Native Python float values use your computer hardware directly, so any value is represented internally as a binary fraction. That means that you usually work with approximations, not exact values: In : format(0.1, '.17f') Out: '0.10000000000000001' The decimal module lets you use decimal floating point arithmetic with arbitrary precision: In : Decimal(1) / Decimal(3) Out: Decimal('0.3333333333333333333333333333') That's still can be not enough: In [61]: Decimal(1) / Decimal(3) * Decimal(3) == Decimal(1) Out[61]: False For perfect computations, you can use fractions, that stores any number as a rational one: In : Fraction(1) / Fraction(3) * Fraction(3) == Fraction(1) Out: True The obvious limitation is you still have to use approximations to irrational numbers (such as π).