code: def list_archivers(config):
      
      root = pathlib.Path(config.cache_path)
      result = []
      for name in ALL_ARCHIVERS.keys():
          if (root / name).exists():
              result.append(name)
      return result
docs: List the names of archivers with data.
  
      :param config: The configuration
      :type  config: :class:`wily.config.WilyConfig`
  
      :return: A list of archiver names
      :rtype: ``list`` of ``str``