"To explicitly declare that a certain class implements a given protocol, it can be used as a regular base class. In this case a class could use default implementations of protocol members. Static analysis tools are expected to automatically detect that a class implements a given protocol. So while it’s possible to subclass a protocol explicitly, it’s not necessary to do so for the sake of type-checking."

https://peps.python.org/pep-0544/#explicitly-declaring-imple...