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Fri Apr 20 07:41:18 EDT 2001 · http://mail.python.org/pipermail/python-list/2001-April/086712.html

At 12:48 20/04/01 +0200, M.-A. Lemburg wrote:
>Well, Moshe's plan is to have 1.123 result in a Rational(1123, 1000)
>being created (instead of a Python float). The extension should
>make playing with this idea a whole lot easier.

The problem is that, as of now, you have no way to know if the user 
supplied you with

   Rational(1.123)

or

   Rational(1.122999999999...)  # as many 9's as your platform supports

So I think that creating rationals must use either the Rational(a/b) form, 
or the Rational(string) form. Please bear in mind that, for Moshe's plan to 
work, it would be needed to convert the number to the rational format at 
the parser level, when it is still represented as a string.

Using a float to make rational value does not make sense given all problems 
of the float representation. The result can't be trusted, except if you 
supply both the float and the number of decimal digits you are working with 
(example: Rational(1.123, digits=3). This way the conversion routine can 
round up the number before trying to convert it to the rational format.

Carlos Ribeiro

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Showing content from http://mail.python.org/pipermail/python-list/2001-April/086712.html below:

ANN: Experimental Number Types (Integer, Rational, Floats)