Fix: Make actor ID optional for single-network torch policies

maze/core/agent/torch_policy.py

@@ -134,13 +134,17 @@ def compute_logits_dict(self, observation: Any, actor_id: ActorIDType = None) ->
         obs_t = convert_to_torch(observation, device=self._device, cast=None, in_place=True)
         return self.network_for(actor_id)(obs_t)
 
-    def network_for(self, actor_id: ActorIDType) -> nn.Module:
+    def network_for(self, actor_id: Optional[ActorIDType]) -> nn.Module:
         """Helper function for returning a network for the given policy ID (using either just the sub-step ID
         or the full Actor ID as key, depending on the separated agent networks mode.
 
         :param actor_id: Actor ID to get a network for
         :return: Network corresponding to the given policy ID.
         """
+        if actor_id is None:
+            assert len(self.networks) == 1, "multiple networks are available, please specify the actor ID explicitly"
+            return list(self.networks.values())[0]
+
         network_key = actor_id if actor_id[0] in self.substeps_with_separate_agent_nets else actor_id[0]
         return self.networks[network_key]
 

maze/test/core/agent/test_torch_policy.py

@@ -0,0 +1,13 @@
+"""Torch policy mechanics tests."""
+
+from maze.test.shared_test_utils.helper_functions import build_dummy_maze_env, \
+    flatten_concat_probabilistic_policy_for_env
+
+
+def test_actor_id_is_optional_for_single_network_policies():
+    env = build_dummy_maze_env()
+    policy = flatten_concat_probabilistic_policy_for_env(env)
+
+    obs = env.reset()
+    action = policy.compute_action(obs)  # No actor ID provided
+    assert action in env.action_space