bpo-37165: Convert _count_elements to the argument clinic (GH-13848)

(cherry picked from commit e985804)

Co-authored-by: Raymond Hettinger <rhettinger@users.noreply.github.com>

Misc/NEWS.d/next/Library/2019-06-05-11-48-19.bpo-37165.V_rwfE.rst

@@ -0,0 +1 @@
+Converted _collections._count_elements to use the Argument Clinic.

Modules/_collectionsmodule.c

@@ -8,9 +8,10 @@
 #endif
 
 /*[clinic input]
+module _collections
 class _tuplegetter "_tuplegetterobject *" "&tuplegetter_type"
 [clinic start generated code]*/
-/*[clinic end generated code: output=da39a3ee5e6b4b0d input=ee5ed5baabe35068]*/
+/*[clinic end generated code: output=da39a3ee5e6b4b0d input=a8ece4ccad7e30ac]*/
 
 static PyTypeObject tuplegetter_type;
 #include "clinic/_collectionsmodule.c.h"
@@ -2228,17 +2229,24 @@ static PyTypeObject defdict_type = {
 
 /* helper function for Counter  *********************************************/
 
-PyDoc_STRVAR(_count_elements_doc,
-"_count_elements(mapping, iterable) -> None\n\
-\n\
-Count elements in the iterable, updating the mapping");
+/*[clinic input]
+_collections._count_elements
+
+    mapping: object
+    iterable: object
+    /
+
+Count elements in the iterable, updating the mapping
+[clinic start generated code]*/
 
 static PyObject *
-_count_elements(PyObject *self, PyObject *args)
+_collections__count_elements_impl(PyObject *module, PyObject *mapping,
+                                  PyObject *iterable)
+/*[clinic end generated code: output=7e0c1789636b3d8f input=e79fad04534a0b45]*/
 {
     _Py_IDENTIFIER(get);
     _Py_IDENTIFIER(__setitem__);
-    PyObject *it, *iterable, *mapping, *oldval;
+    PyObject *it, *oldval;
     PyObject *newval = NULL;
     PyObject *key = NULL;
     PyObject *bound_get = NULL;
@@ -2247,9 +2255,6 @@ _count_elements(PyObject *self, PyObject *args)
     PyObject *mapping_setitem;
     PyObject *dict_setitem;
 
-    if (!PyArg_UnpackTuple(args, "_count_elements", 2, 2, &mapping, &iterable))
-        return NULL;
-
     it = PyObject_GetIter(iterable);
     if (it == NULL)
         return NULL;
@@ -2510,7 +2515,7 @@ PyDoc_STRVAR(module_doc,
 ");
 
 static struct PyMethodDef module_functions[] = {
-    {"_count_elements", _count_elements,    METH_VARARGS,   _count_elements_doc},
+    _COLLECTIONS__COUNT_ELEMENTS_METHODDEF
     {NULL,       NULL}          /* sentinel */
 };