A Python sounds like a great thing for any fish keeper to have so that you don't have to lug around heavy buckets of water and waste time when emptying/refilling!

Is there anything I should know before I get one?

Do you need to leave the facet water running while you are emptying water from your tank? That part I don't understand?

The part about leaving the facet on - I have a python and I just put one end of my python in the tank and the other end out a window so I can use the water to water plants and the lawn. I hate wasting water like that. You may have no choice though if you don't have any windows or doors nearby.