Lots of keepers underestimate the dangers of keeping and handling large constrictors, especially the big six. We think that because they're not venomous and often very tractable and easy to handle (except for their weight which can often get to 100kg +) that they are not especially dangerous. A big constrictor, however, can deliver a very damaging bite and wrap and drop the careless keeper in an instant, and if that keeper is alone, he will die before he can call for help, whereas if bitten by a ven, the keeper usually has time to call for help and can take steps to minimise the damage caused by envenomation.
When handling any constrictor (python) over around 3m, you should always have someone else around to assist if things literally get out of hand. We always become complacent about safety with animals which are usually docile, but factors of which we may be unaware can change animal behaviour very quickly.
Jamie