old_contents: from django.conf.urls.defaults import patterns, url, include
  
  urlpatterns = patterns('',
      url(r'^menu/', include('admin_tools.menu.urls')),
      url(r'^dashboard/', include('admin_tools.dashboard.urls')),
  )
  
new_contents: from django.conf import settings
  from django.conf.urls.defaults import patterns, url, include
  
  urls = []
  if 'admin_tools.menu' in settings.INSTALLED_APPS:
      urls.append(url(r'^menu/', include('admin_tools.menu.urls')))
  if 'admin_tools.dashboard' in settings.INSTALLED_APPS:
      urls.append(url(r'^dashboard/', include('admin_tools.dashboard.urls')))
  
  urlpatterns = patterns('', *urls)
  
subject: build urlpatterns conditionally regarding the content of INSTALLED_APPS