How to use the portalocker.constants.LOCK_NB function in portalocker

def __enter__(self):

        current_time = call_time = time.time()
        while call_time + self._timeout > current_time:
            self._lockfile = open(self._filepath, 'w')
            try:
                portalocker.lock(self._lockfile, portalocker.constants.LOCK_NB | portalocker.constants.LOCK_EX)
                return self
            except portalocker.exceptions.LockException:
                pass

            current_time = time.time()
            check_interval = self._check_interval if self._timeout > self._check_interval else self._timeout
            time.sleep(check_interval)

        raise RuntimeError('Timeout was reached')