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

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On Sun, Jul 13, 2014 at 2:35 AM, Steven D'Aprano
<steve+comp.lang.python@pearwood.info> wrote:
> You're not going to hear me arguing that the non-reflexivity of NANs and
> SQL NULL is a bad idea, although some very smart people have:
>
> http://bertrandmeyer.com/2010/02/06/reflexivity-and-other-pillars-of-civilization/
>
> Mathematical equality is reflexive. It is fundamental to the nature of
> numbers and equality that a number is always equal to itself. To the
> degree that floats are supposed to model real numbers, they should obey
> the same laws of real numbers. However, they already fail to obey them,
> so the failure of reflexivity is just one more problem that makes
> floating point such a hard problem. Compared to floating point
> arithmetic, calculus is easy.
>

And there are plenty of other laws of real numbers that floats violate
(or, let's be generous, "approximate to rather than following
perfectly"). For instance, adding two positive (non-zero) numbers
should result in a number which is greater than either, but thanks to
rounding, that's not always true. (Not to mention that "infinity"
isn't a number, but it is a floating-point value.) The problem is not
equality comparisons, the problem is the expectation that the rules of
reals apply to floats.

ChrisA

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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

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