docs: def get_nodes(self, id_, ancestor_levels=10, descendant_levels=10, include_siblings=False):
          """Gets a portion of the hierarchy for the given ``Id``.
  
          arg:    id (osid.id.Id): the ``Id`` to query
          arg:    ancestor_levels (cardinal): the maximum number of
                  ancestor levels to include. A value of 0 returns no
                  parents in the node.
          arg:    descendant_levels (cardinal): the maximum number of
                  descendant levels to include. A value of 0 returns no
                  children in the node.
          arg:    include_siblings (boolean): ``true`` to include the
                  siblings of the given node, ``false`` to omit the
                  siblings
          return: (osid.hierarchy.Node) - a node
          raise:  NotFound - ``id`` is not found
          raise:  NullArgument - ``id`` is ``null``
          raise:  OperationFailed - unable to complete request
          raise:  PermissionDenied - authorization failure
          *compliance: mandatory -- This method must be implemented.*
  
          """
          # This impl ignores include_siblings, assumes false
          include_siblings = bool(include_siblings)
          parent_node_list = []
          child_node_list = []
          if ancestor_levels != 0:
              for parent_id in self.get_parents(id_):
                  parent_node_list.append(self.get_nodes(parent_id, ancestor_levels - 1, 0))
          if descendant_levels != 0:
              for child_id in self.get_children(id_):
                  child_node_list.append(self.get_nodes(child_id, 0, descendant_levels - 1))
          return objects.Node({'type': 'OsidNode',
                               'id': str(id_),
                               'childNodes': child_node_list,
                               'parentNodes': parent_node_list,
                               'root': not self.has_parents(id_),
                               'leaf': not self.has_children(id_),
                               'sequestered': False})