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Re: Serious error in int() function?

From Alain Ketterlin <alain@universite-de-strasbourg.fr.invalid>
Newsgroups comp.lang.python
Subject Re: Serious error in int() function?
Date 2016-04-13 10:00 +0200
Organization Université de Strasbourg
Message-ID <87fuuqey4s.fsf@universite-de-strasbourg.fr.invalid> (permalink)
References <52f7516c-8601-4252-ab16-bc30c59c8306@googlegroups.com>

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martin.spichty@gmail.com writes:

> print int(float(2.8/0.1))
>
> yields
>
> 27
>
> instead of 28!!

That's how floating-point arithmetic works: look at the result of
2.8/0.1 to see why int() is correct.

> Is that known?

Yes, it is known, and correct since you use "float". See
http://floating-point-gui.de/ for a nice explanation. Use decimal
(https://docs.python.org/2/library/decimal.html) if you need exact
representations.

-- Alain.

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Thread

Serious error in int() function? martin.spichty@gmail.com - 2016-04-13 00:41 -0700
  Re: Serious error in int() function? Marko Rauhamaa <marko@pacujo.net> - 2016-04-13 10:55 +0300
  Re: Serious error in int() function? Alain Ketterlin <alain@universite-de-strasbourg.fr.invalid> - 2016-04-13 10:00 +0200
  Re: Serious error in int() function? Peter Otten <__peter__@web.de> - 2016-04-13 10:03 +0200
  Re: Serious error in int() function? blindanagram@nowhere.net - 2016-04-13 09:04 +0100
  Re: Serious error in int() function? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2016-04-13 23:51 +1200
  Re: Serious error in int() function? "ast" <nomail@com.invalid> - 2016-04-14 08:52 +0200
    Re: Serious error in int() function? Christian Gollwitzer <auriocus@gmx.de> - 2016-04-14 09:25 +0200
    Accuracy of math.sqrt(), was Re: Serious error in int() function? Peter Otten <__peter__@web.de> - 2016-04-14 09:46 +0200
    Re: Serious error in int() function? blindanagram@nowhere.net - 2016-04-14 08:59 +0100
      Re: Serious error in int() function? blindanagram@nowhere.net - 2016-04-14 09:13 +0100
        Re: Serious error in int() function? blindanagram@nowhere.net - 2016-04-14 13:07 +0100
          Re: Serious error in int() function? Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2016-04-14 20:36 -0400
            Re: Serious error in int() function? Christian Gollwitzer <auriocus@gmx.de> - 2016-04-15 04:38 +0200
              Re: Serious error in int() function? John Pote <johnhpote@o2.co.uk> - 2016-04-15 12:05 +0100
                Re: Serious error in int() function? alister <alister.ware@ntlworld.com> - 2016-04-15 11:50 +0000
            Re: Serious error in int() function? blindanagram@nowhere.net - 2016-04-15 09:41 +0100
              Re: Serious error in int() function? blindanagram@nowhere.net - 2016-04-15 09:41 +0100

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