> 2) Topological sorting usually is well-defined on totally connected graphs, so I do not know what exactly it means to topologically sort two disjoint graphs. This was one of the main drawbacks of the tuple-based approach, but I think it may be a good property.

To give a use-case, I'm currently using topological sort to order a list of tasks where edges represent dependencies between tasks. Sometime a group of tasks does not share a dependency with another group any relative order between those two groups is correct:


A -> B

   C
  / \
 D   E
  \ /
   F

The order (A, B, C, D, E, F) would be correct in this example as would (C, A, E, B, D, F).

I think the general topological sort in Python should be able to handle such inputs.