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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _get_state(wallet_name: str) -> _STATE: """ Return current state of revocation registry builder process. :param wallet_name: name of wallet for corresponding Issuer :return: current process state as _STATE enum """


        dir_sentinel = RevRegBuilder.dir_tails_sentinel(wallet_name)
        file_pid = join(dir_sentinel, '.pid')
        file_start = join(dir_sentinel, '.start')
        file_stop = join(dir_sentinel, '.stop')

        if isfile(file_stop):
            return _STATE.STOPPING

        if isfile(file_start) or isfile(file_pid):
            return _STATE.RUNNING

        return _STATE.ABSENT