gh-159401: Suppress duplicate task warnings for reraised BaseExceptions

Lib/asyncio/tasks.py

@@ -313,6 +313,10 @@ def __step_run_and_handle_result(self, exc):
             super().cancel()  # I.e., Future.cancel(self).
         except (KeyboardInterrupt, SystemExit) as exc:
             super().set_exception(exc)
+            # This exception is re-raised to the event loop instead of being
+            # retained solely by this Task, so it is not unhandled if the
+            # task cannot subsequently be awaited during loop shutdown.
+            self._log_traceback = False
             raise
         except BaseException as exc:
             super().set_exception(exc)

Lib/test/test_asyncio/test_tasks.py

@@ -1965,6 +1965,17 @@ async def current_task(exc):
                 self.assertTrue(not t.cancelled())
                 self.assertEqual(t.result(), "ok")
 
+    def test_step_does_not_log_reraised_base_exceptions(self):
+        async def raise_exception(exc):
+            raise exc
+
+        for exc_type in (SystemExit, KeyboardInterrupt):
+            with self.subTest(exc_type=exc_type):
+                task = self.new_task(self.loop, raise_exception(exc_type()))
+                with self.assertRaises(exc_type):
+                    self.loop.run_until_complete(task)
+                self.assertFalse(task._log_traceback)
+
     def test_step_result_future(self):
         # If coroutine returns future, task waits on this future.
 

Misc/NEWS.d/next/Library/2026-10-14-10-59-00.gh-issue-159401.c17QdV.rst

@@ -0,0 +1,3 @@
+Suppress a duplicate ``Task exception was never retrieved`` warning when an
+asyncio task raises :exc:`SystemExit` or :exc:`KeyboardInterrupt`, which is
+already propagated by the event loop.

Modules/_asynciomodule.c

@@ -3129,7 +3129,10 @@ task_step_impl(asyncio_state *state, TaskObj *task, PyObject *exc)
         if (PyErr_GivenExceptionMatches(exc, PyExc_KeyboardInterrupt) ||
             PyErr_GivenExceptionMatches(exc, PyExc_SystemExit))
         {
-            /* We've got a KeyboardInterrupt or a SystemError; re-raise it */
+            /* The exception is re-raised to the event loop, so it cannot be
+               lost even if loop shutdown prevents this task from being
+               awaited. */
+            task->task_log_tb = 0;
             PyErr_SetRaisedException(exc);
             goto fail;
         }