tictactoe.py

class TicTacToe:
    def __init__(self, first_player="x"):
        self.board = [[" " for _ in range(3)] for _ in range(3)]
        self.player = first_player
        self._turns = []

    @property
    def other_player(self):
        return {"x": "y", "y": "x"}[self.player]

    @property
    def turn_no(self):
        return len(self._turns)

    def play(self, y, x):
        if self.board[y][x] != " ":
            return
        self.board[y][x] = self.player
        self.player = self.other_player
        self._turns.append((y, x))

    def cancel(self):
        if not self._turns:
            return
        self.player = self.other_player
        y, x = self._turns.pop()
        self.board[y][x] = " "
        return y, x

    def plays(self):
        for y in range(3):
            for x in range(3):
                if self.board[y][x] == " ":
                    yield y, x

    def winner(self):
        b = self.board
        for y in range(3):
            if all(b[y][0] == b[y][x] != " " for x in (1, 2)):
                   return b[y][0]
        for x in range(3):
            if all(b[0][x] == b[y][x] != " " for y in (1, 2)):
                   return b[0][x]
        if all(b[0][0] == b[i][i] != " " for i in (1, 2)):
            return b[0][0]
        if all(b[2][0] == b[2-i][i] != " " for i in (1, 2)):
            return b[2][0]

    def draw(self):
        return not next(self.plays(), False)

    def __str__(self):
        out = []
        lines = iter(self.board)
        out.append("|".join(next(lines)))
        for line in lines:
            out.append("-+-+-")
            out.append("|".join(line))
        return "\n".join(out)

def minmax(ttt, maxi):
    if winner := ttt.winner():
        return 1 if winner == "y" else -1
    if ttt.draw():
        return 0

    scores = []
    for y, x in ttt.plays():
        ttt.play(y, x)
        scores.append(minmax(ttt, not maxi))
        ttt.cancel()
        #if maxi and scores[-1] == 1:
        #    return 1
        #if not maxi and scores[-1] == -1:
        #    return -1
    return max(scores) if maxi else min(scores)

def ai(ttt):
    scores = []
    for y, x in ttt.plays():
        ttt.play(y, x)
        scores.append(((y, x), minmax(ttt, False)))
        ttt.cancel()
        #if scores[-1] == 1:
        #    return y, x
    print(scores)
    best = max(scores, key=lambda t: t[1])[0]
    print("=>", best)
    return best

print("Human plays x, AI plays y")
ttt = TicTacToe(input("First player (x/y)? "))
print(ttt)
while True:
    #print(list(ttt.plays()))
    if ttt.player == "x":
        y, x = input("x: ").split()
    else:
        y, x = ai(ttt)
        print("y:", y, x)
    ttt.play(int(y), int(x))
    print(ttt)
    if winner := ttt.winner():
        print(winner, "wins!")
        break
    if ttt.draw():
        print("Draw!")
        break