"Happy" may not be the most accurate choice of words () but we'll work with it.
A "happy" ball python is one that eats regularly and sleeps almost all the time. They'll typically sleep in their hides and the smaller and tighter the fit is, the "happier" they will be.
Refusal to eat and/or constantly cruising around its home are signs of a stressed (or "unhappy") snake. Some evening or nighttime activity is normal, but not constant or frequent movement. And some snakes it seems like you never see them move at all. That's normal, too.
While handling...if the snake cruises slowly and tongue-flicks and in general seems relaxed and ready to explore, those are all good signs. If they ball up tightly in your hands, strike out at you or the air, make jerky movements, or actively (franticly) try to escape your grasp...those are all signs that the ball python is stressed about being handled at that time and handling should be kept minimal.
Hope that has helped some!
Reply With Quote