old_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 ContinentViewSet
  from world.views import CurrencyViewSet
  from world.views import ExtraCountryViewSet
  
  # Routers provide an easy way of automatically determining the URL conf.
  router = routers.DefaultRouter()
  
  countries = ExtraCountryViewSet.as_view({'get': 'list'})
  country_detail = ExtraCountryViewSet.as_view({'get': 'retrieve'})
  
  router.register(r'countries', ExtraCountryViewSet)
  router.register(r'continents', ContinentViewSet)
  router.register(r'currencies', CurrencyViewSet)
  
  urlpatterns = [
      url(r'^', include(router.urls)),
      url(r'^v1/', include(router.urls)),
  
      url(r'^countries/$', countries, name='country-list'),
      url(r'^countries/(?P<pk>[0-9]+)/$', country_detail, name='country-detail'),
  ]
  urlpatterns += staticfiles_urlpatterns()
  
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 ContinentViewSet
  from world.views import CurrencyViewSet
  from world.views import ExtraCountryViewSet
  
  # Routers provide an easy way of automatically determining the URL conf.
  router = routers.DefaultRouter()
  
  countries = ExtraCountryViewSet.as_view({'get': 'list'})
  country_detail = ExtraCountryViewSet.as_view({'get': 'retrieve'})
  
  router.register(r'countries', ExtraCountryViewSet)
  router.register(r'continents', ContinentViewSet)
  router.register(r'currencies', CurrencyViewSet)
  
  urlpatterns = [
      url(r'^', include(router.urls)),
      url(r'^v1/', include(router.urls)),
  ]
  urlpatterns += staticfiles_urlpatterns()
  
subject: Remove unnecessary urls in router