Convert a float to a Decimal object in Python

We can convert a float to a Decimal object in Python like this.

from decimal import Decimal

d1 = Decimal(-7.8)
d2 = Decimal('-7.8')

print(d1)  # -7.79999999999999982236431605997495353221893310546875
print(d2)  # -7.8

print(type(d1))  # <class 'decimal.Decimal'>

a1 = d1 / 3
a2 = d2 / 3

print(a1)  # -2.599999999999999940788105353
print(a2)  # -2.6

print(type(a1))  # <class 'decimal.Decimal'>

The Decimal object is declared with a float or string value. As showed in the above example, the Decimal whose argument is a float is not exactly represented as -7.8 but d2, taking a string argument, is exactly represented.

The Decimal supports the exact calculation like $7.8 \div 3 = 2.6$.