Backup your code, click Reset, paste it and try again. Also, make sure your function's name is rps.

There is an error in the python language in the tests:

"Traceback (most recent call last):
File "/workspace/default/tests.py", line 2, in
from solution import rps
ImportError: cannot import name 'rps' from 'solution' (/workspace/default/solution.py)"

There is a flaw in your code, it doesn't reduce duplicates correctly. See the error message for test 'AA':

should reduce duplicates
Log
[] should equal ['A']

note: 53,566 solves in Python