I'm pretty sure all snakes only eat dead, or at least paralysed prey. The non-venomous snakes [pythons, carpet snakes and boas etc.] also have pre-digestive enzymes in the esophagus similar to that found in the venomous ones, which would soon disable any prey that may still have some live in it, if they went to devour them before the life was constricted out of it.
There are non-venomous snakes that will eat venomous snakes. The digestive juices in the stomach neutralises any toxin that is contained in venomous animals they eat.