Thanks, Nick. Before your last comment, I haven't looked much into Pdb, instead focusing on profile.py and trace.py because they looked like simpler cases. I think the approach with CodeRunner objects would work just fine for profile and trace but Pdb uses run() inherited from Bdb. In order to make it work with a CodeRunner object, it seems run() would have to be reimplemented in Pdb (effectively becoming a 'runCodeRunner()'), and we could probably do without _runscript(). Is that what you had in mind?