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bpo-39529: Deprecate creating new event loop in asyncio.get_event_loop() (GH-23554)
asyncio.get_event_loop() emits now a deprecation warning when it creates a new event loop. In future releases it will became an alias of asyncio.get_running_loop().
1 parent face87c commit 172c0f2

16 files changed

+568
-183
lines changed

‎Doc/library/asyncio-eventloop.rst

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Original file line numberDiff line numberDiff line change
@@ -53,6 +53,11 @@ an event loop:
5353
Consider also using the :func:`asyncio.run` function instead of using
5454
lower level functions to manually create and close an event loop.
5555

56+
.. deprecated:: 3.10
57+
Deprecation warning is emitted if there is no running event loop.
58+
If future Python releases this function will be an alias of
59+
:func:`get_running_loop`.
60+
5661
.. function:: set_event_loop(loop)
5762

5863
Set *loop* as a current event loop for the current OS thread.

‎Doc/library/asyncio-future.rst

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Original file line numberDiff line numberDiff line change
@@ -57,12 +57,20 @@ Future Functions
5757
.. versionchanged:: 3.5.1
5858
The function accepts any :term:`awaitable` object.
5959

60+
.. deprecated:: 3.10
61+
Deprecation warning is emitted if *obj* is not a Future-like object
62+
and *loop* is not specified and there is no running event loop.
63+
6064

6165
.. function:: wrap_future(future, *, loop=None)
6266

6367
Wrap a :class:`concurrent.futures.Future` object in a
6468
:class:`asyncio.Future` object.
6569

70+
.. deprecated:: 3.10
71+
Deprecation warning is emitted if *future* is not a Future-like object
72+
and *loop* is not specified and there is no running event loop.
73+
6674

6775
Future Object
6876
=============
@@ -90,6 +98,10 @@ Future Object
9098
.. versionchanged:: 3.7
9199
Added support for the :mod:`contextvars` module.
92100

101+
.. deprecated:: 3.10
102+
Deprecation warning is emitted if *loop* is not specified
103+
and there is no running event loop.
104+
93105
.. method:: result()
94106

95107
Return the result of the Future.

‎Doc/library/asyncio-task.rst

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Original file line numberDiff line numberDiff line change
@@ -397,6 +397,11 @@ Running Tasks Concurrently
397397
If the *gather* itself is cancelled, the cancellation is
398398
propagated regardless of *return_exceptions*.
399399

400+
.. deprecated:: 3.10
401+
Deprecation warning is emitted if no positional arguments are provided
402+
or not all positional arguments are Future-like objects
403+
and there is no running event loop.
404+
400405

401406
Shielding From Cancellation
402407
===========================
@@ -434,6 +439,10 @@ Shielding From Cancellation
434439
except CancelledError:
435440
res = None
436441

442+
.. deprecated:: 3.10
443+
Deprecation warning is emitted if *aw* is not Future-like object
444+
and there is no running event loop.
445+
437446

438447
Timeouts
439448
========
@@ -593,6 +602,10 @@ Waiting Primitives
593602
earliest_result = await coro
594603
# ...
595604

605+
.. deprecated:: 3.10
606+
Deprecation warning is emitted if not all awaitable objects in the *aws*
607+
iterable are Future-like objects and there is no running event loop.
608+
596609

597610
Running in Threads
598611
==================
@@ -775,6 +788,10 @@ Task Object
775788
.. deprecated-removed:: 3.8 3.10
776789
The *loop* parameter.
777790

791+
.. deprecated:: 3.10
792+
Deprecation warning is emitted if *loop* is not specified
793+
and there is no running event loop.
794+
778795
.. method:: cancel(msg=None)
779796

780797
Request the Task to be cancelled.

‎Doc/whatsnew/3.10.rst

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@@ -1349,6 +1349,19 @@ Deprecated
13491349
scheduled for removal in Python 3.12.
13501350
(Contributed by Erlend E. Aasland in :issue:`42264`.)
13511351
1352+
* :func:`asyncio.get_event_loop` emits now a deprecation warning if there is
1353+
no running event loop. In future it will be an alias of
1354+
:func:`~asyncio.get_running_loop`.
1355+
:mod:`asyncio` functions which implicitly create a :class:`~asyncio.Future`
1356+
or :class:`~asyncio.Task` objects emit now
1357+
a deprecation warning if there is no running event loop and no explicit
1358+
*loop* argument is passed: :func:`~asyncio.ensure_future`,
1359+
:func:`~asyncio.wrap_future`, :func:`~asyncio.gather`,
1360+
:func:`~asyncio.shield`, :func:`~asyncio.as_completed` and constructors of
1361+
:class:`~asyncio.Future`, :class:`~asyncio.Task`,
1362+
:class:`~asyncio.StreamReader`, :class:`~asyncio.StreamReaderProtocol`.
1363+
(Contributed by Serhiy Storchaka in :issue:`39529`.)
1364+
13521365
* The undocumented built-in function ``sqlite3.enable_shared_cache`` is now
13531366
deprecated, scheduled for removal in Python 3.12. Its use is strongly
13541367
discouraged by the SQLite3 documentation. See `the SQLite3 docs

‎Lib/asyncio/events.py

Lines changed: 10 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -759,9 +759,16 @@ def get_event_loop():
759759
the result of `get_event_loop_policy().get_event_loop()` call.
760760
"""
761761
# NOTE: this function is implemented in C (see _asynciomodule.c)
762+
return _py__get_event_loop()
763+
764+
765+
def _get_event_loop(stacklevel=3):
762766
current_loop = _get_running_loop()
763767
if current_loop is not None:
764768
return current_loop
769+
import warnings
770+
warnings.warn('There is no current event loop',
771+
DeprecationWarning, stacklevel=stacklevel)
765772
return get_event_loop_policy().get_event_loop()
766773

767774

@@ -791,14 +798,15 @@ def set_child_watcher(watcher):
791798
_py__set_running_loop = _set_running_loop
792799
_py_get_running_loop = get_running_loop
793800
_py_get_event_loop = get_event_loop
801+
_py__get_event_loop = _get_event_loop
794802

795803

796804
try:
797805
# get_event_loop() is one of the most frequently called
798806
# functions in asyncio. Pure Python implementation is
799807
# about 4 times slower than C-accelerated.
800808
from _asyncio import (_get_running_loop, _set_running_loop,
801-
get_running_loop, get_event_loop)
809+
get_running_loop, get_event_loop, _get_event_loop)
802810
except ImportError:
803811
pass
804812
else:
@@ -807,3 +815,4 @@ def set_child_watcher(watcher):
807815
_c__set_running_loop = _set_running_loop
808816
_c_get_running_loop = get_running_loop
809817
_c_get_event_loop = get_event_loop
818+
_c__get_event_loop = _get_event_loop

‎Lib/asyncio/futures.py

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -76,7 +76,7 @@ def __init__(self, *, loop=None):
7676
the default event loop.
7777
"""
7878
if loop is None:
79-
self._loop = events.get_event_loop()
79+
self._loop = events._get_event_loop()
8080
else:
8181
self._loop = loop
8282
self._callbacks = []
@@ -408,7 +408,7 @@ def wrap_future(future, *, loop=None):
408408
assert isinstance(future, concurrent.futures.Future), \
409409
f'concurrent.futures.Future is expected, got {future!r}'
410410
if loop is None:
411-
loop = events.get_event_loop()
411+
loop = events._get_event_loop()
412412
new_future = loop.create_future()
413413
_chain_future(future, new_future)
414414
return new_future

‎Lib/asyncio/streams.py

Lines changed: 9 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -125,7 +125,7 @@ class FlowControlMixin(protocols.Protocol):
125125

126126
def __init__(self, loop=None):
127127
if loop is None:
128-
self._loop = events.get_event_loop()
128+
self._loop = events._get_event_loop(stacklevel=4)
129129
else:
130130
self._loop = loop
131131
self._paused = False
@@ -283,9 +283,13 @@ def _get_close_waiter(self, stream):
283283
def __del__(self):
284284
# Prevent reports about unhandled exceptions.
285285
# Better than self._closed._log_traceback = False hack
286-
closed = self._closed
287-
if closed.done() and not closed.cancelled():
288-
closed.exception()
286+
try:
287+
closed = self._closed
288+
except AttributeError:
289+
pass # failed constructor
290+
else:
291+
if closed.done() and not closed.cancelled():
292+
closed.exception()
289293

290294

291295
class StreamWriter:
@@ -381,7 +385,7 @@ def __init__(self, limit=_DEFAULT_LIMIT, loop=None):
381385

382386
self._limit = limit
383387
if loop is None:
384-
self._loop = events.get_event_loop()
388+
self._loop = events._get_event_loop()
385389
else:
386390
self._loop = loop
387391
self._buffer = bytearray()

‎Lib/asyncio/tasks.py

Lines changed: 23 additions & 19 deletions
Original file line numberDiff line numberDiff line change
@@ -549,7 +549,7 @@ def as_completed(fs, *, timeout=None):
549549
from .queues import Queue # Import here to avoid circular import problem.
550550
done = Queue()
551551

552-
loop = events.get_event_loop()
552+
loop = events._get_event_loop()
553553
todo = {ensure_future(f, loop=loop) for f in set(fs)}
554554
timeout_handle = None
555555

@@ -616,23 +616,26 @@ def ensure_future(coro_or_future, *, loop=None):
616616
617617
If the argument is a Future, it is returned directly.
618618
"""
619-
if coroutines.iscoroutine(coro_or_future):
620-
if loop is None:
621-
loop = events.get_event_loop()
622-
task = loop.create_task(coro_or_future)
623-
if task._source_traceback:
624-
del task._source_traceback[-1]
625-
return task
626-
elif futures.isfuture(coro_or_future):
619+
return _ensure_future(coro_or_future, loop=loop)
620+
621+
622+
def _ensure_future(coro_or_future, *, loop=None):
623+
if futures.isfuture(coro_or_future):
627624
if loop is not None and loop is not futures._get_loop(coro_or_future):
628625
raise ValueError('The future belongs to a different loop than '
629-
'the one specified as the loop argument')
626+
'the one specified as the loop argument')
630627
return coro_or_future
631-
elif inspect.isawaitable(coro_or_future):
632-
return ensure_future(_wrap_awaitable(coro_or_future), loop=loop)
633-
else:
634-
raise TypeError('An asyncio.Future, a coroutine or an awaitable is '
635-
'required')
628+
629+
if not coroutines.iscoroutine(coro_or_future):
630+
if inspect.isawaitable(coro_or_future):
631+
coro_or_future = _wrap_awaitable(coro_or_future)
632+
else:
633+
raise TypeError('An asyncio.Future, a coroutine or an awaitable '
634+
'is required')
635+
636+
if loop is None:
637+
loop = events._get_event_loop(stacklevel=4)
638+
return loop.create_task(coro_or_future)
636639

637640

638641
@types.coroutine
@@ -655,7 +658,8 @@ class _GatheringFuture(futures.Future):
655658
cancelled.
656659
"""
657660

658-
def __init__(self, children, *, loop=None):
661+
def __init__(self, children, *, loop):
662+
assert loop is not None
659663
super().__init__(loop=loop)
660664
self._children = children
661665
self._cancel_requested = False
@@ -706,7 +710,7 @@ def gather(*coros_or_futures, return_exceptions=False):
706710
gather won't cancel any other awaitables.
707711
"""
708712
if not coros_or_futures:
709-
loop = events.get_event_loop()
713+
loop = events._get_event_loop()
710714
outer = loop.create_future()
711715
outer.set_result([])
712716
return outer
@@ -773,7 +777,7 @@ def _done_callback(fut):
773777
loop = None
774778
for arg in coros_or_futures:
775779
if arg not in arg_to_fut:
776-
fut = ensure_future(arg, loop=loop)
780+
fut = _ensure_future(arg, loop=loop)
777781
if loop is None:
778782
loop = futures._get_loop(fut)
779783
if fut is not arg:
@@ -823,7 +827,7 @@ def shield(arg):
823827
except CancelledError:
824828
res = None
825829
"""
826-
inner = ensure_future(arg)
830+
inner = _ensure_future(arg)
827831
if inner.done():
828832
# Shortcut.
829833
return inner

‎Lib/test/test_asyncio/test_events.py

Lines changed: 67 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -2702,14 +2702,18 @@ def get_event_loop(self):
27022702
asyncio.set_event_loop_policy(Policy())
27032703
loop = asyncio.new_event_loop()
27042704

2705-
with self.assertRaises(TestError):
2706-
asyncio.get_event_loop()
2705+
with self.assertWarns(DeprecationWarning) as cm:
2706+
with self.assertRaises(TestError):
2707+
asyncio.get_event_loop()
2708+
self.assertEqual(cm.warnings[0].filename, __file__)
27072709
asyncio.set_event_loop(None)
2708-
with self.assertRaises(TestError):
2709-
asyncio.get_event_loop()
2710+
with self.assertWarns(DeprecationWarning) as cm:
2711+
with self.assertRaises(TestError):
2712+
asyncio.get_event_loop()
2713+
self.assertEqual(cm.warnings[0].filename, __file__)
27102714

27112715
with self.assertRaisesRegex(RuntimeError, 'no running'):
2712-
self.assertIs(asyncio.get_running_loop(), None)
2716+
asyncio.get_running_loop()
27132717
self.assertIs(asyncio._get_running_loop(), None)
27142718

27152719
async def func():
@@ -2720,20 +2724,73 @@ async def func():
27202724
loop.run_until_complete(func())
27212725

27222726
asyncio.set_event_loop(loop)
2723-
with self.assertRaises(TestError):
2724-
asyncio.get_event_loop()
2727+
with self.assertWarns(DeprecationWarning) as cm:
2728+
with self.assertRaises(TestError):
2729+
asyncio.get_event_loop()
2730+
self.assertEqual(cm.warnings[0].filename, __file__)
27252731

27262732
asyncio.set_event_loop(None)
2727-
with self.assertRaises(TestError):
2728-
asyncio.get_event_loop()
2733+
with self.assertWarns(DeprecationWarning) as cm:
2734+
with self.assertRaises(TestError):
2735+
asyncio.get_event_loop()
2736+
self.assertEqual(cm.warnings[0].filename, __file__)
27292737

27302738
finally:
27312739
asyncio.set_event_loop_policy(old_policy)
27322740
if loop is not None:
27332741
loop.close()
27342742

27352743
with self.assertRaisesRegex(RuntimeError, 'no running'):
2736-
self.assertIs(asyncio.get_running_loop(), None)
2744+
asyncio.get_running_loop()
2745+
2746+
self.assertIs(asyncio._get_running_loop(), None)
2747+
2748+
def test_get_event_loop_returns_running_loop2(self):
2749+
old_policy = asyncio.get_event_loop_policy()
2750+
try:
2751+
asyncio.set_event_loop_policy(asyncio.DefaultEventLoopPolicy())
2752+
loop = asyncio.new_event_loop()
2753+
self.addCleanup(loop.close)
2754+
2755+
with self.assertWarns(DeprecationWarning) as cm:
2756+
loop2 = asyncio.get_event_loop()
2757+
self.addCleanup(loop2.close)
2758+
self.assertEqual(cm.warnings[0].filename, __file__)
2759+
asyncio.set_event_loop(None)
2760+
with self.assertWarns(DeprecationWarning) as cm:
2761+
with self.assertRaisesRegex(RuntimeError, 'no current'):
2762+
asyncio.get_event_loop()
2763+
self.assertEqual(cm.warnings[0].filename, __file__)
2764+
2765+
with self.assertRaisesRegex(RuntimeError, 'no running'):
2766+
asyncio.get_running_loop()
2767+
self.assertIs(asyncio._get_running_loop(), None)
2768+
2769+
async def func():
2770+
self.assertIs(asyncio.get_event_loop(), loop)
2771+
self.assertIs(asyncio.get_running_loop(), loop)
2772+
self.assertIs(asyncio._get_running_loop(), loop)
2773+
2774+
loop.run_until_complete(func())
2775+
2776+
asyncio.set_event_loop(loop)
2777+
with self.assertWarns(DeprecationWarning) as cm:
2778+
self.assertIs(asyncio.get_event_loop(), loop)
2779+
self.assertEqual(cm.warnings[0].filename, __file__)
2780+
2781+
asyncio.set_event_loop(None)
2782+
with self.assertWarns(DeprecationWarning) as cm:
2783+
with self.assertRaisesRegex(RuntimeError, 'no current'):
2784+
asyncio.get_event_loop()
2785+
self.assertEqual(cm.warnings[0].filename, __file__)
2786+
2787+
finally:
2788+
asyncio.set_event_loop_policy(old_policy)
2789+
if loop is not None:
2790+
loop.close()
2791+
2792+
with self.assertRaisesRegex(RuntimeError, 'no running'):
2793+
asyncio.get_running_loop()
27372794

27382795
self.assertIs(asyncio._get_running_loop(), None)
27392796

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