gh-104050: Add basic typing to CConverter in clinic.py by erlend-aasland · Pull Request #104538 · python/cpython

Doesn't need to be done now (and you may not like the suggestion), but you could use an enum for all the sentinels that are defined in clinic.py, instead of defining three separate classes (Unspecified, Null and Unknown):

import enum
from typing import Final

class Sentinels(enum.Enum):
    unspecified = 'Unspecified'
    NULL = 'Null'
    unknown = 'Unknown'

    def __repr__(self):
        return f'<{self.value}>'


unspecified: Final = Sentinels.unspecified
NULL: Final = Sentinels.NULL
unknown: Final = Sentinels.unknown

If you did that, then you'd be able to use a typing.Literal annotation here, which would be more expressive of the fact that unspecified is a singleton: