[igraph] Use C to manipulate Python iGraph edge attributes.

[Chris Cameron]

Dear list - 

I have some code in C that computes tie range for every edge in a C iGraph and 
store it as an attribute. 
(The tie range for an edge is the length of the shortest path with length 
greater than 2 between the two endpoints of that edge). 

I would like to use this code on graphs created in Python via a C extension but 
it looks to me like attributes for python graphs are stored in python and not 
in the underlying C data type that represents the graph. Am I mistaken (and 
there is a way to manipulate the attributes directly from C) or should I focus 
on computing and returning a tie_range dictionary to python and then using the 
dict to update the python edge attributes dict. 

Thanks!
Christopher Cameron