[Tutor] my newbie program

[david]

hello everyone and thanks for all your help and patience so far.
i finally understood about getting my rooms to share a map
object. now its a world object because there is a python function
called map. y'all probably knew that. anyway i am working on
my dig method and i am thinking my exits are all messed up.
i will be wanting to add doors both locked and unlocked next.
so if anyone can help with a better room exit. or any comments
at all. 

import string
import sys

class World:
    def __init__(self):
        self.grid={}
    def addRoom(self,room,x,y):
        if self.grid.has_key((x,y)):
            raise KeyError,"location occupied"
        self.grid[(x,y)]=room
    
class Room:
    world = World()
    def __init__(self,x,y):
        self.desc="a nondescript room"
        self.exits=[]
        self.world.addRoom(self,x,y)
        self.coords=(x,y)
    def dig(self,dir):
        pass

class Parser:
    pass

class Actor:
    def __init__(self,location):
        self.location=location
    def DoCommand(self,cmd):
        if cmd == 'look':
            print self.location.desc
        elif cmd == 'exit':
            sys.exit()
        else:
            print 'unknown command'

class Player(Actor):
    def act(self):
        cmd = string.lower(raw_input('>'))
        self.DoCommand(cmd)
        
startroom=Room(0,0)
newroom=Room(0,1)
me=Player(startroom)

while 1:
    me.act()