Precise Multiplication without floating point arithmetic

Question

How can I get the exact result of a multiplication?

Python tells me that 0.017 * 3 equals 0.051000000000000004. Is there any command to make python print 0.051?

Answer 1

Fractional numeric literals in Python have the type float, which is represented in binary. Use the Decimal type for base 10 arithmetic.

>>> from decimal import Decimal
>>> print(Decimal('0.017') * 3)
0.051

Answer 2

Assuming you know the expected number of significant digits the operation should output, you can use the built-in rounding function in python (in this case 3).

>>> round(0.017 * 3, 3)
0.051