I think doctest and a UI around the doctest concept (there have been a couple) is a better approach. There was one whose name I can't remember – r...something.

I think doctest and a UI around the doctest concept (there have been a couple) is a better approach. There was one whose name I can't remember – r...something. Unfortunately it used wxWindows, and was a pain to install... native UIs suck. But with a Doctest model you just develop a script, and if you change something rerun the script, starting where you left off (assuming the script reruns – if it doesn't then you probably want to start where it fails). You can extend the script without reloading still, but changing the past requires starting over... but it's just CPU cycles, assuming you aren't doing something computationally expensive. But even if so, you could have a kind of cross-session Pickling memoize function if you don't want to recalculate things. These reloading tricks are fragile and break in weird ways, like it won't fix badly initialized data, or classes that can't be upgraded because of state changes. It leads ultimately to a distrust of the environment, until you throw your hands up and go back to the old restart-frequently model like everyone else. Recursive reloading certainly isn't new, but it's never satisfying.