bpo-37194: Add a new public PyObject_CallNoArgs() function (GH-13890)

Add a new public PyObject_CallNoArgs() function to the C API: call a
callable Python object without any arguments.

It is the most efficient way to call a callback without any argument.
On x86-64, for example, PyObject_CallFunctionObjArgs(func, NULL)
allocates 960 bytes on the stack per call, whereas
PyObject_CallNoArgs(func) only allocates 624 bytes per call.

It is excluded from stable ABI 3.8.

Replace private _PyObject_CallNoArg() with public
PyObject_CallNoArgs() in C extensions: _asyncio, _datetime,
_elementtree, _pickle, _tkinter and readline.

1 files changed, 3 insertions, 1 deletions

diff --git a/Include/cpython/abstract.h b/Include/cpython/abstract.h
index d036912..415f3e1 100644
--- a/Include/cpython/abstract.h
+++ b/Include/cpython/abstract.h
@@ -144,7 +144,9 @@ _PyObject_FastCall(PyObject *func, PyObject *const *args, Py_ssize_t nargs)
     return _PyObject_Vectorcall(func, args, (size_t)nargs, NULL);
 }
 
-/* Call a callable without any arguments */
+/* Call a callable without any arguments
+   Private static inline function variant of public function
+   PyObject_CallNoArgs(). */
 static inline PyObject *
 _PyObject_CallNoArg(PyObject *func) {
     return _PyObject_Vectorcall(func, NULL, 0, NULL);