3.8.2 (on Alpine Linux under WSL) produces '0020-10-05', just like your 3.6 example. Not seeing anything obvious in commit history that would break it for 3.7. That said, 3.7 is in security fix only mode at this point (see https://devguide.python.org/#status-of-python-branches ); as this works on the latest release, I'm thinking this won't be fixed for 3.7.