def yaml(self):
        return yaml.dump(self.serialized, default_flow_style=False,
                         encoding=None)
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)