I don't know how this myth keeps getting perpetuated. There is a small bit of truth in that if you feed them more when younger that they will get a bit bigger as adults, but the concept that you can control your animal's size by starving them and keeping them in a small enclosure is just wrong. If you want a happy and healthy ball python you should keep it in an appropriately sized enclosure (not too small or too big) with hides, proper humidy, clean substrate, heat gradient and feed it an appropriately sized food item once a week or so as it's growing. When it's full grown it won't need to be fed quite as often, but once a month is still too long IMHO.