fixing level generation and stability

flatland/envs/rail_generators.py

@@ -678,8 +678,8 @@ def sparse_rail_generator(num_cities=5, num_intersections=4, num_trainstations=2
         if num_cities > 1:
             train_stations = [[] for i in range(num_cities)]
             built_num_trainstation = 0
-            spot_found = True
             for station in range(num_trainstations):
+                spot_found = True
                 trainstation_node = int(station / num_trainstations * num_cities)
 
                 station_x = np.clip(node_positions[trainstation_node][0] + np.random.randint(-node_radius, node_radius),
@@ -705,7 +705,7 @@ def sparse_rail_generator(num_cities=5, num_intersections=4, num_trainstations=2
                     if tries > 100:
                         warnings.warn("Could not set trainstations, please change initial parameters!!!!")
                         spot_found = False
-                        break
+
                 if spot_found:
                     train_stations[trainstation_node].append((station_x, station_y))
 
@@ -714,13 +714,12 @@ def sparse_rail_generator(num_cities=5, num_intersections=4, num_trainstations=2
                                                 (station_x, station_y))
                 # Check if connection was made
                 if len(connection) == 0:
-                    if len(train_stations) > 0:
+                    if len(train_stations[trainstation_node]) > 0:
                         train_stations[trainstation_node].pop(-1)
                 else:
                     built_num_trainstation += 1
 
         # Adjust the number of agents if you could not build enough trainstations
-
         if num_agents > built_num_trainstation:
             num_agents = built_num_trainstation
             warnings.warn("sparse_rail_generator: num_agents > nr_start_goal, changing num_agents")