Basic tic tac toe

tictactoe.py

import numpy as np

class Board:
    def __init__(self):
        self.turn = 0
        self.state = np.full((3, 3), "_")
    def __str__(self):
        r = f"{self.player()}'s turn\n{self.state}'"
        if self.winner() is not None:
            r += f"\nWinner: {self.winner()}"
        return r
    def player(self):
        return ["x", "o"][self.turn % 2]
    def winner(self):
        for s in ["x", "o"]:
            c1 = ((self.state == s).sum(axis=0) == 3).any()
            c2 = ((self.state == s).sum(axis=1) == 3).any()
            d1 = (self.state.diagonal() == s).sum() == 3
            d2 = (np.fliplr(self.state).diagonal() == s).sum() == 3
            if c1 or c2 or d1 or d2:
                return s
    def is_finished(self):
        return self.winner() is not None
    def play(self, b):
        i, c = b.split(",")
        i, c = int(i.strip()), int(c.strip())
        if not (0 <= i <= 2):
            return False
        if not (0 <= c <= 2):
            return False
        if self.state[i][c] != "_":
            return False
        self.state[i][c] = self.player()
        self.turn += 1
        
        return True

c = Board()
while not c.is_finished():
    while not c.play(input('(x, y):')):
        pass
    print(c)