find nodes with multiple parents using networkx - networkx

Question

Let's say I have a directed graph (this is about relational tables). I want to find M:N tables to track relationships enabled thru M:N tables.
from pathlib import Path
import subprocess
import networkx as nx
def write_svg(g, name):
temp = "temp.dot"
suffix = "jpg"
nx.nx_agraph.write_dot(g, temp)
pa_img = Path(f"{name}.{suffix}")
li_cmd = f"/opt/local/bin/dot {temp} -T {suffix} -o {pa_img}".split()
subprocess.check_output(li_cmd)
G = nx.DiGraph()
G.add_edge("C1", "P1")
G.add_edge("C2", "P1")
G.add_edge("C21", "C2")
G.add_edge("MN12", "P1")
G.add_edge("MN12", "P2")
G.add_nodes_from([
("MN12", {"color" : "red"})
])
Run this, and I get:
So what I am considering here is that MN12 has as parents P1 and P2. So I want to consider P2 to be related to P1, with MN12 as the mapping table.
In other words, if I hard-code the relationship graph I want:
G = nx.DiGraph()
G.add_edge("C1", "P1")
G.add_edge("C2", "P1")
G.add_edge("C21", "C2")
G.add_edge("P2(using MN12)", "P1")
G.add_nodes_from([
("P2(using MN12)", {"color" : "green"})
])
Note that C21 remains a child of C2. Only MN12 is modified, because it has 2 parents.
Now, I know I can see the degree of a given node.
Going in back to my input graph:
(Pdb++) G.degree('MN12')
2
(Pdb++) G.degree('C1')
1
(Pdb++) G.degree('C2')
2
(Pdb++) G.degree('P1')
3
But how do I see that the arrows from MN12 go towards both P1 and P2? Is this even a question for networkx?

Answer 1

You can use both out_edges and successors.
>>> G.out_edges("MN12")
OutEdgeDataView([('MN12', 'P1'), ('MN12', 'P2')])
>>> list(G.successors("MN12"))
['P1', 'P2']