Fix return type of evaluate_actions (#1118)

* Fix return type of ActorCriticPolicy.evaluate_actions to optional entropy tensor

* Update changelog.rst

docs/misc/changelog.rst

@@ -22,6 +22,7 @@ SB3-Contrib
 
 Bug Fixes:
 ^^^^^^^^^^
+- Fix return type of ``evaluate_actions`` in ``ActorCritcPolicy`` to reflect that entropy is an optional tensor (@Rocamonde)
 
 Deprecations:
 ^^^^^^^^^^^^^

stable_baselines3/common/policies.py

@@ -613,7 +613,7 @@ class ActorCriticPolicy(BasePolicy):
         """
         return self.get_distribution(observation).get_actions(deterministic=deterministic)
 
-    def evaluate_actions(self, obs: th.Tensor, actions: th.Tensor) -> Tuple[th.Tensor, th.Tensor, th.Tensor]:
+    def evaluate_actions(self, obs: th.Tensor, actions: th.Tensor) -> Tuple[th.Tensor, th.Tensor, Optional[th.Tensor]]:
         """
         Evaluate actions according to the current policy,
         given the observations.
@@ -629,7 +629,8 @@ class ActorCriticPolicy(BasePolicy):
         distribution = self._get_action_dist_from_latent(latent_pi)
         log_prob = distribution.log_prob(actions)
         values = self.value_net(latent_vf)
-        return values, log_prob, distribution.entropy()
+        entropy = distribution.entropy()
+        return values, log_prob, entropy
 
     def get_distribution(self, obs: th.Tensor) -> Distribution:
         """

tests/test_distributions.py

@@ -77,6 +77,8 @@ def test_get_distribution(dummy_model_distribution_obs_and_actions):
         distribution = model.policy.get_distribution(observations)
         log_prob_2 = distribution.log_prob(actions)
         entropy_2 = distribution.entropy()
+        assert entropy_1 is not None
+        assert entropy_2 is not None
         assert th.allclose(log_prob_1, log_prob_2)
         assert th.allclose(entropy_1, entropy_2)