定义一个圆类

定义一个类：圆形，该类有半径，周长，面积等属性，将半径隐藏起来，将周长与面积开放

import math
class circle:
    def __init__(self, rad):
        self.__rad=rad
        # self.perimeter=perimeter
        # self.area=area
    @property
    def perimeter(self):
        return self.__rad * math.pi * 2

    @property
    def area(self):
        return math.pi * self.__rad**2

c=circle(10)
print(c.area)
print(c.perimeter)