A heat lamp is not the way to go. It dries out the air and will make it harder for your ball python to shed. Get an under tank heater and some kind of temp controll. The under tank heaters can spike up to 115 degrees and burn them.
Look on Big Apples web site to give you an idea of what your looking for and cost. They have some of the lower end stuff that works just find that wont burn giant holes in your wallet.
http://www.bigappleherp.com/REPTILE-...4Pa38Ta38Pc3j0