Unless you had a massive display enclosure, like the zoos have, with ALOT OF VENTILATION I would personally leave them in seperate enclosures. I worked in a zoo that had a display with a coastal carpet python above a turtle pond with mary rivers and some fish in it. It didn't seem like the best idea to me. The snake got scale-rot from a too high humidity created by the large body of water and needed heat, which in itself is enough to repel me from that idea. The turtles never came out to bask. There didn't seem to be enough UV reaching them also, due to the massive size of the enclosure, and the turtles ended up needing treatment for shell rot. (Minor case of it, however still a big turn-off for the enclosure idea).
Both turtles and pythons need a very different enclosure setup for both to have optimum health, which they would get if housed seperately. Also, turtles are alot of work to keep, they spoil thier water very quickly and if housed with a snake I could see the cleaning process to be very vigorous and not worth it. Personally, I would not do it.