Sorry for asking too much questions today about efficiency but it seems today is not my lucky day. I'm trying to build a graph by reading from a text file. The graph is 1034 vertices with 53498 edges. Creating this graph takes 6 seconds, so I was wondering if it truly takes that time or something is inefficient in my way of creating the graph. I have a text file that contains the edges in the format: vertex_label_x vertex_label_y. What I'm doing basically is maintaining a dictionary that maps from vertices labels in the text file to graph-tool vertices indices. When I read the file, I check if a label is in the dictionary, if so I retrieve its index from the dictionary. Otherwise I create a new vertex and store its index by the corresponding label in the dictionary. Then I create the edge using the indices of the source and target. I was wondering if my way is the wrong way to do that. This is my code: http://pastie.org/private/n9j7geizaosafmlimujca Many thanks in advance! Best.