download python files from here Studio Python Modules

put python files in the same folder of .gh file

import and initialize in your code

import rhinoscriptsyntax as rs
import graph_1_2 as g

#create graph(network)
g.initFromCrv(crv)
print g

graph_test.3dm
graph_test1.gh

actual code of get shortest path in network and visualize the path

import rhinoscriptsyntax as rs
import graph_1_2 as g

#create graph(network)
g.initFromCrv(crv)
print g

#set origin node and destination node by rhino points
origin = g.closestNode(pt1)
destination = g.closestNode(pt2)
#for visualize o and d
origin_pt = origin.pos
destination_pt = destination.pos
#calc shortest distance from origin node to other nodes
g.Dijkstra(origin)
#get route edges from origin to destination
rtee = g.traceRouteEdge(destination)
print rtee

rte = []
for e in rtee:
    #get curve of edge from graph edge instance
    rte.append(e.cv)

shortest distance calculation by Dijkstra method (e / j )