off topic but please forgive me me and answer

Steven D'Aprano steve at REMOVE-THIS-cybersource.com.au
Sat Apr 3 01:07:53 CEST 2010


On Fri, 02 Apr 2010 12:35:55 -0700, Mensanator wrote:

>> If you want an exact result when multiplying arbitrary fractions, you
>> need to avoid floats and decimals and use Fractions:
>>
>> >>> Fraction(1, 2)**2
>>
>> Fraction(1, 4)
> 
> Where do you get that from?

Where do I get what from? Fraction? Oops, sorry about that.

In Python2.6:

>>> from fractions import Fraction

In older Pythons, there was a demo module Demo/classes/Rat.py but it may 
not be installed on your system. See http://bugs.python.org/issue1682

If you meant, where did I get the statement about exact results from, 
both float and Decimal are fixed precision numbers. float precision is 
fixed by the operating system and/or hardware; Decimal precision can be 
arbitrarily chosen by the caller, but having made that choice, 
calculations are rounded to that precision. Only Fraction gives exact 
results for any arbitrary rational number.



-- 
Steven



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