Writing game-state data...

Prasad, Ramit ramit.prasad at jpmorgan.com
Fri Nov 9 18:23:06 CET 2012

Graham Fielding wrote:
> Hey, folks, me again!
> I've been puzzling over this for a while now:
> I'm trying to write data to a file to save the state of my game using the following function:
> def save_game():
>     #open a new empty shelve (possibly overwriting an old one) to write the game data
>     file_object = open('savegame.sav', 'wb')
>     file['map'] = map
>     file['objects'] = objects
>     file['player_index'] = objects.index(player)  #index of player in objects list
>     file['inventory'] = inventory
>     file['game_msgs'] = game_msgs
>     file['game_state'] = game_state
>     file['stairs_index'] = objects.index(stairs)
>     file['dungeon_level'] = dungeon_level
>     file.close()
> However, while 'savegame.sav' is created in the directory I specify, the function dies on file['map'] = map.
> This is the end of the stack trace:
>   File "C:\Python Project\Roguelike.py", line 966, in save_game
>     file['map'] = map
> TypeError: 'type' object does not support item assignment

`file` is the built-in for file objects. I would say you need
to use file_object[] instead, but it is a file object
and is not meant for this usage. You can write directly
to a file but it is easier to use sqllite or shelve/pickle
libraries. I will use shelve in my example since your code
is already doing something similar. Do not forget to
import shelve in your own code.

def save():
    shelf = shelve.open('savegame.sav', protocol=2) 
            # Change pickle protocol if you use Python < 2.3
    shelf['map'] = map
    shelf['objects'] = objects
    shelf['player_index'] = objects.index(player)
    shelf['inventory'] = inventory
    shelf['game_msgs'] = game_msgs
    shelf['game_state'] = game_state
    shelf['stairs_index'] = objects.index(stairs)
    shelf['dungeon_level'] = dungeon_level

> Now, the map is randomly generated -- could that be an issue?

Both "file" and "map" are built-in keywords and using those
names for you own variables is called shadowing a built-in.
Shadowing a built-in can be interesting and useful but should
be avoided. Also, it seems like save() is not in a class nor
having anything passed in; are all the game states variables 
stored at the module level or something?

> Should I just scrap the current system and use pickle?

You are almost there, so I would not bother. Normally I would
use pickle over shelve; I have not needed any of the advantages 
of shelve and why use a library on top of pickle when I only
need pickle? Of course, YMMV.


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