code: def get_url_shortener():
      
      try:
          backend_module = import_module(URL_SHORTENER_BACKEND)
          backend = getattr(backend_module, 'backend')
      except (ImportError, AttributeError):
          warnings.warn('%s backend cannot be imported' % URL_SHORTENER_BACKEND,
                        RuntimeWarning)
          backend = default_backend
      except ImproperlyConfigured as e:
          warnings.warn(str(e), RuntimeWarning)
          backend = default_backend
  
      return backend
docs: Return the selected URL shortener backend.