<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def request_response(self):
 """Verify that a card is still present and get its operating mode. The Request Response command returns the current operating state of the card. The operating state changes with the authentication process, a card is in Mode 0 after power-up or a Polling command, transitions to Mode 1 with Authentication1, to Mode 2 with Authentication2, and Mode 3 with any of the card issuance commands. The :meth:`request_response` method returns the mode as an integer. Command execution errors raise :exc:`~nfc.tag.TagCommandError`. """

        a, b, e = self.pmm[3] & 7, self.pmm[3] >> 3 & 7, self.pmm[3] >> 6
        timeout = 302E-6 * (b + 1 + a + 1) * 4**e
        data = self.send_cmd_recv_rsp(0x04, '', timeout, check_status=False)
        if len(data) != 1:
            log.debug("insufficient data received from tag")
            raise tt3.Type3TagCommandError(tt3.DATA_SIZE_ERROR)
        return data[0]