Keeping a ball python in a 125 gallon enclosure would be fine. As long as the husbandry is met and the tank is "busy" with decorations, the bp will be fine. But dont have two hides a water bowl and newspaper substrate and thats it. Your snake will stress. In the wild they have plenty of holes and burrows to get in when they need to and its not just barren, there is grass, some trees and shrubbery.

These snakes that we keep as pets are NOT in the wild
Yes they are pets, but not domesticated by any means. We could put them in the wild and they would know what to do. Our herps instinctevly know what to do when it comes to surviving. As much as we like to think they love us and come out to see us, its just not true. They are acting on instinct, always, with limited cognitive thought. Yes some snakes such as retics will get into a routine with their owners and recognize them over a stranger, but with any herp we own, bringing them to the wild, they would know what to do. So if you set it up as a naturalist setup, with driftwood/branches, plenty of leaves for ground cover, around four hides, and a large water dish, the BP will do just fine. I am assuming that the temps are consistant with correct husbandry and the humidity is kept at appropriate levels.