old_contents: from django.conf import settings
  
  class BaseEngine(object):
      """
      BaseEngine interface
      """
      
      @staticmethod
      def is_engine_available(name):
          return name in settings.INSTALLED_APPS
  
      @staticmethod
      def factory(name):
          
          engine_name = name.lower()
          
          if engine_name == "mongodb":
              if BaseEngine.is_engine_available(engine_name):
                  return MongoDB()
              else:
                  raise NotImplementedError()
  
          assert 0, "Bad Engine Type: " + name
  
      
      def url(self):
          raise NotImplementedError()
new_contents: from django.conf import settings
  
  class BaseEngine(object):
      """
      BaseEngine interface
      """
      
      @staticmethod
      def is_engine_available(name):
          return name in settings.INSTALLED_APPS
  
      @staticmethod
      def factory(name):
          
          engine_name = name.lower()
          
          # TODO: import Engines dynamically
          if engine_name == "mongodb":
              if BaseEngine.is_engine_available(engine_name):
                  from mongodb import MongoDB
                  return MongoDB()
              else:
                  raise NotImplementedError()
  
          assert 0, "Bad Engine Type: " + name
  
      
      def url(self):
          raise NotImplementedError()
subject: fix import