[3.12] gh-128078: Clear exception in anext before calling _PyGen_SetStopIterationValue (GH-128780) (#128784)

miss-islington · picnixz · kumaraditya303 · web-flow · commit 4facd7d119a6 · 2025-01-13T18:45:20.000+05:30
gh-128078: Clear exception in `anext` before calling `_PyGen_SetStopIterationValue` (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>
diff --git a/Lib/test/test_asyncgen.py b/Lib/test/test_asyncgen.py
@@ -1100,6 +1100,23 @@ 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.
diff --git a/Objects/genobject.c b/Objects/genobject.c
@@ -618,6 +618,7 @@ 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
@@ -382,6 +382,7 @@ anextawaitable_iternext(anextawaitableobject *obj)
         return result;
     }
     if (PyErr_ExceptionMatches(PyExc_StopAsyncIteration)) {
+        PyErr_Clear();
         _PyGen_SetStopIterationValue(obj->default_value);
     }
     return NULL;
@@ -405,6 +406,7 @@ 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 @@`
	`1`	+Fix a :exc:`SystemError` when using :func:`anext` with a default tuple
	`2`	`+value. Patch by Bénédikt Tran.`
Original file line number	Diff line number	Diff line change
`@@ -618,6 +618,7 @@ gen_iternext(PyGenObject *gen)`
`618`	`618`	`int`
`619`	`619`	`_PyGen_SetStopIterationValue(PyObject *value)`
`620`	`620`	`{`
	`621`	`+ assert(!PyErr_Occurred());`
`621`	`622`	`PyObject *e;`
`622`	`623`
`623`	`624`	`if (value == NULL \|\|`
Original file line number	Diff line number	Diff line change
`@@ -382,6 +382,7 @@ anextawaitable_iternext(anextawaitableobject *obj)`
`382`	`382`	`return result;`
`383`	`383`	`}`
`384`	`384`	`if (PyErr_ExceptionMatches(PyExc_StopAsyncIteration)) {`
	`385`	`+ PyErr_Clear();`
`385`	`386`	`_PyGen_SetStopIterationValue(obj->default_value);`
`386`	`387`	`}`
`387`	`388`	`return NULL;`
`@@ -405,6 +406,7 @@ anextawaitable_proxy(anextawaitableobject obj, char meth, PyObject *arg) {`
`405`	`406`	* exception we replace it with a `StopIteration(default)`, as if
`406`	`407`	* it was the return value of `__anext__()` coroutine.
`407`	`408`	`*/`
	`409`	`+ PyErr_Clear();`
`408`	`410`	`_PyGen_SetStopIterationValue(obj->default_value);`
`409`	`411`	`}`
`410`	`412`	`return NULL;`