Fix pickling error. (#2100)

CHANGELOG.md

@@ -14,6 +14,7 @@ Copy and pasting the git commit messages is __NOT__ enough.
 ### Deprecated
 ### Fixed
 - Fixed issue where `SumoTrafficSimulation` could get locked up on reset if a scenario had only 1 map but multiple scenario variations.
+- Fixed an issue where an out-of-scope method reference caused a pickling error.
 ### Removed
 ### Security
 

envision/client_config.py

@@ -36,6 +36,10 @@ class SingleAttributeOverride(NamedTuple):
     """The maximum number of elements an iterable attribute can contain."""
 
 
+def _default_override():
+    return SingleAttributeOverride(True, None)
+
+
 @dataclass(frozen=True)
 class EnvisionStateFilter:
     """A state filtering tool."""
@@ -49,7 +53,4 @@ class EnvisionStateFilter:
     def default(cls):
         """Give a new default filter."""
 
-        def default_override():
-            return SingleAttributeOverride(True, None)
-
-        return cls(defaultdict(default_override), defaultdict(default_override))
+        return cls(defaultdict(_default_override), defaultdict(_default_override))

envision/tests/test_data_replay.py

@@ -42,11 +42,13 @@
 TIMESTEP_SEC = 0.1
 
 
+class KeepLaneAgent(Agent):
+    def act(self, obs):
+        return "keep_lane"
+
+
 @pytest.fixture
 def agent_spec():
-    class KeepLaneAgent(Agent):
-        def act(self, obs):
-            return "keep_lane"
 
     return AgentSpec(
         interface=AgentInterface.from_type(