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NNTP-Posting-Date: Wed, 13 Apr 2016 03:04:24 -0500
Subject: Re: Serious error in int() function?
To: martin.spichty@gmail.com
References: <52f7516c-8601-4252-ab16-bc30c59c8306@googlegroups.com>
Newsgroups: comp.lang.python
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Date: Wed, 13 Apr 2016 09:04:25 +0100
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On 13/04/2016 08:41, martin.spichty@gmail.com wrote:
> Hi,
> 
> there may be a serious error in python's int() function:
> 
> print int(float(2.8/0.1))
> 
> yields
> 
> 27
> 
> instead of 28!!
> 
> I am using Python Python 2.7.6, GCC 4.8.2 on Linux Ubuntu.
> 
> Is that known?

This arises because finite floating point arithmetic is not exact so
2.8/0.1 results in 27.999999999999996.  And, since the int() function
truncates towards zero, this results in a value of 27.

If you want the nearest integer you should use round(x) rather than int(x).