human
Solve the following python programming problem given the following code:
def connect(self, obj, trait_name) : 
    ' Connect the extension point to a trait on an object.

        This allows the object to react when contributions are added or
        removed from the extension point.

        fixme: It would be nice to be able to make the connection automatically
        but we would need a slight tweak to traits to allow the trait type to
        be notified when a new instance that uses the trait type is created.

        ' 
    def listener(extension_registry, event) : 
        ' Listener called when an extension point is changed. ' 
        if (event.index is not None) : 
            name = (trait_name + '_items') 
            old = Undefined 
            new = event 
else : 
            name = trait_name 
            old = event.removed 
            new = event.added 
obj.trait_property_changed (name, old, new) 
        return 
extension_registry = self._get_extension_registry (obj) 
    extension_registry.add_extension_point_listener (listener, self.id) 
    listeners = self._obj_to_listeners_map.setdefault (self, { 
        
}) 
    listeners [trait_name] = listener 
    return 

    
    

    Fix the buggy line: listeners = self._obj_to_listeners_map.setdefault (self, {
assistant
#Here is Python code to fix the buggy line: listeners = self.

listeners = self._obj_to_listeners_map.setdefault (obj, {