gh-128078: Clear exception in anext before calling `_PyGen_SetStopI…

…terationValue` (GH-128780) (cherry picked from commit 76ffaef) Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com> Co-authored-by: Kumar Aditya <kumaraditya@python.org>
python · kumaraditya303 · Jan 13, 2025 · Jan 13, 2025 · Jan 13, 2025 · cfdefc9d91f25cd468f89d6185baee8f7186ac65
commit cfdefc9d91f25cd468f89d6185baee8f7186ac65
diff --git a/Lib/test/test_asyncgen.py b/Lib/test/test_asyncgen.py
@@ -1152,6 +1152,23 @@ async def run():
 
         self.loop.run_until_complete(run())
 
+    def test_async_gen_asyncio_anext_tuple_no_exceptions(self):
+        # StopAsyncIteration exceptions should be cleared.
+        # See: https://github.com/python/cpython/issues/128078.
+
+        async def foo():
+            if False:
+                yield (1, 2)
+
+        async def run():
+            it = foo().__aiter__()
+            with self.assertRaises(StopAsyncIteration):
+                await it.__anext__()
+            res = await anext(it, ('a', 'b'))
+            self.assertEqual(res, ('a', 'b'))
+
+        self.loop.run_until_complete(run())
+
     def test_async_gen_asyncio_anext_stopiteration(self):
         async def foo():
             try:

diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2025-01-13-12-48-30.gh-issue-128078.qOsl9B.rst b/Misc/NEWS.d/next/Core_and_Builtins/2025-01-13-12-48-30.gh-issue-128078.qOsl9B.rst
@@ -0,0 +1,2 @@
+Fix a :exc:`SystemError` when using :func:`anext` with a default tuple
+value. Patch by Bénédikt Tran.
@@ -604,6 +604,7 @@ gen_iternext(PyGenObject *gen)
 int
 _PyGen_SetStopIterationValue(PyObject *value)
 {
+    assert(!PyErr_Occurred());
     PyObject *e;
 
     if (value == NULL ||

diff --git a/Objects/iterobject.c b/Objects/iterobject.c
@@ -384,6 +384,7 @@ anextawaitable_iternext(anextawaitableobject *obj)
         return result;
     }
     if (PyErr_ExceptionMatches(PyExc_StopAsyncIteration)) {
+        PyErr_Clear();
         _PyGen_SetStopIterationValue(obj->default_value);
     }
     return NULL;
@@ -407,6 +408,7 @@ anextawaitable_proxy(anextawaitableobject *obj, char *meth, PyObject *arg) {
          * exception we replace it with a `StopIteration(default)`, as if
          * it was the return value of `__anext__()` coroutine.
          */
+        PyErr_Clear();
         _PyGen_SetStopIterationValue(obj->default_value);
     }
     return NULL;
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		Fix a :exc:`SystemError` when using :func:`anext` with a default tuple
		value. Patch by Bénédikt Tran.