code: def valid_redditors(redditors, sub):
      
      simplified = list(set(six.text_type(x).lower() for x in redditors))
      return [sub.reddit_session.get_redditor(simplified[i], fetch=False)
              for (i, resp) in enumerate(sub.set_flair_csv(
                  ({'user': x, 'flair_text': x} for x in simplified)))
              if resp['ok']]
docs: Return a verified list of valid Redditor instances.
  
      :param redditors: A list comprised of Redditor instances and/or strings
          that are to be verified as actual redditor accounts.
      :param sub: A Subreddit instance that the authenticated account has
          flair changing permission on.
  
      Note: Flair will be unset for all valid redditors in `redditors` on the
      subreddit `sub`. A valid redditor is defined as a redditor that is
      registered on reddit.