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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 _modem_sm(self):
 """Handle modem response state machine."""

        import datetime

        read_timeout = READ_IDLE_TIMEOUT
        while self.ser:
            try:
                resp = self.read(read_timeout)
            except (serial.SerialException, SystemExit, TypeError):
                _LOGGER.debug('Unable to read from port %s', self.port)
                break

            if self.state != self.STATE_IDLE and len(resp) == 0:
                read_timeout = READ_IDLE_TIMEOUT
                self.set_state(self.STATE_IDLE)
                self.incomingcallnotificationfunc(self.state)
                continue

            resp = resp.decode()
            resp = resp.strip('\r\n')
            if self.cmd_response == '':
                self.cmd_responselines.append(resp)
            _LOGGER.debug('mdm: %s', resp)

            if resp in ['OK', 'ERROR']:
                self.cmd_response = resp
                continue

            if resp in ['RING']:
                if self.state == self.STATE_IDLE:
                    self.cid_name = ''
                    self.cid_number = ''
                    self.cid_time = datetime.datetime.now()

                self.set_state(self.STATE_RING)
                self.incomingcallnotificationfunc(self.state)
                read_timeout = READ_RING_TIMOUT
                continue

            if len(resp) <= 4 or resp.find('=') == -1:
                continue

            read_timeout = READ_RING_TIMOUT
            cid_field, cid_data = resp.split('=')
            cid_field = cid_field.strip()
            cid_data = cid_data.strip()
            if cid_field in ['DATE']:
                self.cid_time = datetime.datetime.now()
                continue

            if cid_field in ['NMBR']:
                self.cid_number = cid_data
                continue

            if cid_field in ['NAME']:
                self.cid_name = cid_data
                self.set_state(self.STATE_CALLERID)
                self.incomingcallnotificationfunc(self.state)
                _LOGGER.debug('CID: %s %s %s',
                              self.cid_time.strftime("%I:%M %p"),
                              self.cid_name,
                              self.cid_number)
                try:
                    self.write(self.cmd_callerid)
                except serial.SerialException:
                    _LOGGER.error('Unable to write to port %s', self.port)
                    break

            continue

        self.set_state(self.STATE_FAILED)
        _LOGGER.debug('Exiting modem state machine')
        return