class TicTacToe:
    X = 'X'
    O = 'O'

    def __init__(self):
        self.board = [' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ']
        self.player1_turn = None
        self.player2_turn = None
        self.turn = self.X
        self.game_over = False

    def display_board(self):
        print(f'{self.board[0]} | {self.board[1]} | {self.board[2]}')
        print('---------')
        print(f'{self.board[3]} | {self.board[4]} | {self.board[5]}')
        print('---------')
        print(f'{self.board[6]} | {self.board[7]} | {self.board[8]}')

    def is_legal(self, move):
        if self.board[move] == ' ':
            return True
        else:
            print('This side is not empty!')
            return False

    def piece_p_1(self):
        if self.turn == self.X:
            self.player1_turn = self.X
        else:
            self.player1_turn = self.O
        return self.player1_turn

    def piece_p_2(self, player):
        if player == self.X:
            self.player2_turn = self.X
        else:
            self.player2_turn = self.O
        return self.player2_turn

    def set_player1(self, index):
        try:
            while (index > 8 or index < 0) and not self.is_legal(index):
                print('Input not correct!!!')
                print('Player 1 (0 - 8): ')
                index = int(input())
            else:
                self.board[index] = self.player1_turn
        except:
            print('ERROR')

    def set_player2(self, index):
        try:
            while (index > 8 or index < 0) and not self.is_legal(index):
                print('Input not correct!!!')
                print('Player 2 (0 - 8): ')
                index = int(input())
            else:
                self.board[index] = self.player2_turn
        except:
            print('ERROR')

    def game_loop(self):
        while True:
            p1 = self.piece_p_1()
            p2 = self.piece_p_2(p1)

            self.display_board()

            if p1 == self.X:
                print('Player 1 is first (0 - 8): ')
                index = int(input())
                self.set_player1(index)
            else:
                print('Player 2 is first (0 - 8): ')
                index = int(input())
                self.set_player2(index)

            if self.turn == self.X:
                self.turn = self.O
            else:
                self.turn = self.X


game = TicTacToe()
game.game_loop()