Forwards all np_random assignments to the actual environment and prevent access to the _np_random in wrappers (#2857)

Author: pseudo-rnd-thoughts

gym/core.py

@@ -315,6 +315,21 @@ def metadata(self) -> dict:
     def metadata(self, value):
         self._metadata = value
 
+    @property
+    def np_random(self) -> RandomNumberGenerator:
+        """Returns the environment np_random."""
+        return self.env.np_random
+
+    @np_random.setter
+    def np_random(self, value):
+        self.env.np_random = value
+
+    @property
+    def _np_random(self):
+        raise AttributeError(
+            "Can't access `_np_random` of a wrapper, use `.unwrapped._np_random` or `.np_random`."
+        )
+
     def step(self, action: ActType) -> Tuple[ObsType, float, bool, dict]:
         """Steps through the environment with action."""
         return self.env.step(action)