Use forward type annotations

Besides improving code legibility, they are necessary for the rendered
documentation to be properly cross-referenced (otherwise the types
appear just as a string, without links).

Signed-off-by: Leandro Lucarella <[email protected]>

Author: llucax

src/frequenz/channels/anycast.py

@@ -3,6 +3,8 @@
 
 """A channel for sending data across async tasks."""
 
+from __future__ import annotations
+
 from asyncio import Condition
 from collections import deque
 from typing import Deque, Generic, Optional
@@ -88,15 +90,15 @@ async def close(self) -> None:
         async with self.recv_cv:
             self.recv_cv.notify_all()
 
-    def get_sender(self) -> "Sender[T]":
+    def get_sender(self) -> Sender[T]:
         """Create a new sender.
 
         Returns:
             A Sender instance attached to the Anycast channel.
         """
         return Sender(self)
 
-    def get_receiver(self) -> "Receiver[T]":
+    def get_receiver(self) -> Receiver[T]:
         """Create a new receiver.
 
         Returns:

src/frequenz/channels/base_classes.py

@@ -3,6 +3,8 @@
 
 """Baseclasses for Channel Sender and Receiver."""
 
+from __future__ import annotations
+
 from abc import ABC, abstractmethod
 from typing import Callable, Generic, Optional, TypeVar
 
@@ -37,7 +39,7 @@ async def receive(self) -> Optional[T]:
             None, if the channel is closed, a message otherwise.
         """
 
-    def __aiter__(self) -> "Receiver[T]":
+    def __aiter__(self) -> Receiver[T]:
         """Initialize the async iterator over received values.
 
         Returns:
@@ -60,7 +62,7 @@ async def __anext__(self) -> T:
             raise StopAsyncIteration
         return received
 
-    def map(self, call: Callable[[T], U]) -> "Receiver[U]":
+    def map(self, call: Callable[[T], U]) -> Receiver[U]:
         """Return a receiver with `call` applied on incoming messages.
 
         Args:
@@ -71,7 +73,7 @@ def map(self, call: Callable[[T], U]) -> "Receiver[U]":
         """
         return _Map(self, call)
 
-    def into_peekable(self) -> "Peekable[T]":
+    def into_peekable(self) -> Peekable[T]:
         """Convert the `Receiver` implementation into a `Peekable`.
 
         Once this function has been called, the receiver will no longer be

src/frequenz/channels/bidirectional.py

@@ -3,6 +3,8 @@
 
 """An abstraction to provide bi-directional communication between actors."""
 
+from __future__ import annotations
+
 from typing import Generic, Optional
 
 from frequenz.channels.base_classes import Receiver, Sender, T, U
@@ -35,7 +37,7 @@ def __init__(self, client_id: str, service_id: str) -> None:
         )
 
     @property
-    def client_handle(self) -> "BidirectionalHandle[T, U]":
+    def client_handle(self) -> BidirectionalHandle[T, U]:
         """Get a BidirectionalHandle for the client to use.
 
         Returns:
@@ -44,7 +46,7 @@ def client_handle(self) -> "BidirectionalHandle[T, U]":
         return self._client_handle
 
     @property
-    def service_handle(self) -> "BidirectionalHandle[U, T]":
+    def service_handle(self) -> BidirectionalHandle[U, T]:
         """Get a BidirectionalHandle for the service to use.
 
         Returns:

src/frequenz/channels/broadcast.py

@@ -3,6 +3,8 @@
 
 """A channel to broadcast messages to all receivers."""
 
+from __future__ import annotations
+
 import logging
 from asyncio import Condition
 from collections import deque
@@ -110,7 +112,7 @@ def _drop_receiver(self, uuid: UUID) -> None:
         if uuid in self.receivers:
             del self.receivers[uuid]
 
-    def get_sender(self) -> "Sender[T]":
+    def get_sender(self) -> Sender[T]:
         """Create a new broadcast sender.
 
         Returns:
@@ -120,7 +122,7 @@ def get_sender(self) -> "Sender[T]":
 
     def get_receiver(
         self, name: Optional[str] = None, maxsize: int = 50
-    ) -> "Receiver[T]":
+    ) -> Receiver[T]:
         """Create a new broadcast receiver.
 
         Broadcast receivers have their own buffer, and when messages are not
@@ -137,13 +139,13 @@ def get_receiver(
         uuid = uuid4()
         if name is None:
             name = str(uuid)
-        recv: "Receiver[T]" = Receiver(uuid, name, maxsize, self)
+        recv: Receiver[T] = Receiver(uuid, name, maxsize, self)
         self.receivers[uuid] = recv
         if self._resend_latest and self._latest is not None:
             recv.enqueue(self._latest)
         return recv
 
-    def get_peekable(self) -> "Peekable[T]":
+    def get_peekable(self) -> Peekable[T]:
         """Create a new Peekable for the broadcast channel.
 
         A Peekable provides a [peek()][frequenz.channels.Peekable.peek] method
@@ -283,7 +285,7 @@ async def receive(self) -> Optional[T]:
         ret = self._q.popleft()
         return ret
 
-    def into_peekable(self) -> "Peekable[T]":
+    def into_peekable(self) -> Peekable[T]:
         """Convert the `Receiver` implementation into a `Peekable`.
 
         Once this function has been called, the receiver will no longer be