Re: [igraph] Starting with python version

[Tamas Nepusz]

Hi Simone,

> I'm trying to start using Igraph python version. I'm getting some  
> troubles both because i'm a newbye programmer and Ican't find a  
> really good user guide like those written for Igraph C version.
The documentation for the Python interface is self-contained in the  
Python package, so you can simply use the Python help facility to get  
documentation on the objects and methods supported by the Python  
interface. E.g. try:

from igraph import *
help(Graph)

The HTML version of the documentation is available here:

http://cneurocvs.rmki.kfki.hu/igraph/doc/python/index.html

> but it doesn't work ... I get this message error:
>
> "Traceback (most recent call last):
> File "getting_net.py", line 17, in ?
> g=Graph(A,edges,directed=False)
> TypeError: List elements must be non-negative integer pairs"
The reason is that igraph expects the edge list to contain integer  
pairs. You are supplying strings instead of integers. Try the  
following line:

edges.append((int(split_line[0]), int(split_line[1]))

By the way, a more Pythonic way to do this is the following:

from igraph import *

SP_data = open("test_graph.dat", "r")
edgelist, weights = [], []
for line in SP_data:
  parts = line.strip().split()
  edgelist.append((int(parts[0]), int(parts[1])))
  weights.append(float(parts[2]))
SP_data.close()

g = Graph(edgelist)    # directed=False is the default
g.es["weight"] = weights

I haven't tried it, but it should work. You don't have to supply the  
number of vertices in the constructor of the graph, since igraph is  
able to infer it from the edge list. An even easier way to do this is  
to recognize that the format you mentioned is exactly the NCOL format  
(see http://cneurocvs.rmki.kfki.hu/igraphbook/igraphbook- 
foreign.html, "Large Graph Layout Formats"), so theoretically the  
following should also work:

from igraph import *
g = Graph.Read_NCOL("test_graph.dat")

--
T.