code: def _generate_session_id(self):
          
  
          while True:
              rand = os.urandom(16)
              now = time.time()
              secret_key = self._config.secret_key
              session_id = hashlib.sha1(("%s%s%s%s" % (rand, now, utils.safestr(web.ctx.ip), secret_key)).encode("utf-8"))
              session_id = session_id.hexdigest()
              if session_id not in self.store:
                  break
          return session_id
docs: Generate a random id for session