Using `mock.patch` to redefine sin & cos

circle.py

from math import cos, sin, pi

def point_on_circle(theta):
    return (cos(theta), sin(theta))

run1.py

#!/usr/bin/env python

import numpy as np

from circle import point_on_circle

pt = point_on_circle(np.pi/4)
print(pt)

# output is: (0.7071067811865476, 0.7071067811865475)

run2.py

#!/usr/bin/env python

import contextlib
import mock

import numpy as np

from circle import point_on_circle


def str_cos(theta):
    return "cos({})".format(theta)

def str_sin(theta):
    return "sin({})".format(theta)

with contextlib.nested(
        mock.patch('circle.cos', str_cos),
        mock.patch('circle.sin', str_sin)):
    pt = point_on_circle(np.pi/4)
    print(pt)
    
# output is now: ('cos(0.785398163397)', 'sin(0.785398163397)')