Literal: always import from typing_extensions for simplicity (#4219)

stdlib/3/asyncio/base_events.pyi

@@ -2,6 +2,7 @@ from socket import socket, _Address, _RetAddress
 import ssl
 import sys
 from typing import Any, Awaitable, Callable, Dict, Generator, IO, List, Optional, Sequence, Tuple, TypeVar, Union, overload
+from typing_extensions import Literal
 from abc import ABCMeta
 from asyncio.futures import Future
 from asyncio.events import AbstractEventLoop, AbstractServer, Handle, TimerHandle
@@ -10,11 +11,6 @@ from asyncio.tasks import Task
 from asyncio.transports import BaseTransport
 from _types import FileDescriptorLike
 
-if sys.version_info >= (3, 8):
-    from typing import Literal
-else:
-    from typing_extensions import Literal
-
 if sys.version_info >= (3, 7):
     from contextvars import Context
 

stdlib/3/asyncio/base_futures.pyi

@@ -1,13 +1,8 @@
-
-import sys
 import contextvars
 from typing import List, Tuple, Callable, Sequence
-from . import futures
+from typing_extensions import Literal
 
-if sys.version_info >= (3, 8):
-    from typing import Literal
-else:
-    from typing_extensions import Literal
+from . import futures
 
 _PENDING: Literal["PENDING"]  # undocumented
 _CANCELLED: Literal["CANCELLED"]  # undocumented

stdlib/3/asyncio/sslproto.pyi

@@ -3,6 +3,7 @@ import sys
 import ssl
 
 from typing import ClassVar, Optional, List, Tuple, Callable, Dict, Any, Deque
+from typing_extensions import Literal
 
 from . import transports
 from . import constants
@@ -10,11 +11,6 @@ from . import events
 from . import protocols
 from . import futures
 
-if sys.version_info >= (3, 8):
-    from typing import Literal
-else:
-    from typing_extensions import Literal
-
 def _create_transport_context(server_side: bool, server_hostname: Optional[str]) -> ssl.SSLContext: ...
 
 _UNWRAPPED: Literal["UNWRAPPED"]

stdlib/3/asyncio/tasks.pyi

@@ -3,15 +3,11 @@ import sys
 from typing import (
     Any, TypeVar, Set, List, TextIO, Union, Tuple, Generic, Generator, Iterable, Awaitable, overload, Iterator, Optional,
 )
+from typing_extensions import Literal
 from types import FrameType
 from .events import AbstractEventLoop
 from .futures import Future
 
-if sys.version_info >= (3, 8):
-    from typing import Literal
-else:
-    from typing_extensions import Literal
-
 _T = TypeVar('_T')
 _T1 = TypeVar('_T1')
 _T2 = TypeVar('_T2')