technically, they are okay temporarily housed together, they will be stressed, but they will live... however,
I would never do what you are suggesting for the following reasons.
1) Quarantine: Your putting your own animal at risk by potentially exposing it to mites, and diseases which can be potentially life threatening. You should always quarantine for at least 3 months before introducing a new animal to your collection.
2) Unnecessary stress: Sometimes you can't avoid housing your animals together, however this should be very temporary and only under extreme circumstance. For example; I had my place fumigated as a precaution thanks to my neighbors :@ but I had to bring ALL of my ball pythons to a friends house. I had to fit 9 BP's in a 5 bin rack so unfortunately some of the girls got to share a bin for 24 hours. If your just looking to acquire a new pet, I don't consider that an extreme circumstance, or an emergency.
3) Inexperience: I don't want to be "that guy," but I am assuming that your a novice owner. Ball pythons are great pets for beginners because they are very easy to care for, and are quite forgiving.. However, you should do more research and learn as much as you can before deciding to bring more snakes into your collection. You should have things like basic husbandry memorized, as owning multiple reptiles takes a greater commitment and knowledge base. You run the risk of bringing contagions and ailments into the equation that you may not be equipped to handle.
I'm not trying to give you a hard time, or make you feel like I'm lecturing. But you should not bring another animal into that enclosure. It's not fair to either of the snakes.
Best of luck,
Chris.