input: 
  def create_tic_tac_toe() -> TicTacToe:
      """Create an instance of a TicTacToe game with a 3x3 board initialized with '_' in each cell,
      and with 'x' starting the game.
      
      Example:
      game = create_tic_tac_toe()
      game.display()
      >>> _ _ _
      >>> _ _ _
      >>> _ _ _
      """
  
output:     class TicTacToe:
          def __init__(self):
              self.board = [['_' for _ in range(3)] for _ in range(3)]
              self.current_player = 'x'
  
          def display(self):
              for row in self.board:
                  print(' '.join(row))
  
      return TicTacToe()