Remove shimmy as a core dependency (#272)

Author: pseudo-rnd-thoughts

Diff for: gymnasium/envs/__init__.py

@@ -348,5 +348,17 @@
 )
 
 
+# --- For shimmy compatibility
+def _raise_shimmy_error():
+    raise ImportError(
+        "To use the gym compatibility environments, run `pip install shimmy[gym]`"
+    )
+
+
+# When installed, shimmy will re-register these environments with the correct entry_point
+register(id="GymV22Environment-v0", entry_point=_raise_shimmy_error)
+register(id="GymV26Environment-v0", entry_point=_raise_shimmy_error)
+
+
 # Hook to load plugins from entry points
 load_env_plugins()

Diff for: gymnasium/wrappers/compatibility.py

@@ -65,8 +65,8 @@ def __init__(self, old_env: LegacyEnv, render_mode: Optional[str] = None):
             render_mode (str): the render mode to use when rendering the environment, passed automatically to env.render
         """
         logger.warn(
-            "The `gymnasium.make(..., apply_api_compatibility=...)` parameter is deprecated and will be removed in v28. "
-            "Instead use `gym.make('GymV22Environment-v0', env_name=...)` or `from shimmy import GymV26CompatibilityV0`"
+            "The `gymnasium.make(..., apply_api_compatibility=...)` parameter is deprecated and will be removed in v0.28. "
+            "Instead use `gym.make('GymV22Environment-v0', env_name=...)` or `from shimmy import GymV22CompatibilityV0`"
         )
         self.metadata = getattr(old_env, "metadata", {"render_modes": []})
         self.render_mode = render_mode

Diff for: pyproject.toml

@@ -31,7 +31,6 @@ dependencies = [
     "importlib-metadata >=4.8.0; python_version < '3.10'",
     "typing-extensions >=4.3.0",
     "gymnasium-notices >=0.0.1",
-    "shimmy >=0.1.0,<1.0",
 ]
 dynamic = ["version"]
 

Diff for: tests/envs/test_compatibility.py

@@ -1,12 +1,27 @@
+import re
 from typing import Any, Dict, Optional, Tuple
 
 import numpy as np
+import pytest
 
 import gymnasium
+from gymnasium.error import DependencyNotInstalled
 from gymnasium.spaces import Discrete
 from gymnasium.wrappers.compatibility import EnvCompatibility, LegacyEnv
 
 
+try:
+    import gym
+except ImportError:
+    gym = None
+
+
+try:
+    import shimmy
+except ImportError:
+    shimmy = None
+
+
 class LegacyEnvExplicit(LegacyEnv, gymnasium.Env):
     """Legacy env that explicitly implements the old API."""
 
@@ -125,3 +140,42 @@ def test_make_compatibility_in_make():
     assert img.shape == (1, 1, 3)  # type: ignore
     env.close()
     del gymnasium.envs.registration.registry["LegacyTestEnv-v0"]
+
+
+def test_shimmy_gym_compatibility():
+    assert gymnasium.spec("GymV22Environment-v0") is not None
+    assert gymnasium.spec("GymV26Environment-v0") is not None
+
+    if shimmy is None:
+        with pytest.raises(
+            ImportError,
+            match=re.escape(
+                "To use the gym compatibility environments, run `pip install shimmy[gym]`"
+            ),
+        ):
+            gymnasium.make("GymV22Environment-v0")
+        with pytest.raises(
+            ImportError,
+            match=re.escape(
+                "To use the gym compatibility environments, run `pip install shimmy[gym]`"
+            ),
+        ):
+            gymnasium.make("GymV26Environment-v0")
+    elif gym is None:
+        with pytest.raises(
+            DependencyNotInstalled,
+            match=re.escape(
+                "No module named 'gym' (Hint: You need to install gym with `pip install gym` to use gym environments"
+            ),
+        ):
+            gymnasium.make("GymV22Environment-v0", env_id="CartPole-v1")
+        with pytest.raises(
+            DependencyNotInstalled,
+            match=re.escape(
+                "No module named 'gym' (Hint: You need to install gym with `pip install gym` to use gym environments"
+            ),
+        ):
+            gymnasium.make("GymV26Environment-v0", env_id="CartPole-v1")
+    else:
+        gymnasium.make("GymV22Environment-v0", env_id="CartPole-v1")
+        gymnasium.make("GymV26Environment-v0", env_id="CartPole-v1")

Diff for: tests/envs/test_make.py

@@ -23,6 +23,12 @@
 from tests.wrappers.utils import has_wrapper
 
 
+try:
+    import shimmy
+except ImportError:
+    shimmy = None
+
+
 @pytest.fixture(scope="function")
 def register_make_testing_envs():
     """Registers testing envs for `gym.make`"""

Diff for: tests/envs/utils.py

@@ -14,7 +14,10 @@ def try_make_env(env_spec: EnvSpec) -> Optional[gym.Env]:
     Warning the environments have no wrappers, including time limit and order enforcing.
     """
     # To avoid issues with registered environments during testing, we check that the spec entry points are from gymnasium.envs.
-    if "gymnasium.envs." in env_spec.entry_point:
+    if (
+        isinstance(env_spec.entry_point, str)
+        and "gymnasium.envs." in env_spec.entry_point
+    ):
         try:
             return env_spec.make(disable_env_checker=True).unwrapped
         except (