stress centrality in social network - networkx

Question

i got the error of this code which is:
path[index][4] += 1
IndexError: list index out of range
why this happened?how can i remove this error ?
Code:
def stress_centrality(g):
stress = defaultdict(int)
for a in nx.nodes_iter(g):
for b in nx.nodes_iter(g):
if a==b:
continue
pred = nx.predecessor(G,b) # for unweighted graphs
#pred, distance = nx.dijkstra_predecessor_and_distance(g,b) # for weighted graphs
if a not in pred:
return []
path = [[a,0]]
path_length = 1
index = 0
while index >= 0:
n,i = path[index]
if n == b:
for vertex in list(map(lambda x:x[0], path[:index+1]))[1:-1]:
stress[vertex] += 1
if len(pred[n]) >i:
index += 1
if index == path_length:
path.append([pred[n][i],0])
path_length += 1
else:
path[index] = [pred[n][i],0]
else:
index -= 1
if index >= 0:
path[index][4] += 1
return stress

Answer 1

Without the data it's hard to give you anything more than an indicative answer.
This line
path[index][4] += 1
assumes there are 5 elements in path[index] but there are fewer than that. It seems to me that your code only assigns or appends to path lists of length 2. As in
path = [[a,0]]
path.append([pred[n][i],0])
path[index] = [pred[n][i],0]
So it's hard to see how accessing the 5th element of one of those lists could ever be correct.
This is a complete guess, but I think you might have meant
path[index][1] += 4