Define _PyCFunctionFastWithKeywords() on CPython 3.7+

[ijl]

https://docs.python.org/3/c-api/structures.html#c._PyCFunctionFastWithKeywords

[ijl]

Regarding the 3.7 cfg, this was introduced in cpython commit 6969eaf4682beb01bc95eeb14f5ce6c01312e297 and first tagged in v3.7.0a1.

[davidhewitt]

Thanks for this!

I've got a tiny nit on the changelog and this is good to merge. Looking at the docs you linked I noticed there's a couple of other mismatches we have:

• we incorrectly use args: *mut *mut PyObject in _PyCFunctionFast when it should also be *const *mut PyObject like you have used here.
• we're also missing PyCMethod for Python 3.9 and up.

This PR is good to merge with the suggested changelog entry. However, if you've got a moment and willing to fix the above points at the same time I'd be very grateful! 👍

[nw0]

we incorrectly use args: *mut *mut PyObject in _PyCFunctionFast when it should also be *const *mut PyObject like you have used here.

This is actually correct for 3.6:

typedef PyObject *(*_PyCFunctionFast) (PyObject *self, PyObject **args,
                                       Py_ssize_t nargs, PyObject *kwnames);

[davidhewitt]

👍 thanks for the review @nw0 - in which case I'll merge this now and we can leave further corrections for #1289

[ijl]

I see you committed the rewording, thanks.