functions with keyword-only arguments have this form:
    def f(x, *args, y):
        pass
parameters can appear after the *arg, they are required to be passed by
keyword.

It would be more consistent to allow this function call:
    f(X, *ARGS, y=Y)
This is invalid syntax, *ARGS is required to be at the end of the
arguments, together with an eventual **KWARGS. This restriction should
be lifted.

See the use case in
http://mail.python.org/pipermail/python-3000/2008-July/014437.html