3x3 Tic Tac Toe

tictactoe.py

#! python
import random

def print_board(board, size):
    for j in range(0, size):
        marker = ""
        for i in range(0, size):
            saved = board.get((i, j))
            if saved:
                marker += saved + " "
            else:
                marker += "_" + " "

        print marker

def valid_input(input, board):
    try:
        for i in input:
            i = int(i)
            if i < 0 or i > 2:
                print "\tInvalid input. Move outside bounds"
                return False
    except ValueError:
        print "\tInvalid input. Please use the form x, y"
        return False
    return True

def clean_input(input):
    input = [int(i) for i in input]
    return tuple(input)

def find_winning_chain(move, board, size):
    x = move[0]
    y = move[1]

    winning = [
        [(0,0), (1,0), (2,0)],
        [(0,1), (1,1), (2,1)],
        [(0,2), (1,2), (2,2)],

        [(0,0), (0,1), (0,2)],
        [(1,0), (1,1), (1,2)],
        [(2,0), (2,1), (2,2)],

        [(0,0), (1,1), (2,2)],
        [(2,0), (1,1), (0,2)]
    ]

    for win in winning:
        if move in win and board.get(win[0]) == board.get(win[1]) == board.get(win[2]):
            return True

    return False


if __name__ == "__main__":
    game_on = True
    current_player = "X"
    other_player = "O"
    computer_player = "O"

    board = {}
    board_size = 3

    untaken_moves = set()
    for i in range(0, board_size):
        for j in range(0, board_size):
            untaken_moves.add((j, i))

    while game_on:
        print_board(board, board_size)

        turn_message = "Player " + str(current_player) + "'s turn. Make your move: "

        if current_player == computer_player:
            move = random.sample(untaken_moves, 1)[0]
        else:
            move = raw_input(turn_message).split(',')

            if not valid_input(move, board):
                continue

            move = clean_input(move)
            if move not in untaken_moves:
                print "\tMove already taken!"
                continue
        untaken_moves.remove(move)
        board[move] = current_player

        if find_winning_chain(move, board, board_size):
            game_on = False
            print "Tic tac toe! Congrats Player " + current_player + "!"
            continue
        if len(board.keys()) == board_size*board_size:
            game_on = False
            print "It's a tie!"
            continue

        temp = other_player
        other_player = current_player
        current_player = temp