TicTacToe

#!/usr/bin/env python
#Filename: tic-tac-toe.py
#Description: Tic-Tac-Toe two player game

class GAME:

    def __init__(self):
        '''Initialize parameters - the game board, moves stack and winner'''

        self.board = [ '-' for i in range(0,9) ]
        self.lastmoves = []
        self.winner = None

    def print_board(self):
        '''Print the current game board'''

        print "\nCurrent board:"

        for j in range(0,9,3):
            for i in range(3):
                if self.board[j+i] == '-':
                    print "%d |" %(j+i),
                else:
                    print "%s |" %self.board[j+i],

            print "\n",


    def get_free_positions(self):
        '''Get the list of available positions'''

        moves = []
        for i,v in enumerate(self.board):
            if v=='-':
                moves.append(i)
        return moves

    def mark(self,marker,pos):
        '''Mark a position with marker X or O'''
        self.board[pos] = marker
        self.lastmoves.append(pos)

    def revert_last_move(self):
        '''Reset the last move'''

        self.board[self.lastmoves.pop()] = '-'
        self.winner = None

    def is_gameover(self):
        '''Test whether game has ended'''

        win_positions = [(0,1,2), (3,4,5), (6,7,8), (0,3,6),(1,4,7),(2,5,8), (0,4,8), (2,4,6)]

        for i,j,k in win_positions:
            if self.board[i] == self.board[j] == self.board[k] and self.board[i] != '-':
                self.winner = self.board[i]
                return True

        if '-' not in self.board:
            self.winner = '-'
            return True

        return False

    def play(self,player1,player2):
        '''Execute the game play with players'''

        self.p1 = player1
        self.p2 = player2

        for i in range(9):

            self.print_board()

            if i%2==0:
                if self.p1.type == 'H':
                    print "\t\t[Human's Move]"
                else:
                    print "\t\t[Computer's Move]"

                self.p1.move(self)
            else:
                if self.p2.type == 'H':
                    print "\t\t[Human's Move]"
                else:
                    print "\t\t[Computer's Move]"

                self.p2.move(self)

            if self.is_gameover():
                self.print_board()
                if self.winner == '-':
                    print "\nGame over with Draw"
                else:
                    print "\nWinner : %s" %self.winner
                return

class Human:
    '''Class for Human player'''

    def __init__(self,marker):
        self.marker = marker
        self.type = 'H'

    def move(self, gameinstance):

        while True:

            m = raw_input("Input position:")

            try:
                m = int(m)
            except:
                m = -1

            if m not in gameinstance.get_free_positions():
                print "Invalid move. Retry"
            else:
                break

        gameinstance.mark(self.marker,m)

class AI:
    '''Class for Computer Player'''

    def __init__(self, marker):
        self.marker = marker
        self.type = 'C'

        if self.marker == 'X':
            self.opponentmarker = 'O'
        else:
            self.opponentmarker = 'X'

    def move(self,gameinstance):
        move_position,score = self.maximized_move(gameinstance)
        gameinstance.mark(self.marker,move_position)



    def maximized_move(self,gameinstance):
        ''' Find maximized move'''
        bestscore = None
        bestmove = None

        for m in gameinstance.get_free_positions():
            gameinstance.mark(self.marker,m)

            if gameinstance.is_gameover():
                score = self.get_score(gameinstance)
            else:
                move_position,score = self.minimized_move(gameinstance)

            gameinstance.revert_last_move()

            if bestscore == None or score > bestscore:
                bestscore = score
                bestmove = m

        return bestmove, bestscore

    def minimized_move(self,gameinstance):
        ''' Find the minimized move'''

        bestscore = None
        bestmove = None

        for m in gameinstance.get_free_positions():
            gameinstance.mark(self.opponentmarker,m)

            if gameinstance.is_gameover():
                score = self.get_score(gameinstance)
            else:
                move_position,score = self.maximized_move(gameinstance)

            gameinstance.revert_last_move()

            if bestscore == None or score < bestscore:
                bestscore = score
                bestmove = m

        return bestmove, bestscore

    def get_score(self,gameinstance):
        if gameinstance.is_gameover():
            if gameinstance.winner  == self.marker:
                return 1 # Won
            elif gameinstance.winner == self.opponentmarker:
                return -1 # Opponent won
        return 0 # Draw


if __name__ == '__main__':
    game=GAME()
    player1 = Human("X")
    player2 = AI("O")
    game.play( player1, player2)