input: def Vector3D_class() -> str:
      """
      Create a Python class which represents a 3D Vector.
  
      >>> Vector3D_class()
      'class Vector3D:\\n    def __init__(self, x, y, z):\\n        self.x = x\\n        self.y = y\\n        self.z = z\\n    \\n    def __str__(self):\\n        return "(" + str(self.x) + ", " + str(self.y) + ", " + str(self.z) + ")"'
      """
output:     return 'class Vector3D:\n    def __init__(self, x, y, z):\n        self.x = x\n        self.y = y\n        self.z = z\n    \n    def __str__(self):\n        return "(" + str(self.x) + ", " + str(self.y) + ", " + str(self.z) + ")"'