code: def unique_slug(queryset, slug_field, slug):
      
      i = 0
      while True:
          if i > 0:
              if i > 1:
                  slug = slug.rsplit("-", 1)[0]
              slug = "%s-%s" % (slug, i)
          try:
              queryset.get(**{slug_field: slug})
          except ObjectDoesNotExist:
              break
          i += 1
      return slug
docs: Ensures a slug is unique for the given queryset, appending
      an integer to its end until the slug is unique.