You should read this thread, it is a lot of back and forth and shows just how debated that subject is.
http://www.ball-pythons.net/forums/s...ad.php?t=61251

And it all starts at page 3

For a beginner to keeping ball pythons, I think a 4 x 2 x 2 is too large and hard to maintain proper climate control and cleanliness while offering too little chances of being able to accurately identify when the snake(s) are ill or in need.

One snake in one cage.