I've been using emacs for a few months now (it's surprisingly good), and am starting to run into wanting to do little modifications. Speaking as a non-lisper, I really wish a rewrite existed in a more modern language. I don't wanna start an argument about lisp here but there is a reason people don't use it for major developments, and it's not the performance. But it would be unfair not to point out that you can extend emacs in a variety of languages including python. Its just a bit messier.