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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 is_disconnected(self, node_id):
 """Check whether the node connection has been disconnected or failed. A disconnected node has either been closed or has failed. Connection failures are usually transient and can be resumed in the next ready() call, but there are cases where transient failures need to be caught and re-acted upon. Arguments: node_id (int):
 the id of the node to check Returns: bool: True iff the node exists and is disconnected """

        conn = self._conns.get(node_id)
        if conn is None:
            return False
        return conn.disconnected()