code: def lookup_url(self, url):
          
          if type(url) is not str:
              url = url.encode('utf8')
          if not url.strip():
              raise ValueError("Empty input string.")
          url_hashes = URL(url).hashes
          try:
              list_names = self._lookup_hashes(url_hashes)
              self.storage.commit()
          except Exception:
              self.storage.rollback()
              raise
          if list_names:
              return list_names
          return None
docs: Look up specified URL in Safe Browsing threat lists.