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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def on_connection_state_change(self, event_type, callback):
 """Register a callback for a specific connection state change. Register a callback to be triggered when the connection changes to the specified state, signified by a ConnectionEvent. The callback must be a coroutine. Args: event_type (ConnectionEvent):
 the connection event to listen for callback (coroutine):
 a coroutine to call on the event occurrence """

        listeners = self._connection_state_listeners.get(event_type, [])
        listeners.append(callback)
        self._connection_state_listeners[event_type] = listeners