, 9 Jul 2014 05:01:41 -0700
Subject Re: Proposal: === and !=== operators
To "Steven D'Aprano" <steve@pearwood.info>
Content-Type text/plain; charset=UTF-8
Cc "comp.lang.python" <python-list@python.org>
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.11687.1404907345.18130.python-list@python.org> (permalink)
Lines 32
NNTP-Posting-Host 2001:888:2000:d::a6
X-Trace 1404907345 news.xs4all.nl 2876 [2001:888:2000:d::a6]:40375
X-Complaints-To abuse@xs4all.nl
Xref csiph.com comp.lang.python:74248

Show key headers only | View raw

On Wed, Jul 9, 2014 at 12:00 AM, Steven D'Aprano <steve@pearwood.info> wrote:
> At the moment, Python has two (in)equality operators, == and != which
> call __eq__ and __ne__ methods. Some problems with those:
>
>
> * Many people expect == to always be reflexive (that is, x == x for
>   every x) but classes which customise __eq__ may not be.
>
> * The == operator requires __eq__ to return True or False
>   (or NotImplemented) and raises TypeError if it doesn't, which
>   makes it impossible to use == with (say) three-valued or fuzzy
>   logic.

Counter-proposal: The second use case doesn't matter that much, and
can be added to == without breaking backwards compatibility
meaningfully. The first case is covered by all sorts of things, but
I'd suggest that the most meaningful way in which nan "is the same as"
nan is that they both behave the same, as objects.

The Python "is" operator returns True when two objects are identical.
Is it a great leap to guarantee, in Python, that equivalent immutable
objects are always identical? Then float('nan') is float('nan') should
always return True. We already implicitly allow that a Python
implementation may choose to do this (e.g. small integers are cached),
but it isn't so hard to guarantee it. (You don't even have to cache
anything. PyPy makes things is-identical even when they are behind the
scenes different objects in memory, IIRC.)

See also http://wiki.ecmascript.org/doku.php?id=harmony:egal , which
is a similar proposal for ES6.

-- Devin

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

Thread

Proposal: === and !=== operators Steven D'Aprano <steve@pearwood.info> - 2014-07-09 07:00 +0000
  Re: Proposal: === and !=== operators Chris Angelico <rosuav@gmail.com> - 2014-07-09 17:21 +1000
    Re: Proposal: === and !=== operators Steven D'Aprano <steve@pearwood.info> - 2014-07-09 09:17 +0000
      Re: Proposal: === and !=== operators Rustom Mody <rustompmody@gmail.com> - 2014-07-09 09:20 -0700
      Re: Proposal: === and !=== operators Ian Kelly <ian.g.kelly@gmail.com> - 2014-07-09 11:50 -0600
      Re: Proposal: === and !=== operators Cameron Simpson <cs@zip.com.au> - 2014-07-10 09:16 +1000
      Re: Proposal: === and !=== operators Johannes Bauer <dfnsonfsduifb@gmx.de> - 2014-07-12 13:54 +0200
        Re: Proposal: === and !=== operators Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-07-12 16:35 +0000
          Re: Proposal: === and !=== operators Chris Angelico <rosuav@gmail.com> - 2014-07-13 02:54 +1000
            Re: Proposal: === and !=== operators Roy Smith <roy@panix.com> - 2014-07-12 16:39 -0400
          Re: Proposal: === and !=== operators Johannes Bauer <dfnsonfsduifb@gmx.de> - 2014-07-12 20:14 +0200
            Re: Proposal: === and !=== operators Chris Angelico <rosuav@gmail.com> - 2014-07-13 09:01 +1000
              Re: Proposal: === and !=== operators Roy Smith <roy@panix.com> - 2014-07-12 19:06 -0400
                Re: Proposal: === and !=== operators Chris Angelico <rosuav@gmail.com> - 2014-07-13 09:15 +1000
            Re: Proposal: === and !=== operators Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-07-13 04:48 +0000
  Re: Proposal: === and !=== operators Cameron Simpson <cs@zip.com.au> - 2014-07-09 18:17 +1000
    Re: Proposal: === and !=== operators Steven D'Aprano <steve@pearwood.info> - 2014-07-09 09:02 +0000
      Re: Proposal: === and !=== operators Chris Angelico <rosuav@gmail.com> - 2014-07-09 19:23 +1000
  Re: Proposal: === and !=== operators Devin Jeanpierre <jeanpierreda@gmail.com> - 2014-07-09 05:01 -0700
  Re: Proposal: === and !=== operators Roy Smith <roy@panix.com> - 2014-07-09 08:27 -0400
    Re: Proposal: === and !=== operators Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-07-09 12:48 +0000
      Re: Proposal: === and !=== operators Tim Chase <python.list@tim.thechases.com> - 2014-07-09 13:05 -0500
        Re: Proposal: === and !=== operators Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-07-10 01:10 +0000
      Re: Proposal: === and !=== operators Ian Kelly <ian.g.kelly@gmail.com> - 2014-07-09 12:31 -0600
      Re: Proposal: === and !=== operators Roy Smith <roy@panix.com> - 2014-07-09 16:47 -0400
  Re: Proposal: === and !=== operators Ethan Furman <ethan@stoneleaf.us> - 2014-07-09 05:43 -0700
  Re: Proposal: === and !=== operators Robert Kern <robert.kern@gmail.com> - 2014-07-09 16:27 +0100
  Re: Proposal: === and !=== operators Alex Burke <alexjeffburke@gmail.com> - 2014-07-10 18:33 +0200
  Re: Proposal: === and !=== operators Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-07-12 03:30 +0000
    Re: Proposal: === and !=== operators Alan Bawden <alan@scooby-doo.csail.mit.edu> - 2014-07-12 01:07 -0400
      Re: Proposal: === and !=== operators Torsten Bronger <bronger@physik.rwth-aachen.de> - 2014-07-12 08:05 +0200
        Re: Proposal: === and !=== operators Torsten Bronger <bronger@physik.rwth-aachen.de> - 2014-07-12 08:14 +0200
      Re: Proposal: === and !=== operators Chris Angelico <rosuav@gmail.com> - 2014-07-12 16:06 +1000
      Re: Proposal: === and !=== operators Ethan Furman <ethan@stoneleaf.us> - 2014-07-11 23:11 -0700
      Re: Proposal: === and !=== operators Chris Angelico <rosuav@gmail.com> - 2014-07-12 16:39 +1000
        Re: Proposal: === and !=== operators Marko Rauhamaa <marko@pacujo.net> - 2014-07-12 10:06 +0300
      Re: Proposal: === and !=== operators Ethan Furman <ethan@stoneleaf.us> - 2014-07-11 23:53 -0700
      Re: Proposal: === and !=== operators Chris Angelico <rosuav@gmail.com> - 2014-07-12 17:25 +1000
      Re: Proposal: === and !=== operators Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-07-12 08:33 +0000

csiph-web