GH-93896: AAlways set event loop in asyncio.run and IsolatedAsyncioTestCase (GH-94593)

(cherry picked from commit 14fea6b4)

Co-authored-by: Kumar Aditya <59607654+kumaraditya303@users.noreply.github.com>

Lib/asyncio/runners.py

@@ -53,6 +53,7 @@ def __init__(self, *, debug=None, loop_factory=None):
         self._loop = None
         self._context = None
         self._interrupt_count = 0
+        self._set_event_loop = False
 
     def __enter__(self):
         self._lazy_init()
@@ -71,6 +72,8 @@ def close(self):
             loop.run_until_complete(loop.shutdown_asyncgens())
             loop.run_until_complete(loop.shutdown_default_executor())
         finally:
+            if self._set_event_loop:
+                events.set_event_loop(None)
             loop.close()
             self._loop = None
             self._state = _State.CLOSED
@@ -112,6 +115,8 @@ def run(self, coro, *, context=None):
 
         self._interrupt_count = 0
         try:
+            if self._set_event_loop:
+                events.set_event_loop(self._loop)
             return self._loop.run_until_complete(task)
         except exceptions.CancelledError:
             if self._interrupt_count > 0 and task.uncancel() == 0:
@@ -131,6 +136,7 @@ def _lazy_init(self):
             return
         if self._loop_factory is None:
             self._loop = events.new_event_loop()
+            self._set_event_loop = True
         else:
             self._loop = self._loop_factory()
         if self._debug is not None:

Lib/test/test_asyncio/test_runners.py

@@ -199,6 +199,18 @@ async def main():
         self.assertIsNone(spinner.ag_frame)
         self.assertFalse(spinner.ag_running)
 
+    def test_asyncio_run_set_event_loop(self):
+        #See https://github.com/python/cpython/issues/93896
+
+        async def main():
+            await asyncio.sleep(0)
+            return 42
+
+        policy = asyncio.get_event_loop_policy()
+        policy.set_event_loop = mock.Mock()
+        asyncio.run(main())
+        self.assertTrue(policy.set_event_loop.called)
+
 
 class RunnerTests(BaseTest):
 

Misc/NEWS.d/next/Library/2022-07-06-06-02-02.gh-issue-93896.vIgWGr.rst

+Fix :func:`asyncio.run` and :class:`unittest.IsolatedAsyncioTestCase` to always the set event loop as it was done in Python 3.10 and earlier. Patch by Kumar Aditya.