Does that only work in Python though? What about compiled languages? You don't really want to have to recompile your whole project again for every line you change...
mutmut right now is implemented by writing changes to disk and starting new processes. But you can implement it via "mutation schemata" where you functionally compile all possible mutants ahead of time, plus the original function, and replace the original function with a trampoline that either calls the original or one of the mutants depending on some external state.
I have a prototype of mutmut that does this and it's 10 to 100x faster. It does have the downside of not being able to mutate stuff like static global variables and such though.
