Topological sort is actually reversed topological sort?
graph_tool.topology.topological_sort(g) creates "a linear ordering of the vertices such that if edge (u,v) appears in the graph, then v comes before u in the ordering".
However, topological sort is almost everywhere (except Boost Graph Library) defined as "linear ordering of vertices such that for every directed edge uv from vertex u to vertex v, u comes before v in the ordering".
I think it should be at least emphasised in documentation that it's not "real" topological sort. It's a bit confusing now.