Simple depth first traversal on a graph

graph_dfs.py

 def dfs(self, start_node):
        """Recursive implementation
        of Depth First Search iterating through a node's edges.
        """
        ret_list = [start_node.value]
        start_node.visited = True
        edges_out = [e for e in start_node.edges
                     if e.node_to.value != start_node.value]
        for edge in edges_out:
            if not edge.node_to.visited:
                ret_list.extend(self.dfs_helper(edge.node_to))
        return ret_list