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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 _req(self, req):
 """Send command and wait for response. The command will be repeated 3 times at most in case data loss of serial port. Args: req (str):
 Command to send, please do not include new line in the end. Returns: [str]: The output lines """

        logger.debug('DUT> %s', req)
        self._log and self.pause()
        times = 3
        res = None

        while times:
            times = times - 1
            try:
                self._sendline(req)
                self._expect(req)

                line = None
                res = []

                while True:
                    line = self._readline()
                    logger.debug('Got line %s', line)

                    if line == 'Done':
                        break

                    if line:
                        res.append(line)
                break

            except:
                logger.exception('Failed to send command')
                self.close()
                self._init()

        self._log and self.resume()
        return res