comparing fractional parts of floats

[casevh]

Starting with an example that fails the "multiply by 10" approach:

>>> math.modf(22.7)[0]*10
6.999999999999993

You can use the fractions module:

Note: the following fails when the denominator is either 1, 2 or 5.

>>> from fractions import Fraction
>>> Fraction(22.7)
Fraction(6389481971331891, 281474976710656)
>>> Fraction(22.7).limit_denominator(10)
Fraction(227, 10)
>>> a=Fraction(22.7).limit_denominator(10)
>>> divmod(a.numerator, a.denominator)
(22, 7)

The following version should handle the cases when the denominator is not 10. It also uses the output of modf directly.

>>> a=Fraction(math.modf(22.7)[0]).limit_denominator(10)
>>> divmod(10,a.denominator)[0]*a.numerator
7