I have never had the problem with a Ball Python to turn nasty at least not me but I did have a burmese that did the same thing except she
was about 8 feet when I got her back. Anyway in her case I put her on a regular feeding schedule and started handling her with gloves at first once she was used to having food again.
Than after a while she came around and I could handle her like I used too.
Anyway she is still nice and in a good home now since I moved away from Burmese all together.
My suggestion is give it time and work with him I think he will come around.