I found this on a website
Re: How can you tell the difference between a male and female python?
Thanks for asking a good question. Most people cannot tell just by looking
at a python whether it is male or female. In some species of pythons, for
example, the Black Headed Python, whose scientific name is Aspidites
melanocephalus, the female is larger than the male. Other species are more difficult to tell apart.
There are two ways to find out for sure if a snake is male or female.
The males have a pair of HEMIPENES hidden underneath scales on their
bellies. With young snakes, an expert snake handler can gently put
pressure on the right spot and pop the hemipenes out through the cloaca. Only the male snakes have hemipenes, the females do not.
Another way is called PROBING. A steel probe, like a large dull needle,
can be inserted in the cloaca and pushed under the tail of the snake.
The distance the probe goes in tells you if the snake is male or female.
The probe goes further in male snakes.
BOTH OF THESE TESTS SHOULD ONLY BE ATTEMPTED BY AN EXPERT TO AVOID
INJURING OR FRIGHTENING THE SNAKE.
I was told and show how to pop my snakes by my vet thats how i sexed all mine and a pet shop.
Snakes are very interesting animals, and if you would like to learn
more, you can check out a whole website about pythons at
Harford Reptile Breeding Center - Specializing in Rare Pythons & Leopard Geckos
Hope this helps you Sam