import math


class Vector3D:
    def __init__(self, x, y, z):
        self.x:float = x
        self.y:float = y
        self.z:float = z

    def __sub__(self, other):
        return Vector3D(self.x - other.x, self.y - other.y, self.z - other.z)

    def __abs__(self) -> float:
        return (self.x ** 2 + self.y ** 2 + self.z ** 2) ** 0.5

    # 计算两向量间夹角
    def angle_to(self, other):
        return math.acos(
            abs(self.x * other.x + self.y * other.y + self.z * other.z)
            / abs(self)
            / abs(other)
        )