Unnecessary precaution.
If you're getting in and out of the tank for other reasons (even just to spot-clean and change water, but especially if you're handling it as you would any pet), the snake isn't going to associate every opening of the enclosure with feeding.
The only reason you would feed a snake in a separate enclosure would be to prevent substrate ingestion and as a personal preference thing--some people like to be able to do a health check and get a weight on the snake right before feeding. (Others do this other times of the week; you're checking its health every time you handle it and you don't have to weigh a snake right before it eats.)
With ball pythons, definitely, feeding in a separate enclosure is overrated and extremely unnecessary. In fact, it's possibly detrimental. Ball pythons tend to be picky feeders, and are easily knocked off feeding. The slightest excess stress can trigger a feeding strike, and being transferred to a separate, unfamiliar, and stark empty (no hides) tub for feeding is definitely a stressful situation. Though your average corn snake or other, more hardy species can get over that with ease, ball pythons are infamous for taking a small move like that and turning it into a 6-month feeding strike.
It's best to avoid unnecessary stress and feed the snake in its enclosure. If you're worried about substrate ingestion, that's easily solved by placing the prey on a plate, out of the substrate, or at least drying it off so substrate won't stick to its surface. If you're worried about your snake being "mean," well... Aside from that being largely a myth, your normal activities in and out of the tank the rest of the week (and some common sense--i.e. wash your hands after touching rats and mice) will prevent any or most cases of mistaken identity.
On another note... Since the previous post mentioned live-feeding, let me say that that is NOT NECESSARY. You can feed a snake pre-killed prey. You can purchase frozen rats and mice that are just as nutritious and even safer (won't bite back, won't transfer parasites) than live prey that you can simply thaw out in water (hence the comment of drying the prey earlier) prior to feeding. Some snakes refuse to take anything but live prey, but even that is extremely rare. The previous poster's feeding live is strictly their own decision, as I highly doubt their snake can't be switched to f/t (or that the person has tried especially hard, if at all). The best thing for your animal's safety is to feed frozen/thaw or at least pre-killed prey... There have been far too many cases of snakes being bitten, and even eaten alive, by their rodent prey. Even supervised live feeding isn't safe, as a mouse can bite a LOT faster than you can reach in and stop it.
Good luck with your ball! They can be great pets.