66 shortest-path-predictor: cleanup and unit test; not working yet

flatland/envs/predictions.py

@@ -133,6 +133,8 @@ class ShortestPathPredictorForRailEnv(PredictionBuilder):
                 # Take shortest possible path
                 cell_transitions = self.env.rail.get_transitions((*agent.position, agent.direction))
 
+                new_position = None
+                new_direction = None
                 if np.sum(cell_transitions) == 1:
                     new_direction = np.argmax(cell_transitions)
                     new_position = get_new_position(agent.position, new_direction)
@@ -148,21 +150,21 @@ class ShortestPathPredictorForRailEnv(PredictionBuilder):
                 else:
                     raise Exception("No transition possible {}".format(cell_transitions))
 
-
+                # which action to take for the transition?
                 action = None
                 for _action in [RailEnvActions.MOVE_FORWARD, RailEnvActions.MOVE_RIGHT, RailEnvActions.MOVE_LEFT]:
-                    cell_isFree, new_cell_isValid, new_direction, _new_position, transition_isValid = \
-                        self.env._check_action_on_agent(action, agent)
+                    _, _, _new_direction, _new_position, _ = self.env._check_action_on_agent(_action, agent)
                     if np.array_equal(_new_position, new_position):
                         action = _action
                         break
                 assert action is not None
+
+                # update the agent's position and direction
                 agent.position = new_position
                 agent.direction = new_direction
+
+                # prediction is ready
                 prediction[index] = [index, *new_position, new_direction, action]
-                action_done = True
-                if not action_done:
-                    raise Exception("Cannot move further. Something is wrong")
             prediction_dict[agent.handle] = prediction
 
             # cleanup: reset initial position