How can I automatically add someone’s following to a Twitter List

I want to create a Twitter list that consists of all of a users “following”. Not followers, but the users that user is following. There are roughly 2k accounts I want to add to that list. Because of this, I want to be able to do this automatically.

I have some experience with APIs through Python and would be willing to learn to write a script for this if possible. If it is possible, please recommend some libraries that could be of use.