input: 
  class Vector3D:
      """
      Create a Python class which represents a 3D Vector. Initialize the vector with
      x, y, and z coordinates. The __str__ method should return a string representation
      of the vector in the format '(x, y, z)'.
      Example:
      vec = Vector3D(1.0, 2.0, 3.0)
      print(vec)
      (1.0, 2.0, 3.0)
      """
      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) + ")"
  
output:     
      def __add__(self, other):
          return Vector3D(self.x + other.x, self.y + other.y, self.z + other.z)
  
      def __sub__(self, other):
          return Vector3D(self.x - other.x, self.y - other.y, self.z - other.z)
  
      def __mul__(self, scalar):
          return Vector3D(self.x * scalar, self.y * scalar, self.z * scalar)
  
      def __rmul__(self, scalar):
          return self.__mul__(scalar)
  
      def __eq__(self, other):
          return self.x == other.x and self.y == other.y and self.z == other.z
  
      def __ne__(self, other):
          return not self.__eq__(other)
  