Tic-Tac-Toe with the computer player

ttt.py

import copy

board = {
    'A': [' ', ' ', ' '],
    'B': [' ', ' ', ' '],
    'C': [' ', ' ', ' '],
}


def print_board():
    for i in "ABC":
        print(" | {} | {} | {} |".format(*board[i]))


def check_winner_state(board, mark):

    for i in "ABC":
        if board[i] == [mark, mark, mark]:
            return True

    for j in [0,1,2]:
        if [board["A"][j], board["B"][j], board["C"][j]]  == [mark, mark, mark]:
            return True

    if [board["A"][0],board["B"][1],board["C"][2]] == [mark, mark, mark]:
        return True
    if [board["A"][2],board["B"][1],board["C"][0]] == [mark, mark, mark]:
        return True
    return False

players_marks = "XO"

print_board()

player_names = {}

for mark in players_marks:
    whatever = input("Enter your name for %s" % mark)
    player_names[mark] = whatever

def human_player(mark):
    return input("Enter turn {}: ".format(mark)).upper()

def computer_player(mark):
    # Try everything and see if you can win
    other_mark = set(players_marks) - set(mark)
    for i in 'ABC':
        for j in 0,1,2:
            _b = copy.deepcopy(board)
            if _b[i][j] != ' ':
                continue
            _b[i][j] = mark
            if check_winner_state(_b, mark):
                return i+str(j+1)

    # So, we can't win. Try not to lose
    for i in 'ABC':
        for j in 0,1,2:
            _b = copy.deepcopy(board)
            if _b[i][j] != ' ':
                continue
            _b[i][j] = other_mark
            if check_winner_state(_b, other_mark):
                return i+str(j+1)

    # fuck it
    for i in 'ABC':
        for j in 0,1,2:
            if board[i][j] == ' ':
                return i+str(j+1)

players = [computer_player, computer_player]

selector = 0
while True:

    turn = selector % 2

    mark = players_marks[turn]
    inp = players[turn](mark)
    if len(inp) != 2:   # A1
        print("Bad format: ", inp)
        continue

    x, y = inp
    if x not in "ABC" or y not in "123":
        print("Bad format: ", inp)
        continue
    y = int(y)-1

    if board[x][y] != ' ':
        print("Position taken: ", inp)
        continue

    # mark the input
    board[x][y] = mark

    print_board()

    if check_winner_state(board, mark):
       print("%s, you are the winner, congrats!" % player_names[mark])

       break

    if selector == 8:
       print("No more goes, no one wins, sorry :(")
       break

    selector += 1