from igraph import *

def network_height(net) :
  net.vs["height"] = [0]*len(net.vs)
  net.vs["visited"] = [False]*len(net.vs)
  Q = net.vs.select(_outdegree = 0).indices
  while (len(Q)>0) :
    j = Q[:1][0]
    Q = Q[1:]
    net.vs[j]["visited"] = True
    I = net.neighbors(j,"in")
    for i in I :
      net.vs[i]["height"] = max(net.vs[i]["height"],net.vs[j]["height"]+1)
      if all(net.vs.select(net.neighbors(i,"out"))["visited"]) :
         Q.append(i)
  print net.vs["height"]

g = Graph([(0,1), (0,2), (1,4), (1,3), (2,3), (2,6), (3,5)], True)
g.vs["name"]=["r","x","y","h","A","B","C"]

network_height(g)