fix station asignment bug

flatland/envs/schedule_generators.py

@@ -70,13 +70,14 @@ def sparse_schedule_generator(speed_ratio_map: Mapping[float, float] = None) ->
         agents_position = []
         agents_target = []
         agents_direction = []
-
+        start_slots = train_stations
+        target_slots = train_stations
         for agent_idx in range(num_agents):
             # Set target for agent
             current_target_node = agent_start_targets_nodes[agent_idx][1]
-            target_station_idx = np.random.randint(len(train_stations[current_target_node]))
-            target = train_stations[current_target_node][target_station_idx]
-            train_stations[current_target_node].pop(target_station_idx)
+            target_station_idx = np.random.randint(len(target_slots[current_target_node]))
+            target = target_slots[current_target_node][target_station_idx]
+            target_slots[current_target_node].pop(target_station_idx)
             agents_target.append((target[0][0], target[0][1]))
 
             # Set start for agent and corresponding orientation
@@ -88,13 +89,12 @@ def sparse_schedule_generator(speed_ratio_map: Mapping[float, float] = None) ->
                 track_to_use = 0
             else:
                 track_to_use = 1
-            for i in range(len(train_stations[current_start_node])):
-                if train_stations[current_start_node][i][1] == track_to_use:
+            for i in range(len(start_slots[current_start_node])):
+                if start_slots[current_start_node][i][1] == track_to_use:
                     start_station_idx = i
                     break
-
-            start = train_stations[current_start_node][start_station_idx]
-            train_stations[current_start_node].pop(start_station_idx)
+            start = start_slots[current_start_node][start_station_idx]
+            start_slots[current_start_node].pop(start_station_idx)
 
             agents_position.append((start[0][0], start[0][1]))
             agents_direction.append(agent_start_orientation)