code: def chain_user_names(users, exclude_user, truncate=35):
      
      if not users or not isinstance(exclude_user, get_user_model()):
          return ''
      return truncatechars(
          ', '.join(u'{}'.format(u) for u in users.exclude(pk=exclude_user.pk)),
          truncate)
docs: Tag to return a truncated chain of user names.