[Python-bugs-list] [ python-Bugs-561913 ] float values in lists

[noreply@sourceforge.net]

Bugs item #561913, was opened at 2002-05-29 10:36
You can respond by visiting: 
http://sourceforge.net/tracker/?func=detail&atid=105470&aid=561913&group_id=5470

Category: Python Interpreter Core
Group: Python 2.2.1
Status: Closed
Resolution: Invalid
Priority: 5
Submitted By: Brian Townley (thranil)
Assigned to: Michael Hudson (mwh)
Summary: float values in lists

Initial Comment:
System: Windows 2000

Execute the following script to reproduce problem:
theList = [3.14,59,"A string", 1024] 
print theList 

What I am seeing:
The float value "3.14" is being displayed as 
3.1400000000000001. 



----------------------------------------------------------------------

>Comment By: Tim Peters (tim_one)
Date: 2002-05-29 11:06

Message:
Logged In: YES 
user_id=31435

For example, in C/C++ print with format %.17g

----------------------------------------------------------------------

Comment By: Brian Townley (thranil)
Date: 2002-05-29 10:56

Message:
Logged In: YES 
user_id=555127

The explanation given makes sense, yet I am unable to 
reproduce this floating point rounding error with a Visual C++ 
compiled project. Can you recommend a way to repro it so I 
can see this issue within a compilable language?

----------------------------------------------------------------------

Comment By: Michael Hudson (mwh)
Date: 2002-05-29 10:41

Message:
Logged In: YES 
user_id=6656

Hmm, try this URL instead:

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

(I've fixed the canned response).

----------------------------------------------------------------------

Comment By: Michael Hudson (mwh)
Date: 2002-05-29 10:39

Message:
Logged In: YES 
user_id=6656

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://python.sourceforge.net/devel-docs/tut/node14.html

----------------------------------------------------------------------

You can respond by visiting: 
http://sourceforge.net/tracker/?func=detail&atid=105470&aid=561913&group_id=5470