Drawing multiple edges between two nodes with networkx

Question

I need to draw a directed graph with more than one edge (with different weights) between two nodes. That is, I have nodes A and B and edges (A,B) with length=2 and (B,A) wit

Answer 1

You can use matplotlib directly using the node positions you have calculated.

G=nx.MultiGraph ([(1,2),(1,2),(1,2),(3,1),(3,2)])
pos = nx.random_layout(G)
nx.draw_networkx_nodes(G, pos, node_color = 'r', node_size = 100, alpha = 1)
ax = plt.gca()
for e in G.edges:
    ax.annotate("",
                xy=pos[e[0]], xycoords='data',
                xytext=pos[e[1]], textcoords='data',
                arrowprops=dict(arrowstyle="->", color="0.5",
                                shrinkA=5, shrinkB=5,
                                patchA=None, patchB=None,
                                connectionstyle="arc3,rad=rrr".replace('rrr',str(0.3*e[2])
                                ),
                                ),
                )
plt.axis('off')
plt.show()

Answer 2

An improvement to the reply above is adding the connectionstyle to nx.draw, this allows to see two parallel lines in the plot:

import networkx as nx
import matplotlib.pyplot as plt
G = nx.DiGraph() #or G = nx.MultiDiGraph()
G.add_node('A')
G.add_node('B')
G.add_edge('A', 'B', length = 2)
G.add_edge('B', 'A', length = 3)

pos = nx.spring_layout(G)
nx.draw(G, pos, with_labels=True, connectionstyle='arc3, rad = 0.1')
edge_labels=dict([((u,v,),d['length'])
             for u,v,d in G.edges(data=True)])

plt.show()

Answer 3

Add the following code to AMangipinto's solution to add edge labels in both directions (see link for picture):

edge_labels = dict([((u, v,), f'{d["length"]}\n\n{G.edges[(v,u)]["length"]}')
                for u, v, d in G.edges(data=True) if pos[u][0] > pos[v][0]])

nx.draw_networkx_edge_labels(G, pos, edge_labels=edge_labels, font_color='red')

The "if pos[u][0] > pos[v][0]" only adds an edge label in one direction. We add both lengths to the single label otherwise we would over write the first label on an edge. Note: The label won't show if the nodes have the same x position.

plot with edge labels

Answer 4

Try the following:

import networkx as nx
import matplotlib.pyplot as plt
G = nx.DiGraph() #or G = nx.MultiDiGraph()
G.add_node('A')
G.add_node('B')
G.add_edge('A', 'B', length = 2)
G.add_edge('B', 'A', length = 3)

pos = nx.spring_layout(G)
nx.draw(G, pos)
edge_labels=dict([((u,v,),d['length'])
             for u,v,d in G.edges(data=True)])
nx.draw_networkx_edge_labels(G, pos, edge_labels=edge_labels, label_pos=0.3, font_size=7)
plt.show()

This will return you this graph with two edges and the length shown on the edge: