Finding Successors of Successors in a Directed Graph in NetworkX

Question

I'm working on some code for a directed graph in NetworkX, and have hit a block that's likely the result of my questionable programming experience. What I'm trying to do is the following:

I have a directed graph G, with two "parent nodes" at the top, from which all other nodes flow. When graphing this network, I'd like to graph every node that is a descendant of "Parent 1" one color, and all the other nodes another color. Which means I need a list Parent 1's successors.

Right now, I can get the first layer of them easily using:

descend= G.successors(parent1)

The problem is this only gives me the first generation of successors. Preferably, I want the successors of successors, the successors of the successors of the successors, etc. Arbitrarily, because it would be extremely useful to be able to run the analysis and make the graph without having to know exactly how many generations are in it.

Any idea how to approach this?

Answer 1

You don't need a list of descendents, you just want to color them. For that you just have to pick a algorithm that traverses the graph and use it to color the edges.

For example, you can do

from networkx.algorithms.traversal.depth_first_search import dfs_edges

G = DiGraph( ... )
for edge in dfs_edges(G, parent1):
    color(edge)

See https://networkx.github.io/documentation/stable/reference/algorithms/generated/networkx.algorithms.traversal.depth_first_search.dfs_edges.html?highlight=traversal

Answer 2

If you want to get all the successor nodes, without passing through edges, another way could be:

import networkx as nx
G = DiGraph( ... )
successors = nx.nodes(nx.dfs_tree(G, your_node))

I noticed that if you call instead:

successors = list(nx.dfs_successors(G, your_node)

the nodes of the bottom level are somehow not included.