Yes you can cheat if you use your own memoizer too, if you "know" what your function does. Mine f'rinstance memoizes data fetched over the network even tho' as a function that is wildly impure, it can either age it out or check the last modification time. So I have one decorator for pure computations performed locally and impure performed remotely. Obviously this can only be done if the same person/team is maintaining both or it'll all go horribly wrong...