I understand that letting any anonymous user upload any sort of file in general can be dangerous, especially if it's code. However, I have an idea to let users upload custom AI scripts to my website. I would provide the template so that the user could compete with other AI's in an online web game I wrote in Python. I either need a solution to ensure a user couldn't compromise any other files or inject malicious code via their uploaded script or a solution for client-side execution of the game. Any suggestions? (I'm looking for a solution that will work with my Python scripts)
Have an extensive API for the users and strip all other calls upon upload (such as import statements).  Also, strip everything that has anything to do with file i/o.
(You might want to do multiple passes to ensure that you didn't miss anything.)
Letting users upload Python scripts for execution