Alexander Belopolsky added the comment:

On Sep 19, 2012, at 5:36 PM, Ram Rachum <rep...@bugs.python.org> wrote:

> Why would we use float to represent the ratio of the bonus to the client?

Because float is the builtin type that Python provides to represent such 
quantities. 

> Why would we risk imprecision there when Decimal provides us with perfect 
> precision?

Python float is a much simpler and more efficient type than Decimal.  One 
should have a really good reason to introduce Decimal in the program.  In case 
of money, Decimal provides a *lower* precision alternative to float together 
with the control over rounding direction.  This is important in applications 
where fractions of a penny have to be dealt with in very precise manner. 

In your application, float is a perfectly good type to represent 15% bonus.  
Even if your customers insist on microsecond precision, float is good enough 
and timedelta resolution will prevent you from supporting higher precision 
anyways. 

As I mentioned before, I would be happy to see greater interoperability between 
numerical types in Python and interoperability between timedelta and Decimal 
may come as a side benefit of that effort.  However, I don't find your use case 
to be compelling enough to either justify special case code or to motivate a 
more general effort.

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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue14262>
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