Allow edge style to be a list of styles for DiGraphs

[mgbckr]

Fixes issue where DiGraphs fail to allow a list of edge styles (or when enabling arrows=True for Graph):

import networkx as nx
import matplotlib.pyplot as plt

g = nx.DiGraph()
g.add_nodes_from([0,1,2])
g.add_edges_from([(0,1), (0,2)])

nx.draw_networkx_nodes(g, pos=[(0,0), (0,1), (1,0)])
nx.draw_networkx_edges(g, pos=[(0,0), (0,1), (1,0)], style=["-", "--"],)

This throws an error:

ValueError: Unrecognized linestyle: ['-', '--']

The proposed pull request fixes this issue.

[dschult]

Thanks for this idea and for the code! :}

Could you make the if/else logic match that for width which is just before your code for linestyle?
Also, could you add tests for ensure that it is working?

[mgbckr]

Hi Dan, updated the logic style and added some tests. Let me know if you need anything else.

[dschult]

This looks good to me!
Thanks!

[rossbar]

Thanks @mgbckr , this seems like an obvious improvement to me!

I had a couple suggestions about cleaning up the logic a bit and making the added tests a bit more rigorous. One other thing is that the style parameter in the Parameters list of the draw_networkx_edges docstring should be updated to reflect this change.

[rossbar]

Sounds good, thanks @mgbckr !