Initial node's ids when creating graph from edge list

Question

I wonder, where does the function Read_Edgelist store the original id's from the the edge list? or under which attribute name?

Assume that I am reading an edge list like:

1 2
2 1 
1 3

where the numbers 1,2,3 are the ids (or names) of the nodes. Where does the iGraph (python version) stores these ids? I tried retrieving these Ids from the attribute name or id but it did not work, as those two attributes, seemingly, must be explicitly defined.

Answer 1

Read_Edgelist assumes the node ids are the consecutive integers from 0 to m, where m is the maximum integer in the edge list. So there is "no need to store node ids."

For example, if your edgelist.txt is 1 3, this code

import igraph as ig
g = ig.Graph.Read_Edgelist("edgelist.txt")
print g.get_adjacency()

creates a graph with four nodes (0, 1, 2, 3) and prints

[[0, 0, 0, 0]
 [0, 0, 0, 1]
 [0, 0, 0, 0]
 [0, 0, 0, 0]]

See this answer if you do not want "intermediate" nodes to be created.

While the following is unnecessary for a graph with consecutive node ids starting with 0, one could access the node ids using VertexSeq and Vertex:

for v in g.vs:
  print v.index   # node id