Quick Summary

Use the math.pi constant

import math


math is a module from the Python Standard Library, which means that you'll have it available with any Python version, without installing any additional packages.

numpy.pi constant

If you're already using Numpy, it conveniently provides π as a constant.

import numpy as np


scipy.py constant

Similar to numpy, scipy also comes with a predefined pi constant

import scipy


Are they all the same?

If you're wondering which constant to use, they are all the same value. You can check this for yourself:

import math
import numpy
import scipy

print(math.pi == numpy.pi)
> True
print(math.pi == scipy.pi)
> True

If you're not using the libraries for scientific and numerical computing, numpy / scipy , your best bet is  math.pi from the standard library.

Otherwise, it just depends on the circumstance. Typically you'll want to minimize the number of module imports and be consistent with the rest of the codebase, so that may help you decide.