[Python-bugs-list] [ python-Bugs-426711 ] Floating Point Curiosity in Python 2.1

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Bugs item #426711, was updated on 2001-05-23 11:27
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Category: None
>Group: Not a Bug
>Status: Closed
>Resolution: Invalid
Priority: 5
Submitted By: Daniel Graham (danielgraham)
Assigned to: Nobody/Anonymous (nobody)
Summary: Floating Point Curiosity in Python 2.1

Initial Comment:
[GCC 2.96 20000731 (Red Hat Linux 7.1 2.96-81)] on
linux 2

In python 2.1	in python 1.5.2
>>> .10*103
10.300000000000001	10.3	
>>>round(.10*103,2)
10.300000000000001	10.3
>>>round(.10*103.123,1)
10.300000000000001	10.3
>>>round(.10*103.123,2)
10.31			10.31
>>>round(.0*103.123,3)
10.311999999999999	10.312


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Comment By: Tim Peters (tim_one)
Date: 2001-05-23 11:33

Message:
Logged In: YES 
user_id=31435

This is not a bug.

Binary floating point cannot represent decimal fractions exactly,
so some rounding always occurs (even in Python 1.5.2).

What changed is that Python 2.0 shows more precision than before
in certain circumstances (repr() and the interactive prompt). 

You can use str() or print to get the old, rounded output: 

>>> print 0.1+0.1
0.2
>>>

Follow the link for a detailed example:

http://www.python.org/cgi-bin/moinmoin/RepresentationError


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