gh-154791: Fix asyncio Future losing traceback on repeated result() calls

Author: iaroslavkrasikov

Lib/test/test_asyncio/test_futures2.py

@@ -28,6 +28,26 @@ async def raise_exc():
             else:
                 self.fail('TypeError was not raised')
 
+    async def test_future_traceback_preserved_after_suppress(self):
+        async def raise_exc():
+            raise TypeError(42)
+
+        future = self.cls(raise_exc())
+        try:
+            await future
+        except TypeError:
+            pass
+
+        try:
+            await future
+        except TypeError as e:
+            tb = ''.join(traceback.format_tb(e.__traceback__))
+            self.assertIn('raise_exc', tb,
+                'Original raise site lost after first result() call')
+        else:
+            self.fail('TypeError was not raised')
+
+
     async def test_task_exc_handler_correct_context(self):
         # see https://github.com/python/cpython/issues/96704
         name = contextvars.ContextVar('name', default='foo')

Misc/NEWS.d/next/Library/2026-07-28-08-02-41.gh-issue-154791.ey7POa.rst

@@ -0,0 +1,4 @@
+Fix `asyncio._CFuture` losing the initial exception traceback frames when
+`Future.result()` is called more than once. Previously, the C implementation
+cleared the stored traceback after the first call, causing subsequent raises
+to omit the original raise site. The Python implementation was unaffected.

Modules/_asynciomodule.c

@@ -769,7 +769,6 @@ future_get_result(asyncio_state *state, FutureObj *fut, PyObject **result)
             return -1;
         }
         *result = Py_NewRef(fut->fut_exception);
-        Py_CLEAR(fut->fut_exception_tb);
         return 1;
     }