To the three undo strategies I mentioned yesterday, we can add a fourth: widget-level undo. Unlike the others, this one works entirely on the UI side. The basic idea is that since all UI flows through widets, all you need to do is keep track of when those widgets change. An implementation of this idea is provided by the gtkundo library.

This seems like a good appraoch for input dialogs. You can reverse even small user actions that never actually propagate changes back to the model with relatively little effort (since a library like gtkundo provides all the code necessary to handle stock widgets), but it won't work for the timeline canvas itself, since this is a custom UI element. In any case I don't see python bindings for this library, so it would be difficult for us to use it anyways.

The concept itself is useful, and I plan to study the code (which looks pretty simple).