gh-127949: deprecate asyncio policy classes (#128216)

4 files changed, 31 insertions, 15 deletions

diff --git a/Lib/asyncio/__init__.py b/Lib/asyncio/__init__.py
index 03165a4..edb615b 100644
--- a/Lib/asyncio/__init__.py
+++ b/Lib/asyncio/__init__.py
@@ -45,3 +45,19 @@ if sys.platform == 'win32':  # pragma: no cover
 else:
     from .unix_events import *  # pragma: no cover
     __all__ += unix_events.__all__
+
+def __getattr__(name: str):
+    import warnings
+
+    deprecated = {
+        "AbstractEventLoopPolicy",
+        "DefaultEventLoopPolicy",
+        "WindowsSelectorEventLoopPolicy",
+        "WindowsProactorEventLoopPolicy",
+    }
+    if name in deprecated:
+        warnings._deprecated(f"asyncio.{name}", remove=(3, 16))
+        # deprecated things have underscores in front of them
+        return globals()["_" + name]
+
+    raise AttributeError(f"module {__name__!r} has no attribute {name!r}")
diff --git a/Lib/asyncio/events.py b/Lib/asyncio/events.py
index 1449245..3ade774 100644
--- a/Lib/asyncio/events.py
+++ b/Lib/asyncio/events.py
@@ -5,7 +5,7 @@
 # SPDX-FileCopyrightText: Copyright (c) 2015-2021 MagicStack Inc.  http://magic.io
 
 __all__ = (
-    'AbstractEventLoopPolicy',
+    '_AbstractEventLoopPolicy',
     'AbstractEventLoop', 'AbstractServer',
     'Handle', 'TimerHandle',
     '_get_event_loop_policy',
@@ -632,7 +632,7 @@ class AbstractEventLoop:
         raise NotImplementedError
 
 
-class AbstractEventLoopPolicy:
+class _AbstractEventLoopPolicy:
     """Abstract policy for accessing the event loop."""
 
     def get_event_loop(self):
@@ -655,7 +655,7 @@ class AbstractEventLoopPolicy:
         the current context, set_event_loop must be called explicitly."""
         raise NotImplementedError
 
-class BaseDefaultEventLoopPolicy(AbstractEventLoopPolicy):
+class _BaseDefaultEventLoopPolicy(_AbstractEventLoopPolicy):
     """Default policy implementation for accessing the event loop.
 
     In this policy, each thread has its own event loop.  However, we
@@ -758,8 +758,8 @@ def _init_event_loop_policy():
     global _event_loop_policy
     with _lock:
         if _event_loop_policy is None:  # pragma: no branch
-            from . import DefaultEventLoopPolicy
-            _event_loop_policy = DefaultEventLoopPolicy()
+            from . import _DefaultEventLoopPolicy
+            _event_loop_policy = _DefaultEventLoopPolicy()
 
 
 def _get_event_loop_policy():
@@ -777,7 +777,7 @@ def _set_event_loop_policy(policy):
 
     If policy is None, the default policy is restored."""
     global _event_loop_policy
-    if policy is not None and not isinstance(policy, AbstractEventLoopPolicy):
+    if policy is not None and not isinstance(policy, _AbstractEventLoopPolicy):
         raise TypeError(f"policy must be an instance of AbstractEventLoopPolicy or None, not '{type(policy).__name__}'")
     _event_loop_policy = policy
 
@@ -838,7 +838,7 @@ if hasattr(os, 'fork'):
     def on_fork():
         # Reset the loop and wakeupfd in the forked child process.
         if _event_loop_policy is not None:
-            _event_loop_policy._local = BaseDefaultEventLoopPolicy._Local()
+            _event_loop_policy._local = _BaseDefaultEventLoopPolicy._Local()
         _set_running_loop(None)
         signal.set_wakeup_fd(-1)
 
diff --git a/Lib/asyncio/unix_events.py b/Lib/asyncio/unix_events.py
index 0227eb5..f69c6a6 100644
--- a/Lib/asyncio/unix_events.py
+++ b/Lib/asyncio/unix_events.py
@@ -28,7 +28,7 @@ from .log import logger
 
 __all__ = (
     'SelectorEventLoop',
-    'DefaultEventLoopPolicy',
+    '_DefaultEventLoopPolicy',
     'EventLoop',
 )
 
@@ -963,11 +963,11 @@ def can_use_pidfd():
     return True
 
 
-class _UnixDefaultEventLoopPolicy(events.BaseDefaultEventLoopPolicy):
+class _UnixDefaultEventLoopPolicy(events._BaseDefaultEventLoopPolicy):
     """UNIX event loop policy"""
     _loop_factory = _UnixSelectorEventLoop
 
 
 SelectorEventLoop = _UnixSelectorEventLoop
-DefaultEventLoopPolicy = _UnixDefaultEventLoopPolicy
+_DefaultEventLoopPolicy = _UnixDefaultEventLoopPolicy
 EventLoop = SelectorEventLoop
diff --git a/Lib/asyncio/windows_events.py b/Lib/asyncio/windows_events.py
index bf99bc2..5f75b17 100644
--- a/Lib/asyncio/windows_events.py
+++ b/Lib/asyncio/windows_events.py
@@ -29,8 +29,8 @@ from .log import logger
 
 __all__ = (
     'SelectorEventLoop', 'ProactorEventLoop', 'IocpProactor',
-    'DefaultEventLoopPolicy', 'WindowsSelectorEventLoopPolicy',
-    'WindowsProactorEventLoopPolicy', 'EventLoop',
+    '_DefaultEventLoopPolicy', '_WindowsSelectorEventLoopPolicy',
+    '_WindowsProactorEventLoopPolicy', 'EventLoop',
 )
 
 
@@ -891,13 +891,13 @@ class _WindowsSubprocessTransport(base_subprocess.BaseSubprocessTransport):
 SelectorEventLoop = _WindowsSelectorEventLoop
 
 
-class WindowsSelectorEventLoopPolicy(events.BaseDefaultEventLoopPolicy):
+class _WindowsSelectorEventLoopPolicy(events._BaseDefaultEventLoopPolicy):
     _loop_factory = SelectorEventLoop
 
 
-class WindowsProactorEventLoopPolicy(events.BaseDefaultEventLoopPolicy):
+class _WindowsProactorEventLoopPolicy(events._BaseDefaultEventLoopPolicy):
     _loop_factory = ProactorEventLoop
 
 
-DefaultEventLoopPolicy = WindowsProactorEventLoopPolicy
+_DefaultEventLoopPolicy = _WindowsProactorEventLoopPolicy
 EventLoop = ProactorEventLoop