设计一个三维向量类，并实现向量的加法、减法以及向量瑜标量的乘法和除法

 1 class vector3:
 2  def __init__(self, x_ = 0, y_ = 0, z_ = 0):
 3   self.x = x_
 4   self.y = y_
 5   self.z = z_
 6  def __add__(self, obj):
 7   return vector3(self.x+obj.x, self.y+obj.y, self.z+obj.z)
 8  def __sub__(self, obj):
 9   return vector3(self.x-obj.x, self.y-obj.y, self.z-obj.z)
10  def __mul__(self, obj):
11   return vector3(self.x*obj.x, self.y*obj.y, self.z*obj.z)
12  def __pow__(self, obj):
13   return vector3(self.y*obj.z-obj.y*self.z, self.z*obj.x-self.x*obj.z, self.x*obj.y-obj.x*self.y)
14  def __str__(self):
15   return str(self.x)+‘,‘+str(self.y)+‘,‘+str(self.z)
16 v1 = vector3(1, 2, 3)
17 v2 = vector3(0, 1, 2)
18 print (v1 + v2)
19 print (v1 - v2)
20 print (v1 * v2)
21 print (v1 ** v2)