old_contents: from django.conf.urls import include
  from django.conf.urls import url
  
  from rest_framework import routers
  
  from world.views import CountryViewSet
  from world.views import RegionViewSet
  from world.views import SubregionViewSet
  from world.views import CityViewSet
  from world.views import DistrictViewSet
  
  # Routers provide an easy way of automatically determining the URL conf.
  router = routers.DefaultRouter()
  router.register(r'countries', CountryViewSet)
  router.register(r'regions', RegionViewSet)
  router.register(r'subregions', SubregionViewSet)
  router.register(r'cities', CityViewSet)
  router.register(r'districts', DistrictViewSet)
  
  urlpatterns = [
      url(r'^', include(router.urls)),
      url(r'^v1/', include(router.urls)),
  
      url(r'^v1/countries/(?P<country_id>[0-9]+)/regions/(?P<region_id>[0-9]+)/cities/(?P<city_id>[0-9]+)/districts', DistrictViewSet.as_view({'get': 'list'})),
      url(r'^v1/countries/(?P<country_id>[0-9]+)/regions/(?P<region_id>[0-9]+)/cities', CityViewSet.as_view({'get': 'list'})),
      url(r'^v1/countries/(?P<country_id>[0-9]+)/regions/(?P<region_id>[0-9]+)/subregions', SubregionViewSet.as_view({'get': 'list'})),
      url(r'^v1/countries/(?P<country_id>[0-9]+)/regions', RegionViewSet.as_view({'get': 'list'})),
  ]
  
new_contents: from django.conf.urls import include
  from django.conf.urls import url
  from django.contrib.staticfiles.urls import staticfiles_urlpatterns
  
  from rest_framework import routers
  
  from world.views import CountryViewSet
  from world.views import RegionViewSet
  from world.views import SubregionViewSet
  from world.views import CityViewSet
  from world.views import DistrictViewSet
  
  # Routers provide an easy way of automatically determining the URL conf.
  router = routers.DefaultRouter()
  router.register(r'countries', CountryViewSet)
  router.register(r'regions', RegionViewSet)
  router.register(r'subregions', SubregionViewSet)
  router.register(r'cities', CityViewSet)
  router.register(r'districts', DistrictViewSet)
  
  urlpatterns = [
      url(r'^', include(router.urls)),
      url(r'^v1/', include(router.urls)),
  
      url(r'^v1/countries/(?P<country_id>[0-9]+)/regions/(?P<region_id>[0-9]+)/cities/(?P<city_id>[0-9]+)/districts', DistrictViewSet.as_view({'get': 'list'})),
      url(r'^v1/countries/(?P<country_id>[0-9]+)/regions/(?P<region_id>[0-9]+)/cities', CityViewSet.as_view({'get': 'list'})),
      url(r'^v1/countries/(?P<country_id>[0-9]+)/regions/(?P<region_id>[0-9]+)/subregions', SubregionViewSet.as_view({'get': 'list'})),
      url(r'^v1/countries/(?P<country_id>[0-9]+)/regions', RegionViewSet.as_view({'get': 'list'})),
  ]
  urlpatterns += staticfiles_urlpatterns()
  
subject: add static file url pattern