Fix resource warning (#1742)

* Fix resource warning

* Add test and update changelog

* Fix for new mypy version

docs/misc/changelog.rst

@@ -3,7 +3,7 @@
 Changelog
 ==========
 
-Release 2.2.0a11 (WIP)
+Release 2.2.0a12 (WIP)
 --------------------------
 **Support for options at reset, bug fixes and better error messages**
 
@@ -32,6 +32,7 @@ Bug Fixes:
 - Fixed success reward dtype in ``SimpleMultiObsEnv`` (@NixGD)
 - Fixed check_env for Sequence observation space (@corentinlger)
 - Prevents instantiating BitFlippingEnv with conflicting observation spaces (@kylesayrs)
+- Fixed ResourceWarning when loading and saving models (files were not closed)
 
 `SB3-Contrib`_
 ^^^^^^^^^^^^^^

stable_baselines3/common/save_util.py

@@ -308,28 +308,28 @@ def save_to_zip_file(
     :param pytorch_variables: Other PyTorch variables expected to contain name and value of the variable.
     :param verbose: Verbosity level: 0 for no output, 1 for info messages, 2 for debug messages
     """
-    save_path = open_path(save_path, "w", verbose=0, suffix="zip")
-    # data/params can be None, so do not
-    # try to serialize them blindly
-    if data is not None:
-        serialized_data = data_to_json(data)
-
-    # Create a zip-archive and write our objects there.
-    with zipfile.ZipFile(save_path, mode="w") as archive:
-        # Do not try to save "None" elements
+    with open_path(save_path, "w", verbose=0, suffix="zip") as save_path:
+        # data/params can be None, so do not
+        # try to serialize them blindly
         if data is not None:
-            archive.writestr("data", serialized_data)
-        if pytorch_variables is not None:
-            with archive.open("pytorch_variables.pth", mode="w", force_zip64=True) as pytorch_variables_file:
-                th.save(pytorch_variables, pytorch_variables_file)
-        if params is not None:
-            for file_name, dict_ in params.items():
-                with archive.open(file_name + ".pth", mode="w", force_zip64=True) as param_file:
-                    th.save(dict_, param_file)
-        # Save metadata: library version when file was saved
-        archive.writestr("_stable_baselines3_version", sb3.__version__)
-        # Save system info about the current python env
-        archive.writestr("system_info.txt", get_system_info(print_info=False)[1])
+            serialized_data = data_to_json(data)
+
+        # Create a zip-archive and write our objects there.
+        with zipfile.ZipFile(save_path, mode="w") as archive:
+            # Do not try to save "None" elements
+            if data is not None:
+                archive.writestr("data", serialized_data)
+            if pytorch_variables is not None:
+                with archive.open("pytorch_variables.pth", mode="w", force_zip64=True) as pytorch_variables_file:
+                    th.save(pytorch_variables, pytorch_variables_file)
+            if params is not None:
+                for file_name, dict_ in params.items():
+                    with archive.open(file_name + ".pth", mode="w", force_zip64=True) as param_file:
+                        th.save(dict_, param_file)
+            # Save metadata: library version when file was saved
+            archive.writestr("_stable_baselines3_version", sb3.__version__)
+            # Save system info about the current python env
+            archive.writestr("system_info.txt", get_system_info(print_info=False)[1])
 
 
 def save_to_pkl(path: Union[str, pathlib.Path, io.BufferedIOBase], obj: Any, verbose: int = 0) -> None:
@@ -450,4 +450,6 @@ def load_from_zip_file(
     except zipfile.BadZipFile as e:
         # load_path wasn't a zip file
         raise ValueError(f"Error: the file {load_path} wasn't a zip-file") from e
+    finally:
+        load_path.close()
     return data, params, pytorch_variables

stable_baselines3/common/vec_env/subproc_vec_env.py

@@ -128,14 +128,14 @@ class SubprocVecEnv(VecEnv):
     def step_wait(self) -> VecEnvStepReturn:
         results = [remote.recv() for remote in self.remotes]
         self.waiting = False
-        obs, rews, dones, infos, self.reset_infos = zip(*results)
-        return _flatten_obs(obs, self.observation_space), np.stack(rews), np.stack(dones), infos
+        obs, rews, dones, infos, self.reset_infos = zip(*results)  # type: ignore[assignment]
+        return _flatten_obs(obs, self.observation_space), np.stack(rews), np.stack(dones), infos  # type: ignore[return-value]
 
     def reset(self) -> VecEnvObs:
         for env_idx, remote in enumerate(self.remotes):
             remote.send(("reset", (self._seeds[env_idx], self._options[env_idx])))
         results = [remote.recv() for remote in self.remotes]
-        obs, self.reset_infos = zip(*results)
+        obs, self.reset_infos = zip(*results)  # type: ignore[assignment]
         # Seeds and options are only used once
         self._reset_seeds()
         self._reset_options()

stable_baselines3/version.txt

@@ -1 +1 @@
-2.2.0a11
+2.2.0a12

tests/test_save_load.py

@@ -747,3 +747,12 @@ def test_dqn_target_update_interval(tmp_path):
     model = DQN.load(tmp_path / "dqn_cartpole")
     os.remove(tmp_path / "dqn_cartpole.zip")
     assert model.target_update_interval == 100
+
+
+# Turn warnings into errors
+@pytest.mark.filterwarnings("error")
+def test_no_resource_warning(tmp_path):
+    # check that files are properly closed
+    # Create a PPO agent and save it
+    PPO("MlpPolicy", "CartPole-v1").save(tmp_path / "dqn_cartpole")
+    PPO.load(tmp_path / "dqn_cartpole")