gh-127949: deprecate `asyncio.set_event_loop` (#128218)

Deprecate `asyncio.set_event_loop` to be removed in Python 3.16. 

3 files changed, 24 insertions, 14 deletions

diff --git a/Lib/asyncio/__main__.py b/Lib/asyncio/__main__.py
index 95c636f..662ba64 100644
--- a/Lib/asyncio/__main__.py
+++ b/Lib/asyncio/__main__.py
@@ -149,7 +149,7 @@ if __name__ == '__main__':
 
     return_code = 0
     loop = asyncio.new_event_loop()
-    asyncio.set_event_loop(loop)
+    asyncio._set_event_loop(loop)
 
     repl_locals = {'asyncio': asyncio}
     for key in {'__name__', '__package__',
diff --git a/Lib/asyncio/events.py b/Lib/asyncio/events.py
index 3ade774..6e291d2 100644
--- a/Lib/asyncio/events.py
+++ b/Lib/asyncio/events.py
@@ -5,16 +5,22 @@
 # SPDX-FileCopyrightText: Copyright (c) 2015-2021 MagicStack Inc.  http://magic.io
 
 __all__ = (
-    '_AbstractEventLoopPolicy',
-    'AbstractEventLoop', 'AbstractServer',
-    'Handle', 'TimerHandle',
-    '_get_event_loop_policy',
-    'get_event_loop_policy',
-    '_set_event_loop_policy',
-    'set_event_loop_policy',
-    'get_event_loop', 'set_event_loop', 'new_event_loop',
-    '_set_running_loop', 'get_running_loop',
-    '_get_running_loop',
+    "_AbstractEventLoopPolicy",
+    "AbstractEventLoop",
+    "AbstractServer",
+    "Handle",
+    "TimerHandle",
+    "_get_event_loop_policy",
+    "get_event_loop_policy",
+    "_set_event_loop_policy",
+    "set_event_loop_policy",
+    "get_event_loop",
+    "_set_event_loop",
+    "set_event_loop",
+    "new_event_loop",
+    "_set_running_loop",
+    "get_running_loop",
+    "_get_running_loop",
 )
 
 import contextvars
@@ -801,9 +807,13 @@ def get_event_loop():
     return _get_event_loop_policy().get_event_loop()
 
 
+def _set_event_loop(loop):
+    _get_event_loop_policy().set_event_loop(loop)
+
 def set_event_loop(loop):
     """Equivalent to calling get_event_loop_policy().set_event_loop(loop)."""
-    _get_event_loop_policy().set_event_loop(loop)
+    warnings._deprecated('asyncio.set_event_loop', remove=(3,16))
+    _set_event_loop(loop)
 
 
 def new_event_loop():
diff --git a/Lib/asyncio/runners.py b/Lib/asyncio/runners.py
index 0e63c34..b9adf29 100644
--- a/Lib/asyncio/runners.py
+++ b/Lib/asyncio/runners.py
@@ -74,7 +74,7 @@ class Runner:
                 loop.shutdown_default_executor(constants.THREAD_JOIN_TIMEOUT))
         finally:
             if self._set_event_loop:
-                events.set_event_loop(None)
+                events._set_event_loop(None)
             loop.close()
             self._loop = None
             self._state = _State.CLOSED
@@ -147,7 +147,7 @@ class Runner:
             if not self._set_event_loop:
                 # Call set_event_loop only once to avoid calling
                 # attach_loop multiple times on child watchers
-                events.set_event_loop(self._loop)
+                events._set_event_loop(self._loop)
                 self._set_event_loop = True
         else:
             self._loop = self._loop_factory()