Georg noted that the PEP 380 patch added a couple of new C interfaces without documenting them. These interfaces need to be either:
1. Documented;
2. Made private; or
3. Removed (if they're completely trivial)

PyGen_FetchStopIterationValue: probably document, explicitly noting that it also clears the StopIteration exception from the thread state

PyStopIteration_Create: probably remove

The current use of PyStopIteration_Create in genobject.c can probably be replaced with PyErr_SetObject(PyExc_StopIteration, value) anyway.

Also check any GetAttr and CallMethod operations to see if they should be moved over to the new *Id variants.

'PyStopIteration_Create' is just a trivial wrapper:

PyObject *
PyStopIteration_Create(PyObject *value)
{
    return PyObject_CallFunctionObjArgs(PyExc_StopIteration, value, NULL);
}

It is not needed.

As for 'PyGen_FetchStopIterationValue', does it really need to be public?  It is trivial to make it private because all calls to it are in 'genobject.c'.  However, I am not sure if there is a strong use case for having it public.

There is one call to PyGen_FetchStopIterationValue in ceval.c.

But I don't think it should be public. 

There is no real reason for the "Gen" in the name. The function is used by generator handling code, but the code itself relates to StopIteration.
Perhaps it should be moved to errors.c and renamed _PyErr_FetchStopIterationValue.

New changeset cfbf6aa5c9e3 by Nick Coghlan in branch 'default':
Issue #13783: the PEP 380 implementation no longer expands the public C API
http://hg.python.org/cpython/rev/cfbf6aa5c9e3

New changeset 438b861e2edb by Nick Coghlan in branch 'default':
Issue #13783: PEP 380 cleanup part 2, using the new identifier APIs in the generator implementation
http://hg.python.org/cpython/rev/438b861e2edb

I left the name of the new private API as _PyGen_FetchStopIterationValue. If anyone wants to make it public, they can raise a new issue to give it a more appropriate name (and move the definition accordingly).

PyStopIteration_Create is simply gone, replaced by the underlying call.