When I try to read GraphML files written with python-igraph, I get the
following `RuntimeWarning`:
RuntimeWarning: Could not add vertex ids, there is already an 'id' vertex attribute at foreign-graphml.c:416
For example, consider the following simple [GraphML file][1]:
<?xml version="1.0" encoding="UTF-8"?>
<graphml xmlns="
http://graphml.graphdrawing.org/xmlns"
xmlns:xsi="
http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://graphml.graphdrawing.org/xmlns
http://graphml.graphdrawing.org/xmlns/1.0/graphml.xsd">
<graph id="G" edgedefault="undirected">
<node id="n0"/>
<node id="n1"/>
<edge id="e1" source="n0" target="n1"/>
</graph>
</graphml>
and a simple python script:
import igraph
G1 = igraph.Graph.Read_GraphML('wiki.graphml')
G1.write_graphml('wiki-ig.graphml')
G2 = igraph.Graph.Read_GraphML('wiki-ig.graphml')
which loads the original GraphML files, saves it to a new GraphML file, and
then tries to read back the just written file. Note the `RuntimeWarning` is
only generated on the second `Read_GraphML()`. Am I using `write_graphml()`
and/or `Read_GraphML()` incorrectly?
For reference, I am running Ubuntu 14.04 with python-igraph 0.7 from PyPI.