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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 listen_to_node(self, id_):
 """Attach a callback on the job pubsub if it exists"""

        if r_client.get(id_) is None:
            return
        else:
            self.toredis.subscribe(_pubsub_key(id_), callback=self.callback)
            self._listening_to[_pubsub_key(id_)] = id_
            return id_