Actually the screen on an aquarium will work against you as far as keeping heat an humidity at appropriate levels, it all just escapes through the top. The aquarium would be more for you than for your ball python.

With tubs or PVC cages (Animal Plastics, Boaphiles...) you usually use a UTH attached to a thermostat. Humidity levels can be controlled by what substrate you use, how big the water dish is, and where you place the water dish. The snake also feels more secure in its "box" than it would in a fish tank, even a fish tank with lots of hides.