Copying an Object

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February 12th, 2012, 04:09 AM

Memeportal

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Copying an Object

With this function in board class.

def copy(self):
newBoard = Board()
return newBoard

How do I alter this function so newBoard satisfies

newBoard._board == self._board and at the same time

it should also hold

not (newBoard._board is self._board)

In other words returning a fresh copy of the board?

February 12th, 2012, 01:56 PM

b49P23TIvg

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Before we discover how to clone your object:

You have a couple functions like shown. That is, the __doc__ claims the function will raise some exception if conditions warrant. It's true that these functions do what they say, BUT they also trap the exception within the same function, and the function ends up returning None. Is that your intent?

Code:

    def is_valid_move(self, move):
        """Check if a proposed move is valid. 
        A valid move is a move to a location that does not already
        contain either an 'X' or an 'O'.
        The parameter move must be an integer between (and including)
        move.MIN_MOVE and move.MAX_MOVE, or a MoveValueError exception
        will be raised. 
        """
        try:
            if move > move.MAX_MOVE or move < move.MIN_MOVE:
                raise MoveValueError
            else:
                return self._board[move - 1] not in 'XO'
        except:
            pass

February 12th, 2012, 02:25 PM

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Yes, that was my intent. Would it not work if it traps the exception within the function?

February 12th, 2012, 02:54 PM

b49P23TIvg

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I give up. To clone an object you could recursively duplicate everything within it. Maybe the shelve module incorporates deepcopy. You won't have to duplicate the implementation effort.

What scares you? Anyone clever enough to bypass your code and change the state while taking their turn is also clever enough to detect your attempt to trap the cheater. I suppose you could also enforce time limits and use the operating system with file modification times to make cheating super-duper difficult.

Anyway, how about this sort of option which makes cheating a little bit more difficult. Make a copy of the board---this is easy, it's a list---and then after getting the move verify that the board copy agrees with the official game.board?

You've got so much unimplemented stuff I didn't figure out your intent. Passing self.game to select_next_move didn't stop the program. But then again, I can't determine that much because you've got unrestricted exception traps that block useful diagnostics.

Code:

        # make a copy of the board in case the player
        # modified it..
        board = self.game.board_copy()
        move = player.select_next_move(self.game)
        while not self.game.is_valid_move(move):
            message = "Invalid choice. Please choose again."
            self._ui.display_error_message(message)
            move = player.select_next_move(self.game)
        if self.game.board != board:
            raise CheatingException('You lose cheater')
        return move