Draw curved network edges in python

draw_curved_edges.py

import numpy as np
import matplotlib.patches as mpatches
import networkx as nx
from matplotlib.patches import FancyArrowPatch as ArrowPath
from matplotlib.font_manager import FontProperties

def draw_curved_edges(edges, pos, ax, mu=0.05, edge_color="black", edge_width=1.0, alpha=1.0, arrow_scale=20.0, loopsize=0):
	
	"""
	
	Params
	---------------------------
	edges: Edge list
	pos  : Dict of position of nodes
	ax   : Axes
	mu   : Control the curvature
	edge_color : Color or list of color for each edge
	edge_width : Double
	alpha : Opacity
	loopsize: Size of self loops
	"""

	for v,edge in enumerate(edges):
		
		x1,y1 = pos[edge[0]]
		x2,y2 = pos[edge[1]]
		
		#If self loop
		if edge[0]==edge[1]:
			dv = 0.0
			theta = np.linspace(0.0,2.0*np.pi, 100)
			X = np.cos(theta)*loopsize+x1-loopsize
			Y = np.sin(theta)*loopsize+y1
		
			
		else:
			dv = mu
			if x1>x2:
				x1,y1 = pos[edge[1]]
				x2,y2 = pos[edge[0]]
				dv = -mu

			dx = x2
			dy = y2

			# Center to origin
			x1 -= dx
			x2 -= dx
			y1 -= dy
			y2 -= dy

			r = ((y2-y1)**2.0 + (x2-x1)**2.0)**(0.5)

			theta = np.arctan2(y1, x1)
			c, s = np.cos(theta), np.sin(theta)
			R = np.matrix('{} {}; {} {}'.format(c, -s, s, c))

			# Rotate
			x1 = x2 - r
			y1 = y2

			# Find parabola
			h = (x2+x1)/2.0
			k = y2+dv*r
			a = (y2-k)/((x2-h)**2.0)
			X = np.linspace(x1,x2,100)
			Y = a*(X-h)**2.0+k

			# Rotate the parabola and translate
			theta = np.pi+theta
			c, s = np.cos(theta), np.sin(theta)
			R = np.matrix('{} {}; {} {}'.format(c, -s, s, c))
			for u in range(len(X)):
				C1 = np.array([X[u], Y[u]])
				C1 = np.dot(R, C1)
				X[u], Y[u] = C1[0,0]+dx , C1[0,1]+dy
		
		color = edge_color
		if type(edge_color)==list:
			color = edge_color[v]

		edgewidth = edge_width
		if type(edge_width)==list:
			edgewidth = edge_width[v]
		
		middle_index = int(len(X)/2)
		posA = (X[middle_index-5], Y[middle_index-5])
		posB = (X[middle_index+5], Y[middle_index+5])
		if dv<0.0:
			u = posA
			posA = posB
			posB = u
		
		try:
			arrow = ArrowPath(posA=posA, posB=posB, mutation_scale=arrow_scale,color=color)
			ax.add_patch(arrow)
		except:
			True


		ax.plot(X,Y, "-", linewidth=edgewidth, color=color, zorder=0, alpha=alpha)
		

def draw_networks(G, pos, ax, mu=0.08, 
					edge_color="black", 
					edge_width=1.0, 
					edge_alpha=1.0,
					use_edge_weigth=True,
					node_width=1.0,
					node_size=80.0,
					node_border_color="#404040",
					node_color="#EDEDED",
					node_alpha=1.0, 
					arrow_scale=20.0, 
					loop_radius=0.0, 
					letter="",
					letter_fontsize=13,
					letter_pos=[0.87, 0.02],
					letter_color="black"):

	# Edges
	weights = [0]*len(G.edges())
	for i,edge in enumerate(G.edges()):
		weights[i] = G[edge[0]][edge[1]]['weight'] if use_edge_weigth else 1.0
		
	draw_curved_edges(G.edges(), pos, ax, 
					mu=mu, 
					edge_color=edge_color, 
					alpha = edge_alpha,
					arrow_scale=arrow_scale,
					loopsize=loop_radius,
					edge_width=weights)

	# Nodes
	nodes = nx.draw_networkx_nodes(G, pos, 
		ax=ax, 
		node_size=node_size, 
		node_color=node_color, 
		linewidths=node_width)
	nodes.set_edgecolor(node_border_color)
	
	# Letter
	font = FontProperties()
	font.set_weight('bold')
	ax.text(letter_pos[0], letter_pos[1], letter, 
			verticalalignment='bottom', 
			horizontalalignment='left', 
			transform=ax.transAxes, 
			fontproperties=font,
			color=letter_color, 
			fontsize=letter_fontsize)

	# Axis
	ax.axis('off')
	return

With arrows

Now included in DynamicaLab

Hey, Thank you for sharing this code... the generated graph is pretty nice.... Please can you give precision about the 'ax' entry... i didn't understand it. its not a classical axis feature, It has attributes like plotting (ax.plot(.)) and so on !!!