[graph-tool] Nested loop over graph objects.

Hi, given a set graph_db of graphs, I want to compare the vertices of each graph with the vertices of each other graph from graph_db. Naturally, this results in a fourfold nested loop. Unfortunately , this is really slow in python. Is there a way to way to speed up this process. I tried iterating over indices of graph objects instead of graph objects itself, but this doesn't improve performance. Best regards Christopher