What to modify in the program such that ...

[buran]

This is going really into strange direction.
@jefsummers - what is the purpose of g.go property? and the class - as it is it defy the purpose of class.

to answer original question - as suggested by @ndc85430, you can use if __name__ == '__main__': block

from math import pi
 
def circle_area(r):
    return pi * (r ** 2)
 
def circle_circumference(r):
    return 2 * pi * r
 
if __name__ == "__main__":
    radius = float(input("Enter radius: "))
    print("Area =", circle_area(radius))
    print("Circumference =", circle_circumference(radius))

now, if it has to be class:

from math import pi

class Circle():
    def __init__(self, radius):
        self.radius = radius

    @property
    def area(self):
        return pi * (self.radius ** 2)
    
    @property
    def circumference(self):
        return 2 * pi * self.radius
 
if __name__ == "__main__":
    radius = float(input("Enter radius: "))
    circle = Circle(radius) # create instance of Circle class
    print("Area =", circle.area)
    print("Circumference =", circle.circumference)

in both cases nothing will happen if you import the module - functions and the class will be available to use in the other module, but the code in the if __name__ == '__main__': block will not be executed