How to use the tftpy.TftpPacketDAT function in tftpy

def send_dat(self, resend=False):
        """This method reads sends a DAT packet based on what is in self.buffer."""
        if not resend:
            blksize = int(self.options['blksize'])
            self.buffer = self.fileobj.read(blksize)
            logger.debug("Read %d bytes into buffer" % len(self.buffer))
            if self.buffer == "" or self.buffer < blksize:
                logger.info("Reached EOF on file %s" % self.filename)
                self.state.state = 'fin'
            self.blocknumber += 1
            if self.blocknumber > 65535:
                logger.debug("Blocknumber rolled over to zero")
                self.blocknumber = 0
        else:
            logger.warn("Resending block number %d" % self.blocknumber)
        dat = TftpPacketDAT()
        dat.data = self.buffer
        dat.blocknumber = self.blocknumber
        logger.debug("Sending DAT packet %d" % self.blocknumber)
        self.sock.sendto(dat.encode().buffer, (self.host, self.port))
        self.timesent = time.time()

def __init__(self):
        self.classes = {
            1: TftpPacketRRQ,
            2: TftpPacketWRQ,
            3: TftpPacketDAT,
            4: TftpPacketACK,
            5: TftpPacketERR,
            6: TftpPacketOACK
            }

def progresshook(self, pkt):
        if isinstance(pkt, TftpPacketDAT):
            self.progress += len(pkt.data)
            self.out.write("Transferred %d bytes" % self.progress + "\n")
        elif isinstance(pkt, TftpPacketOACK):
            self.out.write("Received OACK, options are: %s" % pkt.options + "\n")

if raddress != self.address:
                logger.warn("Received traffic from %s, expected host %s. Discarding"
                            % (raddress, self.host))
                continue
            if self.port and self.port != rport:
                logger.warn("Received traffic from %s:%s but we're "
                            "connected to %s:%s. Discarding."
                            % (raddress, rport,
                            self.host, self.port))
                continue
            
            if not self.port and self.state.state == 'rrq':
                self.port = rport
                logger.debug("Set remote port for session to %s" % rport)
            
            if isinstance(recvpkt, TftpPacketDAT):
                logger.debug("recvpkt.blocknumber = %d" % recvpkt.blocknumber)
                logger.debug("curblock = %d" % curblock)
                expected_block = curblock + 1
                if expected_block > 65535:
                    logger.debug("block number rollover to 0 again")
                    expected_block = 0
                if recvpkt.blocknumber == expected_block:
                    logger.debug("good, received block %d in sequence" 
                                % recvpkt.blocknumber)
                    curblock = expected_block

                        
                    # ACK the packet, and save the data.
                    logger.info("sending ACK to block %d" % curblock)
                    logger.debug("ip = %s, port = %s" % (self.host, self.port))
                    ackpkt = TftpPacketACK()