docs: def format_pkg_list(packages, versions_as_list, attr):
      '''
      Formats packages according to parameters for list_pkgs.
      '''
      ret = copy.deepcopy(packages)
      if attr:
          requested_attr = {'epoch', 'version', 'release', 'arch', 'install_date', 'install_date_time_t'}
  
          if attr != 'all':
              requested_attr &= set(attr + ['version'])
  
          for name in ret:
              versions = []
              for all_attr in ret[name]:
                  filtered_attr = {}
                  for key in requested_attr:
                      if all_attr[key]:
                          filtered_attr[key] = all_attr[key]
                  versions.append(filtered_attr)
              ret[name] = versions
          return ret
  
      for name in ret:
          ret[name] = [format_version(d['epoch'], d['version'], d['release'])
                       for d in ret[name]]
      if not versions_as_list:
          stringify(ret)
      return ret