143 – Decimals

Fractions are very useful but sometimes it is not very helpful to compute 1 / 7 and get 1/7 as a result…

Instead, you may want to use the module decimal and its class decimal.Decimal to compute fast, correctly-rounded floating-point arithmetic:

from decimal import Decimal

print(1.1 + 2.2)  # 3.3000000000000003

d = Decimal("1.1") + Decimal("2.2")
print(d)  # 3.3
print(repr(d))  # Decimal('3.3')

One good thing about the module decimal is that you can set the precision (number of decimal places) with which results are computed:

from decimal import getcontext

getcontext().prec = 6
print(Decimal(1) / Decimal(7))  # 0.142857

getcontext().prec = 28
print(Decimal(1) / Decimal(7))  # 0.1428571428571428571428571429