pyotp2289 is a pure Python 3 implementation of RFC-2289 -
"A One-Time Password System"

"The system provides authentication for system access (login) and other
applications requiring authentication that is secure against passive attacks
based on replaying captured reusable passwords. OTP evolved from the S/KEY
(S/KEY is a trademark of Bellcore) One-Time Password System that was released
by Bellcore."