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

Groups > comp.lang.python > #86981

Re: Is nan in (nan,) correct?

Return-Path <rosuav@gmail.com>
X-Original-To python-list@python.org
Delivered-To python-list@mail.python.org
X-Spam-Status OK 0.006
X-Spam-Evidence '*H*': 0.99; '*S*': 0.00; 'operator': 0.03; 'interpreter': 0.05; 'url:pipermail': 0.05; 'assuming': 0.09; 'correct,': 0.09; 'topic:': 0.09; 'cc:addr:python-list': 0.11; 'python': 0.11; 'discusses': 0.16; 'finney': 0.16; 'from:addr:rosuav': 0.16; 'from:name:chris angelico': 0.16; 'implies': 0.16; 'nick': 0.16; 'python-dev,': 0.16; 'wrote:': 0.18; 'cc:addr:python.org': 0.22; 'cc:2**0': 0.24; 'compare': 0.26; 'specially': 0.26; 'post': 0.26; 'header:In-Reply-To:1': 0.27; 'point': 0.28; 'correct': 0.29; 'message- id:@mail.gmail.com': 0.30; "i'm": 0.30; 'steven': 0.31; 'url:python': 0.33; 'fri,': 0.33; 'problem': 0.35; 'subject: (': 0.35; 'received:google.com': 0.35; 'subject:?': 0.36; 'url:org': 0.36; 'example,': 0.37; 'being': 0.38; 'ben': 0.38; 'needed': 0.38; 'issue': 0.38; 'pm,': 0.38; 'sure': 0.39; 'url:mail': 0.40; 'is.': 0.60; 'skip:\xe2 10': 0.65; 'mar': 0.68; '8bit%:43': 0.74; '2015': 0.84; 'optimisation': 0.84; 'url:python-dev': 0.84; 'to:none': 0.92
DKIM-Signature v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:cc :content-type:content-transfer-encoding; bh=SGgMhp3Msm3TAPNgy9uWcqR8cDdRwkyReic9O2P98x8=; b=uARFuwjvkoFFgsd1GbNrbVcsJb8V0ds6/WlNqrEfKpflkxXLcg6CVW3xrrtW8WnH96 Z8PdNUf/Mpczuer/CnweHybD3Y/jT0KpHTdaJwACl9rgmNdVC616UkOO0PaGGJAF8jdm nmUHRlCxFgytOrccvpIsz300B70V0YSJB0POXxfuYz4YfevGL3mKqtbOVglSTLcW24JF MJX3AhToAYBFz+umlLw8K4tKyhajWwvji+/wywluoKDTgSwt6424nTRCDSTaO9C3o6dc 7tsUUfdgAudp/U98orHG+L8X+Z9kKUUrfPqVHPiOZxf+bg8sxz3O8IxMoTFdOp+9cxre 7v6A==
MIME-Version 1.0
X-Received by 10.42.203.147 with SMTP id fi19mr7827697icb.12.1425613742469; Thu, 05 Mar 2015 19:49:02 -0800 (PST)
In-Reply-To <85wq2uyffs.fsf@benfinney.id.au>
References <mailman.67.1425594415.21433.python-list@python.org> <54f90c53$0$12994$c3e8da3$5496439d@news.astraweb.com> <858ufazvff.fsf@benfinney.id.au> <54F91C70.6020303@stoneleaf.us> <85wq2uyffs.fsf@benfinney.id.au>
Date Fri, 6 Mar 2015 14:49:02 +1100
Subject Re: Is nan in (nan,) correct?
From Chris Angelico <rosuav@gmail.com>
Cc "python-list@python.org" <python-list@python.org>
Content-Type text/plain; charset=UTF-8
Content-Transfer-Encoding quoted-printable
X-BeenThere python-list@python.org
X-Mailman-Version 2.1.19
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.83.1425613750.21433.python-list@python.org> (permalink)
Lines 21
NNTP-Posting-Host 2001:888:2000:d::a6
X-Trace 1425613750 news.xs4all.nl 2947 [2001:888:2000:d::a6]:58890
X-Complaints-To abuse@xs4all.nl
Path csiph.com!usenet.pasdenom.info!bete-des-vosges.org!feed.ac-versailles.fr!nerim.net!novso.com!newsfeed.xs4all.nl!newsfeed3a.news.xs4all.nl!xs4all!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail
Xref csiph.com comp.lang.python:86981

Show key headers only | View raw

On Fri, Mar 6, 2015 at 2:26 PM, Ben Finney <ben+python@benfinney.id.au> wrote:
> Isn't the point at issue that the Python interpreter *may* optimise by
> assuming ‘is implies equality’, so the ‘in’ operator can fail if that
> assumption is false?
>
> I thought the problem was that types with custom behaviour, as with the
> ‘NullType’ example, needed to deal specially with the ‘is implies
> equality’ optimisation Steven explained.
>
> If that's the correct behaviour, and we can *depend* on it being
> correct, then I don't see what the problem is.

I'm not sure it's just an optimization. Compare this post from
python-dev, where Nick Coghlan discusses the same topic:

https://mail.python.org/pipermail/python-dev/2014-July/135476.html

ChrisA

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

Thread

Is nan in (nan,) correct? random832@fastmail.us - 2015-03-05 17:26 -0500
  Re: Is nan in (nan,) correct? sohcahtoa82@gmail.com - 2015-03-05 15:11 -0800
    Re: Is nan in (nan,) correct? Ben Finney <ben+python@benfinney.id.au> - 2015-03-06 10:20 +1100
      Re: Is nan in (nan,) correct? sohcahtoa82@gmail.com - 2015-03-05 15:27 -0800
        Re: Is nan in (nan,) correct? Ben Finney <ben+python@benfinney.id.au> - 2015-03-06 10:39 +1100
        Re: Is nan in (nan,) correct? Chris Angelico <rosuav@gmail.com> - 2015-03-06 10:40 +1100
    Re: Is nan in (nan,) correct? Chris Angelico <rosuav@gmail.com> - 2015-03-06 10:25 +1100
  Re: Is nan in (nan,) correct? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-03-06 13:09 +1100
    Re: Is nan in (nan,) correct? Ben Finney <ben+python@benfinney.id.au> - 2015-03-06 13:55 +1100
    Re: Is nan in (nan,) correct? Ethan Furman <ethan@stoneleaf.us> - 2015-03-05 19:18 -0800
    Re: Is nan in (nan,) correct? Ben Finney <ben+python@benfinney.id.au> - 2015-03-06 14:26 +1100
    Re: Is nan in (nan,) correct? Ethan Furman <ethan@stoneleaf.us> - 2015-03-05 19:44 -0800
    Re: Is nan in (nan,) correct? Chris Angelico <rosuav@gmail.com> - 2015-03-06 14:49 +1100
    Re: Is nan in (nan,) correct? random832@fastmail.us - 2015-03-05 23:37 -0500
      Re: Is nan in (nan,) correct? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-03-07 04:07 +1100
    Re: Is nan in (nan,) correct? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-03-06 04:46 +0000
  Re: Is nan in (nan,) correct? Rustom Mody <rustompmody@gmail.com> - 2015-03-06 01:50 -0800
    Re: Is nan in (nan,) correct? Chris Angelico <rosuav@gmail.com> - 2015-03-06 21:01 +1100
      Re: Is nan in (nan,) correct? Rustom Mody <rustompmody@gmail.com> - 2015-03-06 02:22 -0800
        Re: Is nan in (nan,) correct? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-03-07 03:59 +1100
          Re: Is nan in (nan,) correct? Rustom Mody <rustompmody@gmail.com> - 2015-03-06 10:04 -0800
            Re: Is nan in (nan,) correct? Ethan Furman <ethan@stoneleaf.us> - 2015-03-06 10:16 -0800
      Re: Is nan in (nan,) correct? Grant Edwards <invalid@invalid.invalid> - 2015-03-06 15:34 +0000
    Re: Is nan in (nan,) correct? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-03-07 03:43 +1100
      Re: Is nan in (nan,) correct? Rustom Mody <rustompmody@gmail.com> - 2015-03-06 09:04 -0800
        Re: Is nan in (nan,) correct? Chris Angelico <rosuav@gmail.com> - 2015-03-07 04:16 +1100
          Re: Is nan in (nan,) correct? Rustom Mody <rustompmody@gmail.com> - 2015-03-06 09:36 -0800
        Re: Is nan in (nan,) correct? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-03-07 10:33 +1100
          Re: Is nan in (nan,) correct? Rustom Mody <rustompmody@gmail.com> - 2015-03-06 18:37 -0800

csiph-web