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>

Doc/library/asyncio-eventloop.rst

@@ -43,10 +43,12 @@ an event loop:
 
    Get the current event loop.
 
-   If there is no current event loop set in the current OS thread,
-   the OS thread is main, and :func:`set_event_loop` has not yet
-   been called, asyncio will create a new event loop and set it as the
-   current one.
+   When called from a coroutine or a callback (e.g. scheduled with
+   call_soon or similar API), this function will always return the
+   running event loop.
+
+   If there is no running event loop set, the function will return
+   the result of calling ``get_event_loop_policy().get_event_loop()``.
 
    Because this function has rather complex behavior (especially
    when custom event loop policies are in use), using the
@@ -57,11 +59,11 @@ an event loop:
    instead of using these lower level functions to manually create and close an
    event loop.
 
-   .. deprecated:: 3.10
-      Emits a deprecation warning if there is no running event loop.
-      In future Python releases, this function may become an alias of
-      :func:`get_running_loop` and will accordingly raise a
-      :exc:`RuntimeError` if there is no running event loop.
+   .. note::
+      In Python versions 3.10.0--3.10.8 and 3.11.0 this function
+      (and other functions which used it implicitly) emitted a
+      :exc:`DeprecationWarning` if there was no running event loop, even if
+      the current loop was set.
 
 .. function:: set_event_loop(loop)
 

Doc/library/asyncio-llapi-index.rst

@@ -19,7 +19,7 @@ Obtaining the Event Loop
       - The **preferred** function to get the running event loop.
 
     * - :func:`asyncio.get_event_loop`
-      - Get an event loop instance (current or via the policy).
+      - Get an event loop instance (running or current via the current policy).
 
     * - :func:`asyncio.set_event_loop`
       - Set the event loop as current via the current policy.

Doc/library/asyncio-policy.rst

@@ -116,6 +116,10 @@ asyncio ships with the following built-in policies:
 
       On Windows, :class:`ProactorEventLoop` is now used by default.
 
+   .. versionchanged:: 3.12
+      :meth:`get_event_loop` now raises a :exc:`RuntimeError` if there is no
+      current event loop set.
+
 
 .. class:: WindowsSelectorEventLoopPolicy
 

Doc/whatsnew/3.12.rst

@@ -686,6 +686,18 @@ Changes in the Python API
   around process-global resources, which are best managed from the main interpreter.
   (Contributed by Dong-hee Na in :gh:`99127`.)
 
+* :func:`asyncio.get_event_loop` and many other :mod:`asyncio` functions like
+  :func:`~asyncio.ensure_future`, :func:`~asyncio.shield` or
+  :func:`~asyncio.gather`, and also the
+  :meth:`~asyncio.BaseDefaultEventLoopPolicy.get_event_loop` method of
+  :class:`~asyncio.BaseDefaultEventLoopPolicy` now raise a :exc:`RuntimeError`
+  if called when there is no running event loop and the current event loop was
+  not set.
+  Previously they implicitly created and set a new current event loop.
+  :exc:`DeprecationWarning` is no longer emitted if there is no running
+  event loop but the current event loop is set in the policy.
+  (Contributed by Serhiy Storchaka in :gh:`93453`.)
+
 
 Build Changes
 =============

Lib/asyncio/events.py

@@ -619,7 +619,7 @@ def get_event_loop(self):
 
         Returns an event loop object implementing the BaseEventLoop interface,
         or raises an exception in case no event loop has been set for the
-        current context and the current policy does not specify to create one.
+        current context.
 
         It should never return None."""
         raise NotImplementedError
@@ -672,11 +672,6 @@ def get_event_loop(self):
 
         Returns an instance of EventLoop or raises an exception.
         """
-        if (self._local._loop is None and
-                not self._local._set_called and
-                threading.current_thread() is threading.main_thread()):
-            self.set_event_loop(self.new_event_loop())
-
         if self._local._loop is None:
             raise RuntimeError('There is no current event loop in thread %r.'
                                % threading.current_thread().name)
@@ -786,16 +781,9 @@ def get_event_loop():
     the result of `get_event_loop_policy().get_event_loop()` call.
     """
     # NOTE: this function is implemented in C (see _asynciomodule.c)
-    return _py__get_event_loop()
-
-
-def _get_event_loop(stacklevel=3):
     current_loop = _get_running_loop()
     if current_loop is not None:
         return current_loop
-    import warnings
-    warnings.warn('There is no current event loop',
-                  DeprecationWarning, stacklevel=stacklevel)
     return get_event_loop_policy().get_event_loop()
 
 
@@ -825,7 +813,6 @@ def set_child_watcher(watcher):
 _py__set_running_loop = _set_running_loop
 _py_get_running_loop = get_running_loop
 _py_get_event_loop = get_event_loop
-_py__get_event_loop = _get_event_loop
 
 
 try:
@@ -833,7 +820,7 @@ def set_child_watcher(watcher):
     # functions in asyncio.  Pure Python implementation is
     # about 4 times slower than C-accelerated.
     from _asyncio import (_get_running_loop, _set_running_loop,
-                          get_running_loop, get_event_loop, _get_event_loop)
+                          get_running_loop, get_event_loop)
 except ImportError:
     pass
 else:
@@ -842,7 +829,6 @@ def set_child_watcher(watcher):
     _c__set_running_loop = _set_running_loop
     _c_get_running_loop = get_running_loop
     _c_get_event_loop = get_event_loop
-    _c__get_event_loop = _get_event_loop
 
 
 if hasattr(os, 'fork'):

Lib/asyncio/futures.py

@@ -77,7 +77,7 @@ def __init__(self, *, loop=None):
         the default event loop.
         """
         if loop is None:
-            self._loop = events._get_event_loop()
+            self._loop = events.get_event_loop()
         else:
             self._loop = loop
         self._callbacks = []
@@ -413,7 +413,7 @@ def wrap_future(future, *, loop=None):
     assert isinstance(future, concurrent.futures.Future), \
         f'concurrent.futures.Future is expected, got {future!r}'
     if loop is None:
-        loop = events._get_event_loop()
+        loop = events.get_event_loop()
     new_future = loop.create_future()
     _chain_future(future, new_future)
     return new_future

Lib/asyncio/streams.py

@@ -125,7 +125,7 @@ class FlowControlMixin(protocols.Protocol):
 
     def __init__(self, loop=None):
         if loop is None:
-            self._loop = events._get_event_loop(stacklevel=4)
+            self._loop = events.get_event_loop()
         else:
             self._loop = loop
         self._paused = False
@@ -404,7 +404,7 @@ def __init__(self, limit=_DEFAULT_LIMIT, loop=None):
 
         self._limit = limit
         if loop is None:
-            self._loop = events._get_event_loop()
+            self._loop = events.get_event_loop()
         else:
             self._loop = loop
         self._buffer = bytearray()

Lib/asyncio/tasks.py

@@ -582,7 +582,7 @@ def as_completed(fs, *, timeout=None):
     from .queues import Queue  # Import here to avoid circular import problem.
     done = Queue()
 
-    loop = events._get_event_loop()
+    loop = events.get_event_loop()
     todo = {ensure_future(f, loop=loop) for f in set(fs)}
     timeout_handle = None
 
@@ -668,7 +668,7 @@ def _ensure_future(coro_or_future, *, loop=None):
                             'is required')
 
     if loop is None:
-        loop = events._get_event_loop(stacklevel=4)
+        loop = events.get_event_loop()
     try:
         return loop.create_task(coro_or_future)
     except RuntimeError:
@@ -749,7 +749,7 @@ def gather(*coros_or_futures, return_exceptions=False):
     gather won't cancel any other awaitables.
     """
     if not coros_or_futures:
-        loop = events._get_event_loop()
+        loop = events.get_event_loop()
         outer = loop.create_future()
         outer.set_result([])
         return outer

Lib/test/test_asyncio/test_base_events.py

@@ -746,7 +746,7 @@ async def coro():
     def test_env_var_debug(self):
         code = '\n'.join((
             'import asyncio',
-            'loop = asyncio.get_event_loop()',
+            'loop = asyncio.new_event_loop()',
             'print(loop.get_debug())'))
 
         # Test with -E to not fail if the unit test was run with

Lib/test/test_asyncio/test_events.py

@@ -2550,29 +2550,8 @@ def test_event_loop_policy(self):
     def test_get_event_loop(self):
         policy = asyncio.DefaultEventLoopPolicy()
         self.assertIsNone(policy._local._loop)
-
-        loop = policy.get_event_loop()
-        self.assertIsInstance(loop, asyncio.AbstractEventLoop)
-
-        self.assertIs(policy._local._loop, loop)
-        self.assertIs(loop, policy.get_event_loop())
-        loop.close()
-
-    def test_get_event_loop_calls_set_event_loop(self):
-        policy = asyncio.DefaultEventLoopPolicy()
-
-        with mock.patch.object(
-                policy, "set_event_loop",
-                wraps=policy.set_event_loop) as m_set_event_loop:
-
-            loop = policy.get_event_loop()
-
-            # policy._local._loop must be set through .set_event_loop()
-            # (the unix DefaultEventLoopPolicy needs this call to attach
-            # the child watcher correctly)
-            m_set_event_loop.assert_called_with(loop)
-
-        loop.close()
+        with self.assertRaisesRegex(RuntimeError, 'no current event loop'):
+            policy.get_event_loop()
 
     def test_get_event_loop_after_set_none(self):
         policy = asyncio.DefaultEventLoopPolicy()
@@ -2599,7 +2578,8 @@ def test_new_event_loop(self):
 
     def test_set_event_loop(self):
         policy = asyncio.DefaultEventLoopPolicy()
-        old_loop = policy.get_event_loop()
+        old_loop = policy.new_event_loop()
+        policy.set_event_loop(old_loop)
 
         self.assertRaises(TypeError, policy.set_event_loop, object())
 
@@ -2716,15 +2696,11 @@ def get_event_loop(self):
             asyncio.set_event_loop_policy(Policy())
             loop = asyncio.new_event_loop()
 
-            with self.assertWarns(DeprecationWarning) as cm:
-                with self.assertRaises(TestError):
-                    asyncio.get_event_loop()
-            self.assertEqual(cm.filename, __file__)
+            with self.assertRaises(TestError):
+                asyncio.get_event_loop()
             asyncio.set_event_loop(None)
-            with self.assertWarns(DeprecationWarning) as cm:
-                with self.assertRaises(TestError):
-                    asyncio.get_event_loop()
-            self.assertEqual(cm.filename, __file__)
+            with self.assertRaises(TestError):
+                asyncio.get_event_loop()
 
             with self.assertRaisesRegex(RuntimeError, 'no running'):
                 asyncio.get_running_loop()
@@ -2738,16 +2714,11 @@ async def func():
             loop.run_until_complete(func())
 
             asyncio.set_event_loop(loop)
-            with self.assertWarns(DeprecationWarning) as cm:
-                with self.assertRaises(TestError):
-                    asyncio.get_event_loop()
-            self.assertEqual(cm.filename, __file__)
-
+            with self.assertRaises(TestError):
+                asyncio.get_event_loop()
             asyncio.set_event_loop(None)
-            with self.assertWarns(DeprecationWarning) as cm:
-                with self.assertRaises(TestError):
-                    asyncio.get_event_loop()
-            self.assertEqual(cm.filename, __file__)
+            with self.assertRaises(TestError):
+                asyncio.get_event_loop()
 
         finally:
             asyncio.set_event_loop_policy(old_policy)
@@ -2766,15 +2737,11 @@ def test_get_event_loop_returns_running_loop2(self):
             loop = asyncio.new_event_loop()
             self.addCleanup(loop.close)
 
-            with self.assertWarns(DeprecationWarning) as cm:
-                loop2 = asyncio.get_event_loop()
-            self.addCleanup(loop2.close)
-            self.assertEqual(cm.filename, __file__)
+            with self.assertRaisesRegex(RuntimeError, 'no current'):
+                asyncio.get_event_loop()
             asyncio.set_event_loop(None)
-            with self.assertWarns(DeprecationWarning) as cm:
-                with self.assertRaisesRegex(RuntimeError, 'no current'):
-                    asyncio.get_event_loop()
-            self.assertEqual(cm.filename, __file__)
+            with self.assertRaisesRegex(RuntimeError, 'no current'):
+                asyncio.get_event_loop()
 
             with self.assertRaisesRegex(RuntimeError, 'no running'):
                 asyncio.get_running_loop()
@@ -2788,15 +2755,11 @@ async def func():
             loop.run_until_complete(func())
 
             asyncio.set_event_loop(loop)
-            with self.assertWarns(DeprecationWarning) as cm:
-                self.assertIs(asyncio.get_event_loop(), loop)
-            self.assertEqual(cm.filename, __file__)
+            self.assertIs(asyncio.get_event_loop(), loop)
 
             asyncio.set_event_loop(None)
-            with self.assertWarns(DeprecationWarning) as cm:
-                with self.assertRaisesRegex(RuntimeError, 'no current'):
-                    asyncio.get_event_loop()
-            self.assertEqual(cm.filename, __file__)
+            with self.assertRaisesRegex(RuntimeError, 'no current'):
+                asyncio.get_event_loop()
 
         finally:
             asyncio.set_event_loop_policy(old_policy)

Lib/test/test_asyncio/test_futures.py

@@ -146,10 +146,8 @@ def test_initial_state(self):
         self.assertTrue(f.cancelled())
 
     def test_constructor_without_loop(self):
-        with self.assertWarns(DeprecationWarning) as cm:
-            with self.assertRaisesRegex(RuntimeError, 'There is no current event loop'):
-                self._new_future()
-        self.assertEqual(cm.filename, __file__)
+        with self.assertRaisesRegex(RuntimeError, 'no current event loop'):
+            self._new_future()
 
     def test_constructor_use_running_loop(self):
         async def test():
@@ -159,12 +157,10 @@ async def test():
         self.assertIs(f.get_loop(), self.loop)
 
     def test_constructor_use_global_loop(self):
-        # 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:
-            f = self._new_future()
-        self.assertEqual(cm.filename, __file__)
+        f = self._new_future()
         self.assertIs(f._loop, self.loop)
         self.assertIs(f.get_loop(), self.loop)
 
@@ -500,10 +496,8 @@ def run(arg):
             return (arg, threading.get_ident())
         ex = concurrent.futures.ThreadPoolExecutor(1)
         f1 = ex.submit(run, 'oi')
-        with self.assertWarns(DeprecationWarning) as cm:
-            with self.assertRaises(RuntimeError):
-                asyncio.wrap_future(f1)
-        self.assertEqual(cm.filename, __file__)
+        with self.assertRaisesRegex(RuntimeError, 'no current event loop'):
+            asyncio.wrap_future(f1)
         ex.shutdown(wait=True)
 
     def test_wrap_future_use_running_loop(self):
@@ -518,16 +512,14 @@ async def test():
         ex.shutdown(wait=True)
 
     def test_wrap_future_use_global_loop(self):
-        # 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)
         def run(arg):
             return (arg, threading.get_ident())
         ex = concurrent.futures.ThreadPoolExecutor(1)
         f1 = ex.submit(run, 'oi')
-        with self.assertWarns(DeprecationWarning) as cm:
-            f2 = asyncio.wrap_future(f1)
-        self.assertEqual(cm.filename, __file__)
+        f2 = asyncio.wrap_future(f1)
         self.assertIs(self.loop, f2._loop)
         ex.shutdown(wait=True)
 

Lib/test/test_asyncio/test_streams.py

@@ -816,10 +816,8 @@ def test_read_all_from_pipe_reader(self):
         self.assertEqual(data, b'data')
 
     def test_streamreader_constructor_without_loop(self):
-        with self.assertWarns(DeprecationWarning) as cm:
-            with self.assertRaisesRegex(RuntimeError, 'There is no current event loop'):
-                asyncio.StreamReader()
-        self.assertEqual(cm.filename, __file__)
+        with self.assertRaisesRegex(RuntimeError, 'no current event loop'):
+            asyncio.StreamReader()
 
     def test_streamreader_constructor_use_running_loop(self):
         # asyncio issue #184: Ensure that StreamReaderProtocol constructor
@@ -833,21 +831,17 @@ async def test():
     def test_streamreader_constructor_use_global_loop(self):
         # asyncio issue #184: Ensure that StreamReaderProtocol constructor
         # retrieves the current loop if the loop parameter is not set
-        # Deprecated in 3.10
+        # Deprecated in 3.10, undeprecated in 3.12
         self.addCleanup(asyncio.set_event_loop, None)
         asyncio.set_event_loop(self.loop)
-        with self.assertWarns(DeprecationWarning) as cm:
-            reader = asyncio.StreamReader()
-        self.assertEqual(cm.filename, __file__)
+        reader = asyncio.StreamReader()
         self.assertIs(reader._loop, self.loop)
 
 
     def test_streamreaderprotocol_constructor_without_loop(self):
         reader = mock.Mock()
-        with self.assertWarns(DeprecationWarning) as cm:
-            with self.assertRaisesRegex(RuntimeError, 'There is no current event loop'):
-                asyncio.StreamReaderProtocol(reader)
-        self.assertEqual(cm.filename, __file__)
+        with self.assertRaisesRegex(RuntimeError, 'no current event loop'):
+            asyncio.StreamReaderProtocol(reader)
 
     def test_streamreaderprotocol_constructor_use_running_loop(self):
         # asyncio issue #184: Ensure that StreamReaderProtocol constructor
@@ -861,13 +855,11 @@ async def test():
     def test_streamreaderprotocol_constructor_use_global_loop(self):
         # asyncio issue #184: Ensure that StreamReaderProtocol constructor
         # retrieves the current loop if the loop parameter is not set
-        # Deprecated in 3.10
+        # Deprecated in 3.10, undeprecated in 3.12
         self.addCleanup(asyncio.set_event_loop, None)
         asyncio.set_event_loop(self.loop)
         reader = mock.Mock()
-        with self.assertWarns(DeprecationWarning) as cm:
-            protocol = asyncio.StreamReaderProtocol(reader)
-        self.assertEqual(cm.filename, __file__)
+        protocol = asyncio.StreamReaderProtocol(reader)
         self.assertIs(protocol._loop, self.loop)
 
     def test_multiple_drain(self):

Lib/test/test_asyncio/test_tasks.py

@@ -196,10 +196,8 @@ async def notmuch():
 
         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 @@ async def test():
         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 @@ async def coro():
         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 @@ async def coro():
 
         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 @@ async def test():
         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 @@ def test_current_task_no_running_loop(self):
         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 @@ def _gather(self, *args, **kwargs):
         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 @@ async def gather():
         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 @@ async def coro():
         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 @@ async def gather():
         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)
 

Lib/test/test_asyncio/test_unix_events.py

@@ -1775,7 +1775,8 @@ def f():
 
     def test_child_watcher_replace_mainloop_existing(self):
         policy = self.create_policy()
-        loop = policy.get_event_loop()
+        loop = policy.new_event_loop()
+        policy.set_event_loop(loop)
 
         # Explicitly setup SafeChildWatcher,
         # default ThreadedChildWatcher has no _loop property
@@ -1884,13 +1885,15 @@ async def test_fork_not_share_event_loop(self):
             # child
             try:
                 loop = asyncio.get_event_loop_policy().get_event_loop()
-                os.write(w, str(id(loop)).encode())
+            except RuntimeError:
+                os.write(w, b'NO LOOP')
+            except:
+                os.write(w, b'ERROR:' + ascii(sys.exc_info()).encode())
             finally:
                 os._exit(0)
         else:
             # parent
-            child_loop = int(os.read(r, 100).decode())
-            self.assertNotEqual(child_loop, id(loop))
+            self.assertEqual(os.read(r, 100), b'NO LOOP')
             wait_process(pid, exitcode=0)
 
     @hashlib_helper.requires_hashdigest('md5')

Lib/test/test_coroutines.py

@@ -2418,7 +2418,8 @@ class UnawaitedWarningDuringShutdownTest(unittest.TestCase):
     def test_unawaited_warning_during_shutdown(self):
         code = ("import asyncio\n"
                 "async def f(): pass\n"
-                "asyncio.gather(f())\n")
+                "async def t(): asyncio.gather(f())\n"
+                "asyncio.run(t())\n")
         assert_python_ok("-c", code)
 
         code = ("import sys\n"

Misc/NEWS.d/next/Library/2022-10-19-13-37-23.gh-issue-93453.wTB_sH.rst

@@ -0,0 +1,9 @@
+:func:`asyncio.get_event_loop` and many other :mod:`asyncio` functions like
+:func:`asyncio.ensure_future`, :func:`asyncio.shield` or
+:func:`asyncio.gather`, and also the
+:meth:`~asyncio.BaseDefaultEventLoopPolicy.get_event_loop` method of
+:class:`asyncio.BaseDefaultEventLoopPolicy` now raise a :exc:`RuntimeError`
+if called when there is no running event loop and the current event loop was
+not set. Previously they implicitly created and set a new current event
+loop. :exc:`DeprecationWarning` is no longer emitted if there is no running
+event loop but the current event loop was set.

Modules/_asynciomodule.c

@@ -357,7 +357,7 @@ set_running_loop(asyncio_state *state, PyObject *loop)
 
 
 static PyObject *
-get_event_loop(asyncio_state *state, int stacklevel)
+get_event_loop(asyncio_state *state)
 {
     PyObject *loop;
     PyObject *policy;
@@ -369,13 +369,6 @@ get_event_loop(asyncio_state *state, int stacklevel)
         return loop;
     }
 
-    if (PyErr_WarnEx(PyExc_DeprecationWarning,
-                     "There is no current event loop",
-                     stacklevel))
-    {
-        return NULL;
-    }
-
     policy = PyObject_CallNoArgs(state->asyncio_get_event_loop_policy);
     if (policy == NULL) {
         return NULL;
@@ -538,7 +531,7 @@ future_init(FutureObj *fut, PyObject *loop)
 
     if (loop == Py_None) {
         asyncio_state *state = get_asyncio_state_by_def((PyObject *)fut);
-        loop = get_event_loop(state, 1);
+        loop = get_event_loop(state);
         if (loop == NULL) {
             return -1;
         }
@@ -3229,20 +3222,7 @@ _asyncio_get_event_loop_impl(PyObject *module)
 /*[clinic end generated code: output=2a2d8b2f824c648b input=9364bf2916c8655d]*/
 {
     asyncio_state *state = get_asyncio_state(module);
-    return get_event_loop(state, 1);
-}
-
-/*[clinic input]
-_asyncio._get_event_loop
-    stacklevel: int = 3
-[clinic start generated code]*/
-
-static PyObject *
-_asyncio__get_event_loop_impl(PyObject *module, int stacklevel)
-/*[clinic end generated code: output=9c1d6d3c802e67c9 input=d17aebbd686f711d]*/
-{
-    asyncio_state *state = get_asyncio_state(module);
-    return get_event_loop(state, stacklevel-1);
+    return get_event_loop(state);
 }
 
 /*[clinic input]
@@ -3620,7 +3600,6 @@ PyDoc_STRVAR(module_doc, "Accelerator module for asyncio");
 
 static PyMethodDef asyncio_methods[] = {
     _ASYNCIO_GET_EVENT_LOOP_METHODDEF
-    _ASYNCIO__GET_EVENT_LOOP_METHODDEF
     _ASYNCIO_GET_RUNNING_LOOP_METHODDEF
     _ASYNCIO__GET_RUNNING_LOOP_METHODDEF
     _ASYNCIO__SET_RUNNING_LOOP_METHODDEF

Modules/clinic/_asynciomodule.c.h

@@ -987,68 +987,6 @@ _asyncio_get_event_loop(PyObject *module, PyObject *Py_UNUSED(ignored))
     return _asyncio_get_event_loop_impl(module);
 }
 
-PyDoc_STRVAR(_asyncio__get_event_loop__doc__,
-"_get_event_loop($module, /, stacklevel=3)\n"
-"--\n"
-"\n");
-
-#define _ASYNCIO__GET_EVENT_LOOP_METHODDEF    \
-    {"_get_event_loop", _PyCFunction_CAST(_asyncio__get_event_loop), METH_FASTCALL|METH_KEYWORDS, _asyncio__get_event_loop__doc__},
-
-static PyObject *
-_asyncio__get_event_loop_impl(PyObject *module, int stacklevel);
-
-static PyObject *
-_asyncio__get_event_loop(PyObject *module, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
-{
-    PyObject *return_value = NULL;
-    #if defined(Py_BUILD_CORE) && !defined(Py_BUILD_CORE_MODULE)
-
-    #define NUM_KEYWORDS 1
-    static struct {
-        PyGC_Head _this_is_not_used;
-        PyObject_VAR_HEAD
-        PyObject *ob_item[NUM_KEYWORDS];
-    } _kwtuple = {
-        .ob_base = PyVarObject_HEAD_INIT(&PyTuple_Type, NUM_KEYWORDS)
-        .ob_item = { &_Py_ID(stacklevel), },
-    };
-    #undef NUM_KEYWORDS
-    #define KWTUPLE (&_kwtuple.ob_base.ob_base)
-
-    #else  // !Py_BUILD_CORE
-    #  define KWTUPLE NULL
-    #endif  // !Py_BUILD_CORE
-
-    static const char * const _keywords[] = {"stacklevel", NULL};
-    static _PyArg_Parser _parser = {
-        .keywords = _keywords,
-        .fname = "_get_event_loop",
-        .kwtuple = KWTUPLE,
-    };
-    #undef KWTUPLE
-    PyObject *argsbuf[1];
-    Py_ssize_t noptargs = nargs + (kwnames ? PyTuple_GET_SIZE(kwnames) : 0) - 0;
-    int stacklevel = 3;
-
-    args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 0, 1, 0, argsbuf);
-    if (!args) {
-        goto exit;
-    }
-    if (!noptargs) {
-        goto skip_optional_pos;
-    }
-    stacklevel = _PyLong_AsInt(args[0]);
-    if (stacklevel == -1 && PyErr_Occurred()) {
-        goto exit;
-    }
-skip_optional_pos:
-    return_value = _asyncio__get_event_loop_impl(module, stacklevel);
-
-exit:
-    return return_value;
-}
-
 PyDoc_STRVAR(_asyncio_get_running_loop__doc__,
 "get_running_loop($module, /)\n"
 "--\n"
@@ -1304,4 +1242,4 @@ _asyncio__leave_task(PyObject *module, PyObject *const *args, Py_ssize_t nargs,
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=550bc6603df89ed9 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=83580c190031241c input=a9049054013a1b77]*/