code: def set_default_content_type(application, content_type, encoding=None):
      
      settings = get_settings(application, force_instance=True)
      settings.default_content_type = content_type
      settings.default_encoding = encoding
docs: Store the default content type for an application.
  
      :param tornado.web.Application application: the application to modify
      :param str content_type: the content type to default to
      :param str|None encoding: encoding to use when one is unspecified