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

class vector3:
 def __init__(self, x_ = 0, y_ = 0, z_ = 0):
  self.x = x_
  self.y = y_
  self.z = z_
 def __add__(self, obj):
  return vector3(self.x+obj.x, self.y+obj.y, self.z+obj.z)
 def __sub__(self, obj):
  return vector3(self.x-obj.x, self.y-obj.y, self.z-obj.z)
 def __mul__(self, obj):
  return vector3(self.x*obj.x, self.y*obj.y, self.z*obj.z)
 def __pow__(self, obj):
  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)
 def __str__(self):
  return str(self.x)+‘,‘+str(self.y)+‘,‘+str(self.z)
v1 = vector3(1, 2, 3)
v2 = vector3(0, 1, 2)
print (v1 + v2)
print (v1 - v2)
print (v1 * v2)
print (v1 ** v2)