My program is working fine but checkio shows Error

I would like to give some feedback about sort-by-extension.

Please find my answer from PyCharm in attachment. Checkio don't accept my code even if it's working proper.

From: https://py.checkio.org/mission/sort-by-extension/solve/

HTTP_USER_AGENT:

Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/81.0.4044.129 Safari/537.36

Source code: https://pastebin.com/ar90CKKN