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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 nodes(self):
 """ This is a special derived_class relationship because NodeBalancerNode is the only api object that requires two parent_ids """

        if not hasattr(self, '_nodes'):
            base_url = "{}/{}".format(NodeBalancerConfig.api_endpoint, NodeBalancerNode.derived_url_path)
            result = self._client._get_objects(base_url, NodeBalancerNode, model=self, parent_id=(self.id, self.nodebalancer_id))

            self._set('_nodes', result)

        return self._nodes