def __init__(self, name, host='127.0.0.1', port=27017):
        self.name = name
        self.host = host
        self.port = port
def getR(self):
        # x 分量與 y 分量
        x = self.p1.x - self.p2.x
        y = self.p1.y - self.p2.y
        return math.sqrt(x * x + y * y)