#coding:utf-8
class Screen(object):
    @property
    def width(self):
        return self._width

    @width.setter
    def width(self, value):
        self._width = value # 起名加下划线是为了区分是函数还是变量，避免递归调用自己

    @property
    def height(self):
        return self._height

    @height.setter
    def height(self, value):
        self._height = value

    @property
    def resolution(self):
        return self.width * self.height

if __name__ == '__main__':
    s = Screen()
    s.width = 10
    s.height = 20
    print(s.resolution)