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Re: python 3.44 float addition bug?

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Date Fri, 20 Jun 2014 18:07:58 -0700
From Gary Herron <gary.herron@islandtraining.com>
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On 06/20/2014 05:57 PM, FraserL wrote:
> I think I found a strange bug in python 3.4.1,


No, this is not a bug in Python.  There is a limitation of floating 
point arithmetic in *all* languages, on *all* computers.   Python 3 may 
be the first to let you see this limitation, but it's always been there.

See https://docs.python.org/2/tutorial/floatingpoint.html for more details.

Gary Herron



>
> fresh install of
>
>   https://www.python.org/ftp/python/3.4.1/python-3.4.1.amd64.msi
>
> and a fresh install of
> https://www.python.org/ftp/python/2.7.7/python-2.7.7.amd64.msi
> to compare it to.
>
> #test code
> z = 0.01
> p = 0.0
> for x, y in enumerate(range(1, 20)):
>      p += z
>      print(p)
> #end
>
>
> 3.4.1 output:
>
> 0.01
> 0.02
> 0.03
> 0.04
> 0.05
> 0.060000000000000005
> 0.07
> 0.08
> 0.09
> 0.09999999999999999
> 0.10999999999999999
> 0.11999999999999998
> 0.12999999999999998
> 0.13999999999999999
> 0.15
> 0.16
> 0.17
> 0.18000000000000002
> 0.19000000000000003
>
>
> 2.7.7 output:
>
> 0.01
> 0.02
> 0.03
> 0.04
> 0.05
> 0.06
> 0.07
> 0.08
> 0.09
> 0.1
> 0.11
> 0.12
> 0.13
> 0.14
> 0.15
> 0.16
> 0.17
> 0.18
> 0.19
>
>
> I'm not hugely accustomed to Python, but this seems crazy to me.

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Thread

python 3.44 float addition bug? FraserL <fraser.long+usenet@NOSPAMgmail.com> - 2014-06-20 19:57 -0500
  Re: python 3.44 float addition bug? FraserL <fraser.long+usenet@gmail.com> - 2014-06-20 20:11 -0500
    Re: python 3.44 float addition bug? Gary Herron <gary.herron@islandtraining.com> - 2014-06-20 18:19 -0700
  Re: python 3.44 float addition bug? Gary Herron <gary.herron@islandtraining.com> - 2014-06-20 18:07 -0700
  Re: python 3.44 float addition bug? Chris Angelico <rosuav@gmail.com> - 2014-06-21 11:33 +1000
  Re: python 3.44 float addition bug? INADA Naoki <songofacandy@gmail.com> - 2014-06-21 10:06 +0900
  Re: python 3.44 float addition bug? Grant Edwards <invalid@invalid.invalid> - 2014-06-21 14:25 +0000
  Re: python 3.44 float addition bug? Ned Deily <nad@acm.org> - 2014-06-21 12:24 -0700
    Re: python 3.44 float addition bug? buck <workitharder@gmail.com> - 2014-06-23 17:55 -0700
      Re: python 3.44 float addition bug? Chris Angelico <rosuav@gmail.com> - 2014-06-24 13:26 +1000
      Re: python 3.44 float addition bug? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-06-24 17:30 +1200
      Re: python 3.44 float addition bug? Steven D'Aprano <steve@pearwood.info> - 2014-06-24 06:34 +0000
  Re: python 3.44 float addition bug? Maciej Dziardziel <fiedzia@gmail.com> - 2014-06-25 14:12 -0700
    Re: python 3.44 float addition bug? Steven D'Aprano <steve@pearwood.info> - 2014-06-26 02:56 +0000
      Re: python 3.44 float addition bug? Chris Angelico <rosuav@gmail.com> - 2014-06-26 13:13 +1000
        Re: python 3.44 float addition bug? Steven D'Aprano <steve@pearwood.info> - 2014-06-26 04:17 +0000
          Re: python 3.44 float addition bug? Chris Angelico <rosuav@gmail.com> - 2014-06-26 14:41 +1000
      Re: python 3.44 float addition bug? Ben Finney <ben@benfinney.id.au> - 2014-06-26 13:39 +1000
        Re: python 3.44 float addition bug? Steven D'Aprano <steve@pearwood.info> - 2014-06-26 09:15 +0000
          Re: python 3.44 float addition bug? Chris Angelico <rosuav@gmail.com> - 2014-06-26 19:38 +1000
            Re: python 3.44 float addition bug? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-06-27 02:51 +0000
              Re: python 3.44 float addition bug? Chris Angelico <rosuav@gmail.com> - 2014-06-27 13:24 +1000
              Re: python 3.44 float addition bug? Ian Kelly <ian.g.kelly@gmail.com> - 2014-06-27 10:18 -0600
      Re: python 3.44 float addition bug? Stefan Behnel <stefan_ml@behnel.de> - 2014-06-26 07:53 +0200

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