How do I customize the display of edge labels in networkx?

This way it worked on my :

grafo_labels = nx.get_edge_attributes(G,'weight')

edges_label = nx.draw_networkx_edge_labels(G, pos, edge_labels = grafo_labels)

The command draw_networkx_edge_labels needs the argument edge_labels rather than labels.

So you need to change nx.draw_networkx_edge_labels(G, pos, labels = edge_labels) to nx.draw_networkx_edge_labels(G, pos, edge_labels = edge_labels)