I'm literally banging my head against a wall here (as in, yes, physically, at my current location, I am damaging my cranium). Basically, I've got a Python/Pygame game with some typical game "rooms", or "screens." EG title screen, high scores screen, and the actual game room. Something bad is happening when I switch between rooms: the old room (and its various items) are not removed from memory, or from my event listener. Not only that, but every time I go back to a certain room, my number of event listeners increases, as well as the RAM being consumed! (So if I go back and forth between the title screen and the "game room", for instance, the number of event listeners and the memory usage just keep going up and up.

The main issue is that all the event listeners start to add up and really drain the CPU. I'm new to Python, and don't know if I'm doing something obviously wrong here, or what.

I will love you so much if you can help me with this!

Below is the relevant source code. Complete source code at http://www.necessarygames.com/my_games/betraveled/betraveled_src0328.zip

MAIN.PY

class RoomController(object):
    """Controls which room is currently active (eg Title Screen)"""

    def __init__(self, screen, ev_manager):
        self.room = None
        self.screen = screen
        self.ev_manager = ev_manager
        self.ev_manager.register_listener(self)
        self.room = self.set_room(config.room)

    def set_room(self, room_const):
        #Unregister old room from ev_manager
        if self.room:
            self.room.ev_manager.unregister_listener(self.room)
            self.room = None
        #Set new room based on const
        if room_const == config.TITLE_SCREEN:
            return rooms.TitleScreen(self.screen, self.ev_manager)
        elif room_const == config.GAME_MODE_ROOM:
            return rooms.GameModeRoom(self.screen, self.ev_manager)        
        elif room_const == config.GAME_ROOM:
            return rooms.GameRoom(self.screen, self.ev_manager)
        elif room_const == config.HIGH_SCORES_ROOM:
            return rooms.HighScoresRoom(self.screen, self.ev_manager)

    def notify(self, event):
        if isinstance(event, ChangeRoomRequest):
            if event.game_mode:
                config.game_mode = event.game_mode            
            self.room = self.set_room(event.new_room)

#Run game 
def main():
    pygame.init()
    screen = pygame.display.set_mode(config.screen_size)

    ev_manager = EventManager()
    spinner = CPUSpinnerController(ev_manager)
    room_controller = RoomController(screen, ev_manager)    
    pygame_event_controller = PyGameEventController(ev_manager)

    spinner.run()

EVENT_MANAGER.PY

class EventManager:

    #This object is responsible for coordinating most communication
    #between the Model, View, and Controller.
    def __init__(self):
        from weakref import WeakKeyDictionary
        self.last_listeners = {}
        self.listeners = WeakKeyDictionary()
        self.eventQueue= []
        self.gui_app = None

    #----------------------------------------------------------------------
    def register_listener(self, listener):
        self.listeners[listener] = 1

    #----------------------------------------------------------------------
    def unregister_listener(self, listener):
        if listener in self.listeners:
            del self.listeners[listener]

    #----------------------------------------------------------------------
    def clear(self):
        del self.listeners[:]

    #----------------------------------------------------------------------
    def post(self, event):
#        if  isinstance(event, MouseButtonLeftEvent):
#            debug(event.name)
        #NOTE: copying the list like this before iterating over it, EVERY tick, is highly inefficient,
        #but currently has to be done because of how new listeners are added to the queue while it is running
        #(eg when popping cards from a deck). Should be changed. See: http://dr0id.homepage.bluewin.ch/pygame_tutorial08.html
        #and search for "Watch the iteration"

        print 'Number of listeners: ' + str(len(self.listeners))

        for listener in list(self.listeners):                               
            #NOTE: If the weakref has died, it will be 
            #automatically removed, so we don't have 
            #to worry about it.
            listener.notify(event)

    def notify(self, event):
        pass

#------------------------------------------------------------------------------
class PyGameEventController:
    """..."""
    def __init__(self, ev_manager):
        self.ev_manager = ev_manager
        self.ev_manager.register_listener(self) 
        self.input_freeze = False

    #----------------------------------------------------------------------
    def notify(self, incoming_event):

        if isinstance(incoming_event, UserInputFreeze):
            self.input_freeze = True

        elif isinstance(incoming_event, UserInputUnFreeze):
            self.input_freeze = False        

        elif isinstance(incoming_event, TickEvent) or isinstance(incoming_event, BoardCreationTick):

            #Share some time with other processes, so we don't hog the cpu
            pygame.time.wait(5)

            #Handle Pygame Events
            for event in pygame.event.get():
                #If this event manager has an associated PGU GUI app, notify it of the event
                if self.ev_manager.gui_app:
                    self.ev_manager.gui_app.event(event)
                #Standard event handling for everything else
                ev = None
                if event.type == QUIT:
                    ev = QuitEvent()
                elif event.type == pygame.MOUSEBUTTONDOWN and not self.input_freeze:
                    if event.button == 1:    #Button 1
                        pos = pygame.mouse.get_pos()
                        ev = MouseButtonLeftEvent(pos)
                elif event.type == pygame.MOUSEBUTTONDOWN and not self.input_freeze:
                    if event.button == 2:    #Button 2
                        pos = pygame.mouse.get_pos()
                        ev = MouseButtonRightEvent(pos)   
                elif event.type == pygame.MOUSEBUTTONUP and not self.input_freeze:
                    if event.button == 2:    #Button 2 Release
                        pos = pygame.mouse.get_pos()
                        ev = MouseButtonRightReleaseEvent(pos)                                              
                elif event.type == pygame.MOUSEMOTION:
                        pos = pygame.mouse.get_pos()
                        ev = MouseMoveEvent(pos)

                #Post event to event manager
                if ev:
                    self.ev_manager.post(ev)        

#        elif isinstance(event, BoardCreationTick):
#            #Share some time with other processes, so we don't hog the cpu
#            pygame.time.wait(5)               
#                           
#            #If this event manager has an associated PGU GUI app, notify it of the event
#            if self.ev_manager.gui_app:
#                self.ev_manager.gui_app.event(event)

#------------------------------------------------------------------------------            
class CPUSpinnerController:

    def __init__(self, ev_manager):
        self.ev_manager = ev_manager
        self.ev_manager.register_listener(self)
        self.clock = pygame.time.Clock()
        self.cumu_time = 0

        self.keep_going = True


    #----------------------------------------------------------------------
    def run(self):
        if not self.keep_going:
            raise Exception('dead spinner')        
        while self.keep_going: 
            time_passed = self.clock.tick()
            fps = self.clock.get_fps()
            self.cumu_time += time_passed
            self.ev_manager.post(TickEvent(time_passed, fps))

            if self.cumu_time >= 1000:
                self.cumu_time = 0
                self.ev_manager.post(SecondEvent(fps=fps))

        pygame.quit()


    #----------------------------------------------------------------------
    def notify(self, event):
        if isinstance(event, QuitEvent):
            #this will stop the while loop from running
            self.keep_going = False       

EXAMPLE CLASS USING EVENT MANAGER

class Timer(object):

    def __init__(self, ev_manager, time_left):
        self.ev_manager = ev_manager
        self.ev_manager.register_listener(self)
        self.time_left = time_left
        self.paused = False

    def __repr__(self):
        return str(self.time_left)

    def pause(self):
        self.paused = True

    def unpause(self):
        self.paused = False

    def notify(self, event):
        #Pause Event
        if isinstance(event, Pause):   
            self.pause() 
        #Unpause Event
        elif isinstance(event, Unpause):   
            self.unpause()                
        #Second Event
        elif isinstance(event, SecondEvent):   
            if not self.paused: 
                self.time_left -= 1