rtc.EventEmitter contravariance (#304)

livekit-api/livekit/api/access_token.py

@@ -154,9 +154,13 @@ def to_jwt(self) -> str:
             {
                 "sub": self.identity,
                 "iss": self.api_key,
-                "nbf": calendar.timegm(datetime.datetime.now(datetime.timezone.utc).utctimetuple()),
+                "nbf": calendar.timegm(
+                    datetime.datetime.now(datetime.timezone.utc).utctimetuple()
+                ),
                 "exp": calendar.timegm(
-                    (datetime.datetime.now(datetime.timezone.utc) + self.ttl).utctimetuple()
+                    (
+                        datetime.datetime.now(datetime.timezone.utc) + self.ttl
+                    ).utctimetuple()
                 ),
             }
         )

livekit-rtc/livekit/rtc/event_emitter.py

@@ -3,17 +3,17 @@
 
 from .log import logger
 
-T = TypeVar("T")
+T_contra = TypeVar("T_contra", contravariant=True)
 
 
-class EventEmitter(Generic[T]):
+class EventEmitter(Generic[T_contra]):
     def __init__(self) -> None:
         """
         Initialize a new instance of EventEmitter.
         """
-        self._events: Dict[T, Set[Callable]] = dict()
+        self._events: Dict[T_contra, Set[Callable]] = dict()
 
-    def emit(self, event: T, *args) -> None:
+    def emit(self, event: T_contra, *args) -> None:
         """
         Trigger all callbacks associated with the given event.
 
@@ -60,7 +60,7 @@ def greet(name):
                 except Exception:
                     logger.exception(f"failed to emit event {event}")
 
-    def once(self, event: T, callback: Optional[Callable] = None) -> Callable:
+    def once(self, event: T_contra, callback: Optional[Callable] = None) -> Callable:
         """
         Register a callback to be called only once when the event is emitted.
 
@@ -116,7 +116,7 @@ def decorator(callback: Callable) -> Callable:
 
             return decorator
 
-    def on(self, event: T, callback: Optional[Callable] = None) -> Callable:
+    def on(self, event: T_contra, callback: Optional[Callable] = None) -> Callable:
         """
         Register a callback to be called whenever the event is emitted.
 
@@ -168,7 +168,7 @@ def decorator(callback: Callable) -> Callable:
 
             return decorator
 
-    def off(self, event: T, callback: Callable) -> None:
+    def off(self, event: T_contra, callback: Callable) -> None:
         """
         Unregister a callback from an event.