def betweenness_centrality(self, normalized=True):
bc = proximity.brandes_betweenness_centrality(self, normalized)<EOL>for id, w in bc.items(): self[id]._betweenness = w<EOL>return bc<EOL>
Calculates betweenness centrality and returns an node id -> weight dictionary.
        Node betweenness weights are updated in the process.