human
Solve the following python programming problem given the following code:
def __init__(self, hs) : 
    self.hs = hs 
    self.user_to_user_stream = { 
        
} 
    self.room_to_user_streams = { 
        
} 
    self.appservice_to_user_streams = { 
        
} 
    self.event_sources = hs.get_event_sources () 
    self.store = hs.get_datastore () 
    self.pending_new_room_events = [] 
    self.clock = hs.get_clock () 
    hs.get_distributor ().observe ('user_joined_room', count_listeners._user_joined_room) 
    self.clock.looping_call (self.remove_expired_streams, self.UNUSED_STREAM_EXPIRY_MS) 
    self.replication_deferred = ObservableDeferred (defer.Deferred ()) 
    def count_listeners() : 
        all_user_streams = set () 
        for x in self.room_to_user_streams.values () : 
            all_user_streams |= x 
for x in self.user_to_user_stream.values () : 
            all_user_streams.add (x) 
for x in self.appservice_to_user_streams.values () : 
            all_user_streams |= x 
return sum ((stream.count_listeners () for stream in all_user_streams)) 
metrics.register_callback ('listeners', count_listeners) 
    metrics.register_callback ('rooms', (lambda : count (bool, self.room_to_user_streams.values ()))) 
    metrics.register_callback ('users', (lambda : len (self.user_to_user_stream))) 
    metrics.register_callback ('appservices', (lambda : count (bool, self.appservice_to_user_streams.values ()))) 

    
    

    Fix the buggy line: hs.get_distributor ().observe ('user_joined_room', count_listeners._user_joined_room)
assistant
#Here is Python code to fix the buggy line: hs.

hs.get_distributor ().observe ('user_joined_room', self._user_joined_room)