I really don't recommend doing that. Especially to a female.

If you know you want a small snake, and you really really want a ball python, adopt a small adult male who's a few years old already. That way you know how big he's going to be.

Be prepared for the snake to stop eating entirely in the winter, and then become aggressively hungry in the summer. Ball python appetites vary with the season. Please don't starve a hungry ball python in the summer. They need to build up fat reservoirs for the winter.

...or you can just buy a corn snake, or a children's python. There are plenty of really awesome snakes that only get to 3 ft.