docs: def get_parent_gradebook_nodes(self):
          """Gets the parents of this gradebook.
  
          return: (osid.grading.GradebookNodeList) - the parents of the
                  ``id``
          *compliance: mandatory -- This method must be implemented.*
  
          """
          parent_gradebook_nodes = []
          for node in self._my_map['parentNodes']:
              parent_gradebook_nodes.append(GradebookNode(
                  node._my_map,
                  runtime=self._runtime,
                  proxy=self._proxy,
                  lookup_session=self._lookup_session))
          return GradebookNodeList(parent_gradebook_nodes)