Once you see ribs there's no return unless you force feed. But from what it sounds like, you got a ball python lol. We all get frustrated with our balls, ball pythons that is lol. Now try feeding him every two weeks instead of every week. Balls can go for more then 3 months without eating that's if they are at a nice weight to begin with which yours sounded like it did. In the wild they eat 12 meals a year if there lucky, which means one meal a month. Crazy but true.