Class cross referencing?

Question

I come from a C++ background and I am a bit lost without the whole pointer concept in python. Or at least it's unclear. For instance, I want to create a game of tick tack toe using OOP in Python. I have a couple classes like so:

class Game(object):
    def __init__(self, player1, player2):
        self.board = [['','',''],
                      ['','',''],
                      ['','','']]
        self.players = [player1, player2]

class Player(object):
    def __init__(self, game, marking):
        self.game = game
        self.marking = marking  # either 'X' or 'O'

It seems obvious that the game needs to have a reference to the two players and that a player is also part of a game, and should, therefore, have a reference to the game. However, the above code doesn't work because there is no way I can create a player without a creating a game first. But to create a game I need two players. I could add in these references afterwards by doing something like: player.game = some_game_reference but this seems unpythonic and tedious to keep up with.

What is the best and most pythonic way of accomplishing this?

Answer 1

You can just have one class or the other updates its arguments. For example, create the players first, then have the game update the players with itself:

class Game(object):
    def __init__(self, player1, player2):
        self.board = [['','',''],
                      ['','',''],
                      ['','','']]
        self.players = [player1, player2]
        player1.game = self
        player2.game = self
        player1.marking = 'X'
        player2.marking = 'O'  

# Neither game nor marking make sense to set initially, until
# the players are added to a game.
class Player(object):
    def __init__(self):
        pass

p1 = Player()
p2 = Player()

g = Game(p1, p2)

(Whether you need this kind of coupling is, as others have pointed out, a separate design issue.)

Just to show the other direction is just as feasible:

class Player(object):
    def __init__(self, game, marking):
        self.game = game
        self.marking = marking
        game.players.append(self)

class Game(object):
    def __init__(self):
        self.board = [['','',''],
                      ['','',''],
                      ['','','']]

g = Game()
p1 = Player(g, 'X')
p2 = Player(g, 'O')

Hopefully, though, you'll agree that it makes more sense for the game to assign each player a marking. Here, you might try to add more than 2 players to a game, or add two X or two O players.