Return the list of leaves not empty
        in the tree rooted at this node,
        in DFS order.

        :rtype: list of :class:`~aeneas.tree.Tree`

def leaves_not_empty(self):
        """
        Return the list of leaves not empty
        in the tree rooted at this node,
        in DFS order.

        :rtype: list of :class:`~aeneas.tree.Tree`
        """
        return [n for n in self.dfs if ((n.is_leaf) and (not n.is_empty))]