> _PyObject_FastCallKeywords(PyObject **args, int nargs, PyObject **kwargs, int nkwargs): nkwargs is the number of (key, value) pairs

Hum, I don't know if it's worth to "split" the C array into two parts. Maybe it can be just:

_PyObject_FastCallKeywords(PyObject **args, int nargs, int nkwargs);

As current used in Python/ceval.c.