FWIW, a Psyco-level JIT compiler can support reads from locals() or f_locals, but writes are harder.  The need to support writes would likely become another hard step on the way towards adding some simple JIT support to CPython in the future, should you decide you ever want to go that way.  (It is not a problem for PyPy but PyPy is not a simple JIT.)  Well, I guess CPython is not ever going down that path anyway.