Use _typeshed.Self with __enter__ (#5719)

stdlib/asyncio/unix_events.pyi

@@ -1,22 +1,19 @@
 import sys
 import types
+from _typeshed import Self
 from socket import socket
-from typing import Any, Callable, Optional, Type, TypeVar
+from typing import Any, Callable, Optional, Type
 
 from .base_events import Server
 from .events import AbstractEventLoop, BaseDefaultEventLoopPolicy, _ProtocolFactory, _SSLContext
 from .selector_events import BaseSelectorEventLoop
 
-_T1 = TypeVar("_T1", bound=AbstractChildWatcher)
-_T2 = TypeVar("_T2", bound=SafeChildWatcher)
-_T3 = TypeVar("_T3", bound=FastChildWatcher)
-
 class AbstractChildWatcher:
     def add_child_handler(self, pid: int, callback: Callable[..., Any], *args: Any) -> None: ...
     def remove_child_handler(self, pid: int) -> bool: ...
     def attach_loop(self, loop: Optional[AbstractEventLoop]) -> None: ...
     def close(self) -> None: ...
-    def __enter__(self: _T1) -> _T1: ...
+    def __enter__(self: Self) -> Self: ...
     def __exit__(
         self, typ: Optional[Type[BaseException]], exc: Optional[BaseException], tb: Optional[types.TracebackType]
     ) -> None: ...
@@ -27,10 +24,10 @@ class BaseChildWatcher(AbstractChildWatcher):
     def __init__(self) -> None: ...
 
 class SafeChildWatcher(BaseChildWatcher):
-    def __enter__(self: _T2) -> _T2: ...
+    def __enter__(self: Self) -> Self: ...
 
 class FastChildWatcher(BaseChildWatcher):
-    def __enter__(self: _T3) -> _T3: ...
+    def __enter__(self: Self) -> Self: ...
 
 class _UnixSelectorEventLoop(BaseSelectorEventLoop):
     if sys.version_info < (3, 7):
@@ -55,15 +52,12 @@ DefaultEventLoopPolicy = _UnixDefaultEventLoopPolicy
 if sys.version_info >= (3, 8):
 
     from typing import Protocol
-
-    _T4 = TypeVar("_T4", bound=MultiLoopChildWatcher)
-    _T5 = TypeVar("_T5", bound=ThreadedChildWatcher)
     class _Warn(Protocol):
         def __call__(
             self, message: str, category: Optional[Type[Warning]] = ..., stacklevel: int = ..., source: Optional[Any] = ...
         ) -> None: ...
     class MultiLoopChildWatcher(AbstractChildWatcher):
-        def __enter__(self: _T4) -> _T4: ...
+        def __enter__(self: Self) -> Self: ...
     class ThreadedChildWatcher(AbstractChildWatcher):
-        def __enter__(self: _T5) -> _T5: ...
+        def __enter__(self: Self) -> Self: ...
         def __del__(self, _warn: _Warn = ...) -> None: ...