List of gc-tracked objects owned by this ObjectGraph instance.

def owned_objects(self):
        """
        List of gc-tracked objects owned by this ObjectGraph instance.

        """
        return (
            [
                self,
                self.__dict__,
                self._head,
                self._tail,
                self._out_edges,
                self._out_edges._keys,
                self._out_edges._values,
                self._in_edges,
                self._in_edges._keys,
                self._in_edges._values,
                self._vertices,
                self._vertices._elements,
                self._edges,
            ] +
            list(six.itervalues(self._out_edges)) +
            list(six.itervalues(self._in_edges))
        )