After some further thought, I am open to changing the C API to accept either hi=None or hi=-1 to reconcile the implementation details without breaking any existing code that relies on either.  That would let the argument clinic expose a default value of hi=None.  That isn't perfect because it complicates the code and it exposes an implementation detail contrary to what the API originally intended.

Short of that, this module ought to be skipped for the argument clinic pending a build-out of signature objects to handle signatures that vary depending on the number of arguments supplied.