Hotfix to load policies saved with SB3 <= v1.6 (#1234)

* Hotfix to load policies saved with SB3 <= v1.6

* Add warning and test

* Update doc

docs/misc/changelog.rst

@@ -4,9 +4,17 @@ Changelog
 ==========
 
 
-Release 1.7.0a9 (WIP)
+Release 1.7.0a10 (WIP)
 --------------------------
 
+.. note::
+
+  A2C and PPO saved with SB3 < 1.7.0 will show a warning about
+  missing keys in the state dict when loaded with SB3 >= 1.7.0.
+  To suppress the warning, simply save the model again.
+  You can find more info in `issue #1233 <https://github.com/DLR-RM/stable-baselines3/issues/1233>`_
+
+
 Breaking Changes:
 ^^^^^^^^^^^^^^^^^
 - Removed deprecated ``create_eval_env``, ``eval_env``, ``eval_log_path``, ``n_eval_episodes`` and ``eval_freq`` parameters,

stable_baselines3/common/base_class.py

@@ -3,6 +3,7 @@
 import io
 import pathlib
 import time
+import warnings
 from abc import ABC, abstractmethod
 from collections import deque
 from typing import Any, Dict, Iterable, List, Optional, Tuple, Type, TypeVar, Union
@@ -705,8 +706,25 @@ class BaseAlgorithm(ABC):
         model.__dict__.update(kwargs)
         model._setup_model()
 
-        # put state_dicts back in place
-        model.set_parameters(params, exact_match=True, device=device)
+        try:
+            # put state_dicts back in place
+            model.set_parameters(params, exact_match=True, device=device)
+        except RuntimeError as e:
+            # Patch to load Policy saved using SB3 < 1.7.0
+            # the error is probably due to old policy being loaded
+            # See https://github.com/DLR-RM/stable-baselines3/issues/1233
+            if "pi_features_extractor" in str(e) and "Missing key(s) in state_dict" in str(e):
+                model.set_parameters(params, exact_match=False, device=device)
+                warnings.warn(
+                    "You are probably loading a model saved with SB3 < 1.7.0, "
+                    "we deactivated exact_match so you can save the model "
+                    "again to avoid issues in the future "
+                    "(see https://github.com/DLR-RM/stable-baselines3/issues/1233 for more info). "
+                    f"Original error: {e} \n"
+                    "Note: the model should still work fine, this only a warning."
+                )
+            else:
+                raise e
 
         # put other pytorch variables back in place
         if pytorch_variables is not None:

stable_baselines3/version.txt

@@ -1 +1 @@
-1.7.0a9
+1.7.0a10

tests/test_save_load.py

@@ -338,6 +338,14 @@ def test_save_load_env_cnn(tmp_path, model_class):
     # clear file from os
     os.remove(tmp_path / "test_save.zip")
 
+    # Check we can load models saved with SB3 < 1.7.0
+    if model_class == A2C:
+        del model.policy.pi_features_extractor
+        model.save(tmp_path / "test_save")
+        with pytest.warns(UserWarning):
+            model_class.load(str(tmp_path / "test_save.zip"), env=env, **kwargs).learn(100)
+        os.remove(tmp_path / "test_save.zip")
+
 
 @pytest.mark.parametrize("model_class", [SAC, TD3, DQN])
 def test_save_load_replay_buffer(tmp_path, model_class):