refactor(rl): update type hints for learner and actor functions

src/lerobot/rl/actor.py

@@ -46,11 +46,10 @@ For more details on the complete HILSerl training workflow, see:
 https://github.com/michel-aractingi/lerobot-hilserl-guide
 """
 
-from __future__ import annotations
-
 import logging
 import os
 import time
+from collections.abc import Generator
 from functools import lru_cache
 from queue import Empty
 from typing import TYPE_CHECKING, Any
@@ -433,10 +432,10 @@ def act_with_policy(
 
 
 def establish_learner_connection(
-    stub: services_pb2_grpc.LearnerServiceStub,
+    stub: "services_pb2_grpc.LearnerServiceStub",
     shutdown_event: Any,  # Event
     attempts: int = 30,
-):
+) -> bool:
     """Establish a connection with the learner.
 
     Args:
@@ -466,12 +465,14 @@ def establish_learner_connection(
 def learner_service_client(
     host: str = "127.0.0.1",
     port: int = 50051,
-) -> tuple[services_pb2_grpc.LearnerServiceStub, grpc.Channel]:
-    """
-    Returns a client for the learner service.
+) -> "tuple[services_pb2_grpc.LearnerServiceStub, grpc.Channel]":
+    """Return a client for the learner service.
 
     GRPC uses HTTP/2, which is a binary protocol and multiplexes requests over a single connection.
     So we need to create only one client and reuse it.
+
+    Returns:
+        tuple[services_pb2_grpc.LearnerServiceStub, grpc.Channel]: The stub and the channel.
     """
 
     channel = grpc.insecure_channel(
@@ -487,15 +488,17 @@ def receive_policy(
     cfg: TrainRLServerPipelineConfig,
     parameters_queue: Queue,
     shutdown_event: Any,  # Event
-    learner_client: services_pb2_grpc.LearnerServiceStub | None = None,
-    grpc_channel: grpc.Channel | None = None,
-):
+    learner_client: "services_pb2_grpc.LearnerServiceStub | None" = None,
+    grpc_channel: "grpc.Channel | None" = None,
+) -> None:
     """Receive parameters from the learner.
 
     Args:
         cfg (TrainRLServerPipelineConfig): The configuration for the actor.
         parameters_queue (Queue): The queue to receive the parameters.
         shutdown_event (Event): The event to check if the process should shutdown.
+        learner_client (services_pb2_grpc.LearnerServiceStub | None): Optional pre-created stub.
+        grpc_channel (grpc.Channel | None): Optional pre-created channel.
     """
     logging.info("[ACTOR] Start receiving parameters from the Learner")
     if not use_threads(cfg):
@@ -539,11 +542,10 @@ def send_transitions(
     cfg: TrainRLServerPipelineConfig,
     transitions_queue: Queue,
     shutdown_event: Any,  # Event
-    learner_client: services_pb2_grpc.LearnerServiceStub | None = None,
-    grpc_channel: grpc.Channel | None = None,
-) -> services_pb2.Empty:
-    """
-    Sends transitions to the learner.
+    learner_client: "services_pb2_grpc.LearnerServiceStub | None" = None,
+    grpc_channel: "grpc.Channel | None" = None,
+) -> None:
+    """Send transitions to the learner.
 
     This function continuously retrieves messages from the queue and processes:
 
@@ -551,6 +553,13 @@ def send_transitions(
         - A batch of transitions (observation, action, reward, next observation) is collected.
         - Transitions are moved to the CPU and serialized using PyTorch.
         - The serialized data is wrapped in a `services_pb2.Transition` message and sent to the learner.
+
+    Args:
+        cfg (TrainRLServerPipelineConfig): The configuration for the actor.
+        transitions_queue (Queue): The queue to receive the transitions.
+        shutdown_event (Event): The event to check if the process should shutdown.
+        learner_client (services_pb2_grpc.LearnerServiceStub | None): Optional pre-created stub.
+        grpc_channel (grpc.Channel | None): Optional pre-created channel.
     """
 
     if not use_threads(cfg):
@@ -589,17 +598,23 @@ def send_interactions(
     cfg: TrainRLServerPipelineConfig,
     interactions_queue: Queue,
     shutdown_event: Any,  # Event
-    learner_client: services_pb2_grpc.LearnerServiceStub | None = None,
-    grpc_channel: grpc.Channel | None = None,
-) -> services_pb2.Empty:
-    """
-    Sends interactions to the learner.
+    learner_client: "services_pb2_grpc.LearnerServiceStub | None" = None,
+    grpc_channel: "grpc.Channel | None" = None,
+) -> None:
+    """Send interactions to the learner.
 
     This function continuously retrieves messages from the queue and processes:
 
     - Interaction Messages:
         - Contains useful statistics about episodic rewards and policy timings.
         - The message is serialized using `pickle` and sent to the learner.
+
+    Args:
+        cfg (TrainRLServerPipelineConfig): The configuration for the actor.
+        interactions_queue (Queue): The queue to receive the interactions.
+        shutdown_event (Event): The event to check if the process should shutdown.
+        learner_client (services_pb2_grpc.LearnerServiceStub | None): Optional pre-created stub.
+        grpc_channel (grpc.Channel | None): Optional pre-created channel.
     """
 
     if not use_threads(cfg):
@@ -642,7 +657,7 @@ def transitions_stream(
     shutdown_event: Any,  # Event
     transitions_queue: Queue,
     timeout: float,
-) -> services_pb2.Empty:
+) -> "Generator[Any, None, services_pb2.Empty]":
     while not shutdown_event.is_set():
         try:
             message = transitions_queue.get(block=True, timeout=timeout)
@@ -661,7 +676,7 @@ def interactions_stream(
     shutdown_event: Any,  # Event
     interactions_queue: Queue,
     timeout: float,
-) -> services_pb2.Empty:
+) -> "Generator[Any, None, services_pb2.Empty]":
     while not shutdown_event.is_set():
         try:
             message = interactions_queue.get(block=True, timeout=timeout)

src/lerobot/rl/learner.py

@@ -44,8 +44,6 @@ For more details on the complete HILSerl training workflow, see:
 https://github.com/michel-aractingi/lerobot-hilserl-guide
 """
 
-from __future__ import annotations
-
 import logging
 import os
 import shutil