gh-93453: No longer create an event loop in get_event_loop() (#98440)

asyncio.get_event_loop() now always return either running event loop or
the result of get_event_loop_policy().get_event_loop() call. The latter
should now raise an RuntimeError if no current event loop was set
instead of creating and setting a new event loop.

It affects also a number of asyncio functions and constructors which
call get_event_loop() implicitly: ensure_future(), shield(), gather(),
etc.

DeprecationWarning is no longer emitted if there is no running event loop but
the current event loop was set.

Co-authored-by: Łukasz Langa <lukasz@langa.pl>

1 files changed, 19 insertions, 37 deletions

diff --git a/Lib/test/test_asyncio/test_tasks.py b/Lib/test/test_asyncio/test_tasks.py
index d8ba2f4..bb1ffdf 100644
--- a/Lib/test/test_asyncio/test_tasks.py
+++ b/Lib/test/test_asyncio/test_tasks.py
@@ -196,10 +196,8 @@ class BaseTaskTests:
 
         a = notmuch()
         self.addCleanup(a.close)
-        with self.assertWarns(DeprecationWarning) as cm:
-            with self.assertRaisesRegex(RuntimeError, 'There is no current event loop'):
-                asyncio.ensure_future(a)
-        self.assertEqual(cm.filename, __file__)
+        with self.assertRaisesRegex(RuntimeError, 'no current event loop'):
+            asyncio.ensure_future(a)
 
         async def test():
             return asyncio.ensure_future(notmuch())
@@ -209,12 +207,10 @@ class BaseTaskTests:
         self.assertTrue(t.done())
         self.assertEqual(t.result(), 'ok')
 
-        # Deprecated in 3.10
+        # Deprecated in 3.10, undeprecated in 3.12
         asyncio.set_event_loop(self.loop)
         self.addCleanup(asyncio.set_event_loop, None)
-        with self.assertWarns(DeprecationWarning) as cm:
-            t = asyncio.ensure_future(notmuch())
-        self.assertEqual(cm.filename, __file__)
+        t = asyncio.ensure_future(notmuch())
         self.assertIs(t._loop, self.loop)
         self.loop.run_until_complete(t)
         self.assertTrue(t.done())
@@ -1532,10 +1528,8 @@ class BaseTaskTests:
         self.addCleanup(a.close)
 
         futs = asyncio.as_completed([a])
-        with self.assertWarns(DeprecationWarning) as cm:
-            with self.assertRaisesRegex(RuntimeError, 'There is no current event loop'):
-                list(futs)
-        self.assertEqual(cm.filename, __file__)
+        with self.assertRaisesRegex(RuntimeError, 'no current event loop'):
+            list(futs)
 
     def test_as_completed_coroutine_use_running_loop(self):
         loop = self.new_test_loop()
@@ -1965,10 +1959,8 @@ class BaseTaskTests:
 
         inner = coro()
         self.addCleanup(inner.close)
-        with self.assertWarns(DeprecationWarning) as cm:
-            with self.assertRaisesRegex(RuntimeError, 'There is no current event loop'):
-                asyncio.shield(inner)
-        self.assertEqual(cm.filename, __file__)
+        with self.assertRaisesRegex(RuntimeError, 'no current event loop'):
+            asyncio.shield(inner)
 
     def test_shield_coroutine_use_running_loop(self):
         async def coro():
@@ -1982,15 +1974,13 @@ class BaseTaskTests:
         self.assertEqual(res, 42)
 
     def test_shield_coroutine_use_global_loop(self):
-        # Deprecated in 3.10
+        # Deprecated in 3.10, undeprecated in 3.12
         async def coro():
             return 42
 
         asyncio.set_event_loop(self.loop)
         self.addCleanup(asyncio.set_event_loop, None)
-        with self.assertWarns(DeprecationWarning) as cm:
-            outer = asyncio.shield(coro())
-        self.assertEqual(cm.filename, __file__)
+        outer = asyncio.shield(coro())
         self.assertEqual(outer._loop, self.loop)
         res = self.loop.run_until_complete(outer)
         self.assertEqual(res, 42)
@@ -2827,7 +2817,7 @@ class BaseCurrentLoopTests:
         self.assertIsNone(asyncio.current_task(loop=self.loop))
 
     def test_current_task_no_running_loop_implicit(self):
-        with self.assertRaises(RuntimeError):
+        with self.assertRaisesRegex(RuntimeError, 'no running event loop'):
             asyncio.current_task()
 
     def test_current_task_with_implicit_loop(self):
@@ -2991,10 +2981,8 @@ class FutureGatherTests(GatherTestsBase, test_utils.TestCase):
         return asyncio.gather(*args, **kwargs)
 
     def test_constructor_empty_sequence_without_loop(self):
-        with self.assertWarns(DeprecationWarning) as cm:
-            with self.assertRaises(RuntimeError):
-                asyncio.gather()
-        self.assertEqual(cm.filename, __file__)
+        with self.assertRaisesRegex(RuntimeError, 'no current event loop'):
+            asyncio.gather()
 
     def test_constructor_empty_sequence_use_running_loop(self):
         async def gather():
@@ -3007,12 +2995,10 @@ class FutureGatherTests(GatherTestsBase, test_utils.TestCase):
         self.assertEqual(fut.result(), [])
 
     def test_constructor_empty_sequence_use_global_loop(self):
-        # Deprecated in 3.10
+        # Deprecated in 3.10, undeprecated in 3.12
         asyncio.set_event_loop(self.one_loop)
         self.addCleanup(asyncio.set_event_loop, None)
-        with self.assertWarns(DeprecationWarning) as cm:
-            fut = asyncio.gather()
-        self.assertEqual(cm.filename, __file__)
+        fut = asyncio.gather()
         self.assertIsInstance(fut, asyncio.Future)
         self.assertIs(fut._loop, self.one_loop)
         self._run_loop(self.one_loop)
@@ -3100,10 +3086,8 @@ class CoroutineGatherTests(GatherTestsBase, test_utils.TestCase):
         self.addCleanup(gen1.close)
         gen2 = coro()
         self.addCleanup(gen2.close)
-        with self.assertWarns(DeprecationWarning) as cm:
-            with self.assertRaises(RuntimeError):
-                asyncio.gather(gen1, gen2)
-        self.assertEqual(cm.filename, __file__)
+        with self.assertRaisesRegex(RuntimeError, 'no current event loop'):
+            asyncio.gather(gen1, gen2)
 
     def test_constructor_use_running_loop(self):
         async def coro():
@@ -3117,16 +3101,14 @@ class CoroutineGatherTests(GatherTestsBase, test_utils.TestCase):
         self.one_loop.run_until_complete(fut)
 
     def test_constructor_use_global_loop(self):
-        # Deprecated in 3.10
+        # Deprecated in 3.10, undeprecated in 3.12
         async def coro():
             return 'abc'
         asyncio.set_event_loop(self.other_loop)
         self.addCleanup(asyncio.set_event_loop, None)
         gen1 = coro()
         gen2 = coro()
-        with self.assertWarns(DeprecationWarning) as cm:
-            fut = asyncio.gather(gen1, gen2)
-        self.assertEqual(cm.filename, __file__)
+        fut = asyncio.gather(gen1, gen2)
         self.assertIs(fut._loop, self.other_loop)
         self.other_loop.run_until_complete(fut)