Saving a deep copy of an object, then modifying it and saving another copy?

Question

I have a 'GameBoard' class and am doing a search on it. I want to save the current gameboard in a list, change the state of the gameboard, save THAT one in a list, and so on (so I would have incremental versions of the gameboard as a game progresses).

I'm currently doing this with copy.deepcopy, but it doesn't seem to be saving and moving on. Here is a sample of my code:

    moves = [] # just for reference.  this has at least one value in it by the time the while loop hits.
    while winner is False and len(moves) > 0:
        g_string = gb.to_string()
        if g_string == win_string:
            winner = True
            break

        possibilities = gb.legal_moves(visited) # returns a list of possible moves to take

        if len(possibilities) > 0:
            moves.append(copy.deepcopy(gb))
            gb.perform(possibilities[0]) # this modifies gb, according to the gameplay move.
            # snipped, for brevity.

If after 100 iterations, I were to print moves, I would get 100 identical objects. If I print the object each time before appending it, they are definitely different at the time of appending.

To clarify, I would like copies of these objects (for use in things like a graph, to perform DFS and BFS on)

Here is more of my GameBoard class

class GameBoard:
    number_of_rows = 3
    rows = []
    global random_puzzle

    def __init__(self, setup):
            #some code.  fills in the rows. adds some things to that list. etcetc..
            # more code

Answer 1

Your code is valid for a simple dictionary object:

seq = 1
a_dict = {}
moves = []
while seq < 4:
 a_dict['key' + str(seq)] = 'value' + str(seq)
 moves.append(copy.deepcopy(a_dict))
 seq = seq + 1

print moves

Somehow for your object, deepcopy does not reach the contents of your gameboard.

Is your gameboard data somehow stored outside of the object in which case only a pointer to it is copied? Which state of the board is saved, the first or the last one? Can you post more details about the structure of your object?

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EDIT: Try adding your own getstate/setstate methods in order to tell deepcopy what data needs to copied between instances. For example if your rows array contains the gameboard:

def __getstate__(self): 
    return self.rows

def __setstate__(self, rows): 
    self.rows = rows