fix typing in add_listener and remove_listener (#1335)

* fix typing in add_listener and remove_listener

Use the union to typecheck these functions

* add awaitable to MessageRecipient definition; remove unneeded cast

* remove unused imports

Author: tamenol

can/notifier.py

@@ -6,15 +6,15 @@
 import logging
 import threading
 import time
-from typing import Any, Callable, cast, Iterable, List, Optional, Union, Awaitable
+from typing import Callable, Iterable, List, Optional, Union, Awaitable
 
 from can.bus import BusABC
 from can.listener import Listener
 from can.message import Message
 
 logger = logging.getLogger("can.Notifier")
 
-MessageRecipient = Union[Listener, Callable[[Message], None]]
+MessageRecipient = Union[Listener, Callable[[Message], Union[Awaitable[None], None]]]
 
 
 class Notifier:
@@ -140,7 +140,7 @@ def _on_message_available(self, bus: BusABC) -> None:
 
     def _on_message_received(self, msg: Message) -> None:
         for callback in self.listeners:
-            res = cast(Union[None, Optional[Awaitable[Any]]], callback(msg))
+            res = callback(msg)
             if res is not None and self._loop is not None and asyncio.iscoroutine(res):
                 # Schedule coroutine
                 self._loop.create_task(res)
@@ -166,7 +166,7 @@ def _on_error(self, exc: Exception) -> bool:
 
         return was_handled
 
-    def add_listener(self, listener: Listener) -> None:
+    def add_listener(self, listener: MessageRecipient) -> None:
         """Add new Listener to the notification list.
         If it is already present, it will be called two times
         each time a message arrives.
@@ -175,7 +175,7 @@ def add_listener(self, listener: Listener) -> None:
         """
         self.listeners.append(listener)
 
-    def remove_listener(self, listener: Listener) -> None:
+    def remove_listener(self, listener: MessageRecipient) -> None:
         """Remove a listener from the notification list. This method
         throws an exception if the given listener is not part of the
         stored listeners.