Determining Blocks from a nested block model in an interactive window

Hi all,
I'm thrilled about using Graph-tool to do topic modeling (using Martin
Gerlach's code:

In order for this technique to really work well, I need some help here - to
be able to browse the graph (nested block model) using an interactive window
and identify the blocks with a mouse click (each block in this method is a
group of words, ie. a topic in this usecase).

As you'll see from my uploaded image, when I select a block on the
interactive graph, I'm not sure how to determine which block this is
referring to. I've written a callback method
(win.graph.connect("button_press_event", update_bfs), that is able to
extract /widget.picked/.
However, I'm not sure what this refers to. Is this an edge id?
I'd like a mouseclick on a block to then programmatically trigger searching
the hierarchy to print the block in the model (offscreen).