def listeners(self, event):
return self._listeners[event][:] + self._once[event][:]<EOL>
Get an iterable of all listeners for the given event.

        Args:
            event (str): The name of the event for which to generate an
                iterable of listeners.

        The resulting iterable contains all listeners regardless of whether
        they were registered with 'on'/'add_listener' or 'once'.