Check your outer for loop - range(len(s))?
If s is of length 1, the for loop does not execute.
You probably need range(len(s)+1)?

I had the same problem. It means that the function is not running the "correct" number of times. I had to change my original working code to accomodate the checking program. What I thought/think is the best solution doesn't run the exact number of times that is expected by the program.

Please can you post Kata-specific problems on the discourse page for that Kata instead of the forum which is for general topics. Each Kata has an automatic discourse page in which you can mark your comment as a question, which means it's easier for me to help (since it's easier to find). Also, since this is a forum page, I can't mark your comment as a spoiler, meaning people can look at your code and use it themselves, however on the discourse page I can hide your solution.

Somebody already answered your question on your other comment so I won't comment about that here.

because split is used in string objects (str) not list objects.