Judy pretty much covered it, but if you're already keeping rats, there's not much reason not to breed non-fancy rats to feed a ball python. When the ball is little, you can alternate between rat pinks and adult mice to make sure that he's getting enough protein and calcium and that he's willing to take rats. Then when he's big enough to eat rat hoppers, you can drop the mice altogether. My kids each have a pet rat and we haven't had any problems with that, but I do make sure that their hands are washed thoroughly between handling one and the other.