[RLlib] Make envs specifiable in configs by their class path. (#8750)

rllib/BUILD

@@ -1120,7 +1120,7 @@ py_test(
 py_test(
     name = "tests/test_avail_actions_qmix",
     tags = ["tests_dir", "tests_dir_A"],
-    size = "small",
+    size = "medium",
     srcs = ["tests/test_avail_actions_qmix.py"]
 )
 

rllib/agents/trainer.py

@@ -20,6 +20,7 @@ from ray.rllib.utils import FilterManager, deep_update, merge_dicts
 from ray.rllib.utils.framework import check_framework, try_import_tf
 from ray.rllib.utils.annotations import override, PublicAPI, DeveloperAPI
 from ray.rllib.utils.deprecation import DEPRECATED_VALUE, deprecation_warning
+from ray.rllib.utils.from_config import from_config
 from ray.tune.registry import ENV_CREATOR, register_env, _global_registry
 from ray.tune.trainable import Trainable
 from ray.tune.trial import ExportFormat
@@ -535,8 +536,14 @@ class Trainer(Trainable):
         env = self._env_id
         if env:
             config["env"] = env
+            # An already registered env.
             if _global_registry.contains(ENV_CREATOR, env):
                 self.env_creator = _global_registry.get(ENV_CREATOR, env)
+            # A class specifier.
+            elif "." in env:
+                self.env_creator = \
+                    lambda env_config: from_config(env, env_config)
+            # Try gym.
             else:
                 import gym  # soft dependency
                 self.env_creator = lambda env_config: gym.make(env)

rllib/utils/from_config.py

@@ -73,6 +73,8 @@ def from_config(cls, config=None, **kwargs):
         pass
     if isinstance(config, dict):
         type_ = config.pop("type", None)
+        if type_ is None and isinstance(cls, str):
+            type_ = cls
         ctor_kwargs = config
         # Give kwargs priority over things defined in config dict.
         # This way, one can pass a generic `spec` and then override single

rllib/utils/tests/test_framework_agnostic_components.py

@@ -165,6 +165,14 @@ class TestFrameWorkAgnosticComponents(unittest.TestCase):
                 value = sess.run(value)
             check(value, np.array([-6.6]))  # prop_b == -1.5
 
+    def test_unregistered_envs(self):
+        """Tests, whether an Env can be specified simply by its absolute class.
+        """
+        env_cls = "ray.rllib.examples.env.stateless_cartpole.StatelessCartPole"
+        env = from_config(env_cls, {"config": 42.0})
+        state = env.reset()
+        self.assertTrue(state.shape == (2, ))
+
 
 if __name__ == "__main__":
     import pytest