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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 rollback(self, rb_id=1):
 """ Rollback the last committed configuration. :param rb_id: Rollback a specific number of steps. Default: 1 """

        rpc_command = '<Unlock/><Rollback><Previous>{rb_id}</Previous></Rollback><Lock/>'.format(rb_id=rb_id)
        self._execute_rpc(rpc_command)