Also, a lot of times the ball pythons in the same enclosure at the pet store, even if all males, are still babies. Males will not fight each other until sexual maturity, surely the 3 1/2 foot python you just inerited is an adult and is guaranteed to fight with your current male.
And as previously said (quite wonderfully might I add) NEVER EVER house bps together, and all new snakes must be quarantined for some time before being in contact with other bps.