Help me identify it's gender: male of female?

[The Serpent Merchant]

There's no way to tell based on tail length. The only way to know for sure whether it's male or female is to have it probed by someone who knows what they're doing.

x2, you can either "Probe" a ball python, or "Pop" them. both methods are difficult until you get the hang of it, and if done incorrectly can hurt/damage your snake.