code: def get_renderer(app, id):
      
      renderer = app.extensions.get('nav_renderers', {})[id]
  
      if isinstance(renderer, tuple):
          mod_name, cls_name = renderer
          mod = import_module(mod_name)
  
          cls = mod
          for name in cls_name.split('.'):
              cls = getattr(cls, name)
  
          return cls
  
      return renderer
docs: Retrieve a renderer.
  
      :param app: :class:`~flask.Flask` application to look ``id`` up on
      :param id: Internal renderer id-string to look up