Aside from differences in length, there are no other external markers that reliably discern between male and female ball pythons. The most widely accepted methods of ball python sexing are known as “popping” and “probing.”
Popping is a procedure which, when performed correctly, opens the snake’s vent and exposes hemipenes (if present). “Popping” is most safely done on young snakes, and despite the how-to videos on YouTube, should never be attempted by an amateur. Let your vet or a breeder do it for you.
Probing uses a slender metal rod to determine a snake’s sex based on the placement and size of its reproductive organs. If the rod inserts only a short distance into the vent (toward the tail), the snake is female. If the rod goes further, it’s male (the extra distance suggests the presence of hemipenes). Probing is the preferred method of sexing for adult snakes. Like popping, probing should not be attempted by amateurs, and is best performed by a certified reptile veterinarian or ball python breeder.