面向对象组合思想的经典题

2，定义一个类，计算圆的周长和面积。
from math import pi
class Circle:
    def __init__(self,r):
        self.r = r
    def area(self):
        return round(self.r ** 2 * pi,2)
    def perimeter(self):
        return round(self.r * 2 * pi,2)
# c1 = Circle(5)
# print(c1.area())
# print(c1.perimeter())
# 3，定义一个圆环类，计算圆环的周长和面积（升级题）。
class Ring:
    def __init__(self,r1,r2):
        self.r1 = r1
        self.r2 = r2
    def area(self):
        return round(self.r1 ** 2 * pi - self.r2 ** 2 * pi, 2)
    def perimeter(self):
        return round(self.r1 * 2 * pi + self.r2 * 2 * pi, 2)
r1 = Ring(6,3)
print(r1.area())
print(r1.perimeter())
组合的思想
class Ring:
    def __init__(self,r1,r2):
        self.r1 = Circle(r1)
        self.r2 = Circle(r2)
    def area(self):
        return self.r1.area() - self.r2.area()
    def perimeter(self):
        return self.r1.perimeter() + self.r2.perimeter()
r = Ring(6,3)
print(r1.area())
print(r1.perimeter())