and you are right judy. the snake would have to be neglected to create that association between hand=food because the only interaction it would have with the hand would be water change and feeding(no tank cleaning because that involves handling)...
not recommended but possible.
i know a guy whos kids have a beardie that keeps biting the kids cuz the beardie associated their hands with food. they clean the poop, feed him, give him greens, but i guess when the novelty of owning a lizard wore off they stopped holding him and thats how it happend.