Some functions in cpython are private. These APIs are called from only python executable or DLL. They are not called even from extension modules in stdlib.
In this time, I want to keep _PyObject_GetMethod private. https://github.com/python/cpython/pull/14015#discussion_r293351734
As far as I know, it is used to expose the function from DLL user on Windows. So I think when the private function is not intended to be called from outside of DLL, it should not use PyAPI_FUNC. Am I collect?
Currently, many private APIs uses `PyAPI_FUNC()`. Is there any downside about having much unnecessary exported functions? (e.g. slower calling invention is used, bothering link time optimization, LoadLibrary get slower, etc...)