import math


class Point:                   # this is the base class
    """Class that represents a point """

    def __init__(self, x=0, y=0):
        self.x = x
        self.y = y


class Circle(Point):            # is derived from Point
    """Class that represents a circle """

    def __init__(self, x=0, y=0, radius=0):
        Point.__init__(self, x, y)
        self.radius = radius

    def area(self):
        return math.pi * self.radius ** 2


class Cylinder(Circle):         # is derived from Circle
    """Class that represents a cylinder"""

    def __init__(self, x=0, y=0, radius=0, height=0):
        Circle.__init__(self, x, y, radius)
        self.height = height

    def volume(self):
        return self.area() * self.height


if __name__ == "__main__":
    d = Circle(0, 0, 1)
    print(d.area())
    print("attributes of circle object are")
    print(dir(d))
    c = Cylinder(0, 0, 1, 2)
    print(c.volume())
    print("attributes of cylinder object are")
    print(dir(c))