bpo-31861: Add aiter and anext to builtins (#23847)

Co-authored-by: jab <jab@users.noreply.github.com>
Co-authored-by: Daniel Pope <mauve@mauveweb.co.uk>
Co-authored-by: Justin Wang <justin39@gmail.com>
diff --git a/Python/clinic/bltinmodule.c.h b/Python/clinic/bltinmodule.c.h
index bc3b518..545f5b5 100644
--- a/Python/clinic/bltinmodule.c.h
+++ b/Python/clinic/bltinmodule.c.h
@@ -530,6 +530,50 @@ PyDoc_STRVAR(builtin_hex__doc__,
 #define BUILTIN_HEX_METHODDEF    \
     {"hex", (PyCFunction)builtin_hex, METH_O, builtin_hex__doc__},
 
+PyDoc_STRVAR(builtin_aiter__doc__,
+"aiter($module, async_iterable, /)\n"
+"--\n"
+"\n"
+"Return an AsyncIterator for an AsyncIterable object.");
+
+#define BUILTIN_AITER_METHODDEF    \
+    {"aiter", (PyCFunction)builtin_aiter, METH_O, builtin_aiter__doc__},
+
+PyDoc_STRVAR(builtin_anext__doc__,
+"anext($module, aiterator, default=<unrepresentable>, /)\n"
+"--\n"
+"\n"
+"Return the next item from the async iterator.");
+
+#define BUILTIN_ANEXT_METHODDEF    \
+    {"anext", (PyCFunction)(void(*)(void))builtin_anext, METH_FASTCALL, builtin_anext__doc__},
+
+static PyObject *
+builtin_anext_impl(PyObject *module, PyObject *aiterator,
+                   PyObject *default_value);
+
+static PyObject *
+builtin_anext(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
+{
+    PyObject *return_value = NULL;
+    PyObject *aiterator;
+    PyObject *default_value = NULL;
+
+    if (!_PyArg_CheckPositional("anext", nargs, 1, 2)) {
+        goto exit;
+    }
+    aiterator = args[0];
+    if (nargs < 2) {
+        goto skip_optional;
+    }
+    default_value = args[1];
+skip_optional:
+    return_value = builtin_anext_impl(module, aiterator, default_value);
+
+exit:
+    return return_value;
+}
+
 PyDoc_STRVAR(builtin_len__doc__,
 "len($module, obj, /)\n"
 "--\n"
@@ -830,4 +874,4 @@ builtin_issubclass(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=e2fcf0201790367c input=a9049054013a1b77]*/
+/*[clinic end generated code: output=da9ae459e9233259 input=a9049054013a1b77]*/