[igraph] Python igraph weighted centrality error: unhandled type

[Triple A]

Dear all,

I am calculating weighted centrality measures using python-igraph.

from igraph import *
g = Graph.Read_Ncol("sample.txt",names=True,directed=False,weights=True)
print (g.vs["name"])
print (g.es["weight"])

Below are two lists of the vertices and edge weights in my network:

['a', 'b', 'c', 'd', 'e']
[4.0, 2.0, 3.0, 4.0, 4.0]

I am using following codes calculating weighted centrality:

print (g.strength(weights=True))
print (g.betweenness(weights=True))

Below is the error message I got:

TypeError: unhandled type

Can anyone let me know what went wrong? Thank you!

Claire