[ python-Bugs-1222098 ] float() not accurate

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Bugs item #1222098, was opened at 2005-06-16 18:00
Message generated for change (Comment added) made by nascheme
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Category: Type/class unification
Group: Python 2.4
>Status: Closed
>Resolution: Invalid
Priority: 5
Submitted By: Brian Dols (dols)
Assigned to: Nobody/Anonymous (nobody)
Summary: float() not accurate

Initial Comment:

float("4.1") returns 4.0999999999996

shouldn't it return 4.1?


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Comment By: Neil Schemenauer (nascheme)
Date: 2005-06-16 18:27

Message:
Logged In: YES 
user_id=35752

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 more information:

http://www.python.org/doc/2.2.1/tut/node14.html

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