input: 
  def print_board():
      """Prints the current state of the Tic Tac Toe board.
      >>> board = ["X", "O", " ", " ", "X", "O", "O", "X", " "]
      >>> print_board()
  
      | X | O |   |
      |   | X | O |
      | O | X |   |
      """
      row1 = "| {} | {} | {} |".format(board[0], board[1], board[2])
      row2 = "| {} | {} | {} |".format(board[3], board[4], board[5])
      row3 = "| {} | {} | {} |".format(board[6], board[7], board[8])
  
      print()
      print(row1)
      print(row2)
      print(row3)
      print()
  
output:     global board
      board = ["X", "O", " ", " ", "X", "O", "O", "X", " "]