From 31c2e9ec97581fedfbfb0e44e1756676abc938a1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?B=C3=A9n=C3=A9dikt=20Tran?=
 <10796600+picnixz@users.noreply.github.com>
Date: Mon, 13 Jan 2025 12:43:01 +0100
Subject: [PATCH 1/4] clear `StopAsyncIteration` before calling
 `_PyGen_SetStopIterationValue`

---
 Objects/genobject.c  | 1 +
 Objects/iterobject.c | 2 ++
 2 files changed, 3 insertions(+)

diff --git a/Objects/genobject.c b/Objects/genobject.c
index e87f199c2504ba..a4872de296e2cf 100644
--- a/Objects/genobject.c
+++ b/Objects/genobject.c
@@ -633,6 +633,7 @@ gen_iternext(PyObject *self)
 int
 _PyGen_SetStopIterationValue(PyObject *value)
 {
+    assert(!PyErr_Occurred());
     PyObject *e;
 
     if (value == NULL ||
diff --git a/Objects/iterobject.c b/Objects/iterobject.c
index 135ced9ea1f268..ebb342ff109222 100644
--- 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;

From 5db01cd3c20b6d73be8f76cba75b210c65f688b2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?B=C3=A9n=C3=A9dikt=20Tran?=
 <10796600+picnixz@users.noreply.github.com>
Date: Mon, 13 Jan 2025 12:48:39 +0100
Subject: [PATCH 2/4] blurb

---
 .../2025-01-13-12-48-30.gh-issue-128078.qOsl9B.rst              | 2 ++
 1 file changed, 2 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Core_and_Builtins/2025-01-13-12-48-30.gh-issue-128078.qOsl9B.rst

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
new file mode 100644
index 00000000000000..498864a0aa3145
--- /dev/null
+++ 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.

From e115e173255fd10889a1284312f3c17e6c99958f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?B=C3=A9n=C3=A9dikt=20Tran?=
 <10796600+picnixz@users.noreply.github.com>
Date: Mon, 13 Jan 2025 12:48:53 +0100
Subject: [PATCH 3/4] tests

---
 Lib/test/test_asyncgen.py | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/Lib/test/test_asyncgen.py b/Lib/test/test_asyncgen.py
index 5bfd789185c675..e9b741556ed0d5 100644
--- a/Lib/test/test_asyncgen.py
+++ b/Lib/test/test_asyncgen.py
@@ -1152,6 +1152,24 @@ 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__()
+            a, b = await anext(it, ('a', 'b'))
+            self.assertEqual(a, 'a')
+            self.assertEqual(b, 'b')
+
+        self.loop.run_until_complete(run())
+
     def test_async_gen_asyncio_anext_stopiteration(self):
         async def foo():
             try:

From 933324363a12bcdce6f58f2e5dc8b22ad7ea8bf3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?B=C3=A9n=C3=A9dikt=20Tran?=
 <10796600+picnixz@users.noreply.github.com>
Date: Mon, 13 Jan 2025 13:28:30 +0100
Subject: [PATCH 4/4] Update Lib/test/test_asyncgen.py

Co-authored-by: Kumar Aditya <kumaraditya@python.org>
---
 Lib/test/test_asyncgen.py | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/Lib/test/test_asyncgen.py b/Lib/test/test_asyncgen.py
index e9b741556ed0d5..3f631a03c9bf72 100644
--- a/Lib/test/test_asyncgen.py
+++ b/Lib/test/test_asyncgen.py
@@ -1164,9 +1164,8 @@ async def run():
             it = foo().__aiter__()
             with self.assertRaises(StopAsyncIteration):
                 await it.__anext__()
-            a, b = await anext(it, ('a', 'b'))
-            self.assertEqual(a, 'a')
-            self.assertEqual(b, 'b')
+            res = await anext(it, ('a', 'b'))
+            self.assertEqual(res, ('a', 'b'))
 
         self.loop.run_until_complete(run())