Python | Implement Interface using class

Program:

import math

#Interface
class Shape:
    def input(self):
        pass
    def process(self):
        pass
    def output(self):
        pass

class Circle(Shape):
    def __init__(self,rad=0.0):
        self.__radius=rad
        self.__area = 0.0
    def input(self):
        self.__radius=float(input("Enter radius:"))
    def process(self):
        self.__area=math.pi*math.pow(self.__radius,2)
    def output(self):
        print("Area :",self.__area)

class Rectangle(Shape):
    def __init__(self,len=0,br=0):
        self.__length=len
        self.__breadth=br
        self.__area = 0
    def input(self):
        self.__length=int(input("Enter Length:"))
        self.__breadth = int(input("Enter Breadth:"))
    def process(self):
        self.__area=self.__length*self.__breadth
    def output(self):
        print("Area :",self.__area)


def main():
    print("Circle Object:")
    c=Circle()
    c.input()
    c.process()
    c.output()

    print("\nRectangle Object:")
    r=Rectangle()
    r.input()
    r.process()
    r.output()
if __name__=="__main__":main()

Output

Circle Object: 
Enter radius:1.2 
Area : 4.523893421169302 
 
Rectangle Object:
Enter Length:2 
Enter Breadth:3
Area : 6