Help with saving and restoring program state

[Kent Johnson]

Jacob H wrote:
> Hello list...
> 
> I'm developing an adventure game in Python (which of course is lots of
> fun). One of the features is the ability to save games and restore the
> saves later. I'm using the pickle module to implement this. Capturing
> current program state and neatly replacing it later is proving to be
> trickier than I first imagined, so I'm here to ask for a little
> direction from wiser minds than mine!
> 
> When my program initializes, each game object is stored in two places
> -- the defining module, and in a list in another module. The following
> example is not from my actual code, but what happens is the same.
> 
> (code contained in "globalstate" module)
> all_fruit = []
> 
> (code contained in "world" module)
> class Apple(object): # the class hierarchy goes back to object, anyway
>     def __init__(self):
>     	self.foo = 23
>     	self.bar = "something"
>     	globalstate.all_fruit.append(self)    	
> apple = Apple()
> 
> I enjoy the convenience of being able to refer to the same apple
> instance through world.apple or globalstate.all_fruit, the latter
> coming into play when I write for loops and so on. When I update the
> instance attributes in one place, the changes are reflected in the
> other place. But now comes the save and restore game functions, which
> again are simplified from my real code:

My understanding of pickle is that it will correctly handle shared references in the saved data. So 
if you pack all your global dicts into one list and pickle that list, you will get what you want. 
See code changes below:

> 
> (code contained in "saveload" module)
> import pickle
> import world
   import globalstate
> def savegame(path_to_name):
>     world_data = {}
>     for attr, value in world.__dict__.items():
>     	# actual code is selective about which attributes 
>     	# from world it takes -- I'm just keeping this 
>     	# example simple
>     	world_data[attr] = value
       the_whole_shebang = [ world_data, globalstate.all_fruit, globalstate.all_items ]
>     fp = open(path_to_name, "w")
       pickle.dump(the_whole_shebang, fp)
>     fp.close()
>     
> def loadgame(path_to_name):
>     fp = open(path_to_name, "r")
       the_whole_shebang = pickle.load(fp)
       world_data, globalstate.all_fruit, globalstate.all_items = the_whole_shebang
>     for attr, value in world_data.items():
>     	setattr(world, attr, value)
>     fp.close()

Kent