game.py

class GameError(Exception):
    pass

class Game(object):

    def __init__(self):
        # "Board" is a 3x3 array of arrays, each value is whether 'X', 'O' or None
        self._board = None
        # Current player: 'X' or 'O'
        self._current_player = None
        self._game_started = False
        self.startGame()

    def startGame(self):
        """Start a new game"""
        self._resetBoard()
        self._current_player = 'X'
        self._game_started = True

    def _resetBoard(self):
        """Clear the board (reset all cells to None)"""
        row = [None] * 3
        self._board = [row[:], row[:], row[:]]

    def getCell(self, x, y):
        """Returns value of the cell with given coordinates: 'X', 'O' or None"""
        x, y = int(x), int(y)
        self._checkCoords(x, y)
        return self._board[x - 1][y - 1]
	
    # Return the array filled with 'X', 'O' or None
    def getBoard(self):
        return self._board
    board = property(getBoard)

    # Returns the Current Player value: 'X' or 'O'
    def getCurrentPlayer(self):
        return self._current_player
    current_player = property(getCurrentPlayer)

    # Sets given value 'X' or 'O' to given cell
    def _setCell(self, x, y, value):
        x, y = int(x), int(y)
        self._checkCoords(x, y)
	# Raise Exception if the value is other than 'X' or 'O'
        if value not in ('X', 'O'):
            raise ValueError('Cell value must be whether "{0}" or "{1}"'.format('X', 'O'))
	# Raise Exception if cell already has a value ie, 'X' or 'O'
        if self._board[x - 1][y - 1] is not None:
            raise ValueError("Cell is not empty")

        self._board[x - 1][y - 1] = value

    # Check for bounds of cell coordinates
    def _checkCoords(self, x, y):
	# Raise Exception if x coordinate is out of bounds
        if (x < 1) or (3 < x):
            raise ValueError("X must be between 1 and 3, got {0} instead".format(x))
        # Raise Exception if y coordinate is out of bounds
	if (y < 1) or (3 < y):
            raise ValueError("Y must be between 1 and 3, got {0} instead".format(y))

    # Called to make a move by the client
    def makeMove(self, x, y):
        """Make a move and switch to the next player"""

	# Exceptions for entries before game begins or after it ends
        if not self.isStarted():
            raise GameError("Can't make a move: game is not started")

        if self.isFinished():
            raise GameError("Can't make a move: game is finished")

        self._setCell(x, y, self._current_player)

	# After move by current player, change current player
        if self._current_player == 'X':
            self._current_player = 'O'
        else:
            self._current_player = 'X'

    def getWinner(self):
        """Returns 'X', 'O' or None (if game is not finished yet)"""
	
	# Making list of all possible rows, columns & diagonals 
        lines = []

        # Rows and cols
        for i in (1, 2, 3):
            lines.append([self.getCell(x, i) for x in (1, 2, 3)])
            lines.append([self.getCell(i, y) for y in (1, 2, 3)])

        # Diagonals
        lines.append([self.getCell(i, i) for i in (1, 2, 3)])
        lines.append([self.getCell(4 - i, i) for i in (1, 2, 3)])

        # Check each line
        for line in lines:
            if (line[0] == line[1] == line[2]) and (line[0] is not None):
                return line[0]

        #Checking for draw condition
        flag = 0
        for line in lines:
            if (line[0] != None) and (line[1] != None) and (line[2] != None):
                flag = 1
            else:
                flag = 0
                break
        if flag == 1:
            return 'D'

        return None

    def isStarted(self):
        return self._game_started

    def isFinished(self):
        return self.getWinner() is not None