It's like CSI vs Dr House. Debugging in python is forensic; you can figure out why your program died, but you can't really fix it. In common lisp, debugging can

It's like CSI vs Dr House. Debugging in python is forensic; you can figure out why your program died, but you can't really fix it. In common lisp, debugging can be curative as well as forensic. If you hit a problem like you call foo from bar, but foo isn't defined you can just write an implementation in your editor, send it to the running lisp and continue with the current execution. If a class is missing something, you can change the definition and not onl y have it take effect for all live instances, but you can also say how to transform the existing instances in your program. Have a look at the example given in the "docs": http://clhs.lisp.se/Body/f_upda_1.htm http://clhs.lisp.se/Body/f_upda_1.htm; you should get the gist even without knowing lisp. I'm overgeneralizing (I've had remote repls in production python application and used them to hotfix things), but only a little. You will appreciate the difference if you work with long running computations, where you don't want to have to start over from scratch if something went wrong right at the end.