def __missing__(self, key):
        if self.default_factory is None:
            raise KeyError(key)
        else:
            ret = self[key] = self.default_factory(name=key)
            return ret
def setPPSS(self, p1, p3, lenp1, lenp3):
        temp = []
        self.p1 = p1
        self.p3 = p3
        self.lenp1 = lenp1
        self.lenp3 = lenp3

        #bp3 is the angle beside p3 point, cp3 is the angle for line23, p2 is the output
        line31 = Line(p3, p1)
        self.lenp2 = line31.getR()
        #self.lenp2 = self.p3.distance(self.p1)
        #這裡是求角3
        ap3 = math.acos(((self.lenp1 * self.lenp1 + self.lenp2 * self.lenp2) - self.lenp3 * self.lenp3) / (2 * self.lenp1 * self.lenp2))
        #ap3 = math.acos(((self.lenp1 * self.lenp1 + self.lenp3 * self.lenp3) - self.lenp2 * self.lenp2) / (2 * self.lenp1 * self.lenp3))
        bp3 = line31.getT()
        cp3 = bp3 - ap3
        temp.append(p3.x + self.lenp1*math.cos(cp3))#p2.x
        temp.append(p3.y + self.lenp1*math.sin(cp3))#p2.y
        return temp