> I would suggest to use sys.maxsize for default value in Argument Clinic

No thanks.  I don't want to subtly change the API for this module or even suggest to users that it might be a good idea to set hi > len.  Further, we don't want to slow the pure python code for this pointless extension.

Really, we're dancing around the issue that argument clinic and signatures need to become more expressive, allowing for omitted arguments without requiring a default value.  Waiting for this to be done is far preferable to mangling long-standing APIs to force fit them to into argument clinic.

Elsewhere, we've shown self discipline and restraint when applying AC, skipping over cases where it doesn't fit.  If we can't find a way to apply AC without changing this API, this issue should be closed and deferred until AC grows the requisite expressive power.