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

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On 12.07.2014 18:35, Steven D'Aprano wrote:

> If you said, "for many purposes, one should not compare floats for 
> equality, but should use some sort of fuzzy comparison instead" then I 
> would agree with you. But your insistence that equality "always" is wrong 
> takes it out of good advice into the realm of superstition.

Bullshit. Comparing floats by their representation is *generally* a bad
idea because of portability issues. You don't know if IEEE754 is used to
represent floats on the systems that your code is used on.

You're hairsplitting: when I'd have said "in 99.9% of cases" you'd agree
with me but since I said "always" you disagree. Don't lawyer out.
Comparing binary representation of floats is a crappy idea.

Even more so in the age of cloud computing where your code is executed
on who knows which architecture where the exact same high level
interpretation might lead to vastly different results. Not to mention
high performance computing, where specialized FPUs can numerously be
found which don't give a shit about IEEE754.

Another thing why it's good to NEVER compare floats with regards to
their binary representation: Do you exactly know how your FPU is
configured by your operating system. Do you know that your FPUs on a
multiprocessor system are configured all identically with regards to
754? Rounding modes, etc?

Just don't fall in the pit. Don't compare floats via equals.

>> when x < x -> False
> 
> Because not all types are ordered:
> 
> py> x = 1+3j
> py> x < x
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
> TypeError: unorderable types: complex() < complex()

Oh, so then you also don't want refelexivity of equals, I think.
Because, obviously, not all types support comparison for equality:

#!/usr/bin/python3
class Yeah(object):
	def __eq__(self, other):
		raise TypeError("Booya")
Yeah() == Yeah()

You cherrypick your logic and hairsplit in your reasoning. It's not
consistent.

Cheers,
Johannes

-- 
>> Wo hattest Du das Beben nochmal GENAU vorhergesagt?
> Zumindest nicht öffentlich!
Ah, der neueste und bis heute genialste Streich unsere großen
Kosmologen: Die Geheim-Vorhersage.
 - Karl Kaos über Rüdiger Thomas in dsa <hidbv3$om2$1@speranza.aioe.org>

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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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