input: from typing import List
  
  
  def generate_3D_vector_class(class_name: str) -> str:
      """ Generates a Python class string that represents a 3D Vector.
      The class should have an initializer that takes three parameters, x, y, and z,
      and a __str__ method that returns the vector in the format "(x, y, z)".
      
      Example:
      for generate_3D_vector_class('Vector3D') == '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 f'''class {class_name}:
      def __init__(self, x, y, z):
          self.x = x
          self.y = y
          self.z = z
      
      def __str__(self):
          return "(" + str(self.x) + ", " + str(self.y) + ", " + str(self.z) + ")"'''