Quick and dirty line graph construction for multidigraphs.

line_graph.py

import networkx as nx

def line_graph(G, create_using=None):
    # This code works only for multidigraphs

    if create_using is None:
        L = G.__class__()
    else:
        # Already instantiated.
        L = create_using

    for u, v, key, data in G.out_edges_iter(data=True, keys=True):
        node = (u, v, key)
        L.add_node(node)

    for from_node in L.nodes_iter():
        # The to_node of the original machine determines the new edges
        edges = G.out_edges_iter(from_node[1], data=True, keys=True)
        for u, v, key, data in edges:
            to_node = (u, v, key)
            L.add_edge(from_node, to_node)

    return L

def test1():
    G = nx.MultiDiGraph()
    G.add_edges_from([(0,0), (0,1), (1,0), (1,1)])
    nx.draw_pydot(G)
    L = line_graph(G)
    nx.draw_pydot(L)

def test2():
    G = nx.MultiDiGraph()
    G.add_edges_from([(0,0), (0,1), (1,0), (1,1), (0,1), (1,1)])
    nx.draw_pydot(G)
    L = line_graph(G)
    nx.draw_pydot(L)

test1()