Python 3 decimal module devision still has floating point errors-CodePudding

when using the decimal module in python, it seems that division still gives inaccurate results. Here is the code I used to check this, am I doing something wrong or is it just impossible to do division accurately with the decimal module? In that case, is there something else I could use to do this kind of calculations with accuracy?

from decimal import Decimal as D

a = D('39.37007874')
b = D('0.0254')
c = D('1')

print(c / a) #0.02540000000010160000000040640   unexpected
print(c / b) #39.37007874015748031496062992     unexpected
print(c * b) #0.0254                            expected
print(c * a) #39.37007874                       expected

CodePudding user response：

You could simply use the round function and get any number of decimals you need.

from decimal import Decimal as D

a = D('39.37007874')
b = D('0.0254')
c = D('1')

print(round(c / a, 8)) #0.02540000
print(round(c / b, 8)) #39.37007874
print(round(c * b, 8)) #0.02540000
print(round(c * a, 8)) #39.37007874

CodePudding user response：

You may want to use fractions.

from fractions import Fraction

a = Fraction('39.37007874')
b = Fraction('0.0254')
c = Fraction(1)

print(c / a)  # 50000000/1968503937
print(c / b)  # 5000/127
print(c * b)  # 127/5000
print(c * a)  # 1968503937/50000000

This will make division as accurate as possible, although other operations like sqrt() or sin() will still be as accurate as float.