I got a ball python a while back that was vicious. He was also dehydrated and very hungry. After he got his fill of water and rats and a couple of weeks to settle in he was still not crazy about being picked up, but he wasn't biting.

A snake that is stressed out by hunger, thirst, or unfamiliar surroundings tends to snap at a hand reaching toward it. Picking the snake up from the outer part of the coil (not the neck) behind the head is less threatening to them. I've used a snake hook on smaller biters and that seems to work because they're not as threatened by the hand if they're placed in it. With a larger snake sometimes touching the top of the head with the hook will make them coil and then they can be lifted from the back of the coil.

Your snake is probably still not used to his new surroundings. You might want to give him another week or so before you handle him.

I don't pay much attention to hissers if they aren't striking. Two of mine do that and they handle fine. One of them will hiss back at me if I hiss at him. Yeah, now if that isn't a spectacle ...