Hi and welcome!
I have kept snakes and rats in the same house for several years now and I have never had any problems. When I was back at home and only had one room (my bedroom) to keep my animals in, I still was able to keep them separate enough so as not to cause stress to either animal. For one thing, I completely emptied my closet and kept the rat cage in there. I left the doors open almost all the time, but I could close them when handling or feeding my reptiles. Like jo said, this would stress out your rats, but it would also stress out your snake (and depending on the species, you would be putting your rats in danger if you were, say, holding your snake right next to the rat cage. However, since your talking about a Ball Python this wouldn't likely be a problem) And, since we are talking about a Ball Python, even a little bit of stress could trigger it to go off feed, which would not be good.
However, if you can give them more room apart that would be even better. There are just a few things to remember when you own both reptiles and rats: Never handle or attempt to play with your rats right after your snake. You should at least wash you hands, to get the smell off of you, otherwise you will stress them out and they may even bite you, thinking that you are a snake. Same goes the other way around. Never handle or play with your snake right after handling you rats for the same reasons as above. Ideally, if you change your clothes between the two (and maybe have a shower) that would be great, but at very least wash your hands (which you should do before and after handling any animal anyway, but especially in this situation)
People always seem surprised when they find out I own both of these amazing animals, and if you get them both be prepared for the same questions to be asked over and over and over again lol. In the end though, it doesn't really matter because you get the best of both worlds. There aren't many of us in the middle, but it's OK because we have the privilege of caring for not one, but two amazing types of animal :thumbup:
? Owning snakes, or both in the same house?