I think it's nicer when you want to wrap some execution path, and not just use it. If you could also provide the aforementioned pickled extra parameters, then this will be extremely useful.

The reason I'm reluctant is that you might have calls/functions/variables in global scope of the file storing the function, and then users will not know why something broke, ans it will be very cumbersome to debug.

The global scope for that function is the local scope of the current function. You could always pickle locals() (and warn regarding unpicklable parameters), or just warn that all used parameters must be passed explicitly (as arguments, or like in timeit.timeit(..., globals=...) ).