Use more decimals in Python

Question

I already have a code which uses the bisection method to determine the value of something, the problem is that I need a value so precise, more than 15 decimals, and at some

Answer 1

You are asking if you can change the Python builtin type of floating point literals from float to (for example) decimal.Decimal. You can't do that.

Other things to consider

If decimal.Decimal is central to your code, you could import it with a shorter name:

from decimal import Decimal as Dec
x1 = Dec('0.234')
y1 = Dec('4.32')
x2 = Dec('4.321')
y2 = Dec('5.87')

Type annotations can help you to not miss conversions:

def distance(x1: Dec, y1: Dec, x2: Dec, y2: Dec) -> Dec:
    return Dec.sqrt((x2 - x1)**2 + (y2 - y1)**2)

If precision is important, initialize decimal.Decimal with a string instead of float. Floats can't exactly represent simple numbers, like for example 0.2:

>>> Dec(0.2)
Decimal('0.200000000000000011102230246251565404236316680908203125')
>>> Dec('0.2')
Decimal('0.2')

There is probably a limited number of places where you have to convert to Decimal. Most operations on Decimal either gives a new Decimal, or throws an exception.

>>> d = distance(x1, y1, x2, y2)
>>> d
Decimal('4.371048958774083555277441787')
>>> (d + x1*x2 + y1*y2**2) / 100
Decimal('1.542359709587740835552774418')

I know this is not perfect, but it might help.