How to use the pypacker.checksum.in_cksum function in pypacker

def test_in_checksum(self):
		print_header("Internet checksum")
		# see packets_dns.py, packet 2
		udp = b"\x00\x35\xa5\xc0\x00\x62\x00\x00\x48\x5b\x81\x80\x00\x01\x00\x03\x00\x00\x00\x01" +\
			b"\x03\x77\x77\x77\x06\x67\x6f\x6f\x67\x6c\x65\x02\x64\x65\x00\x00\x01\x00\x01\xc0" +\
			b"\x0c\x00\x01\x00\x01\x00\x00\x00\x55\x00\x04\xad\xc2\x23\x97\xc0\x0c\x00\x01\x00" +\
			b"\x01\x00\x00\x00\x55\x00\x04\xad\xc2\x23\x98\xc0\x0c\x00\x01\x00\x01\x00\x00\x00" +\
			b"\x55\x00\x04\xad\xc2\x23\x9f\x00\x00\x29\x05\xb4\x00\x00\x00\x00\x00\x00"
		pseudoheader = b"\xc0\xa8\xb2\x01\xc0\xa8\xb2\x16\x00\x11" + struct.pack(">H", len(udp))
		print(len(udp))
		csum = checksum.in_cksum(pseudoheader + udp)
		self.assertEqual(csum, 0x32bf)

def _update_fields(self):
		if self.sum_au_active and self._changed():
			self.sum = 0
			self.sum = checksum.in_cksum(pypacker.Packet.bin(self))

def _update_fields(self):
		# logger.debug("sum is: %d" % self.sum)
		if self.sum_au_active and self._changed():
			# logger.debug("sum is: %d" % self.sum)
			# logger.debug("header: %r", self.header_bytes)
			# logger.debug("body: %r", self.body_bytes)
			self.sum = 0
			self.sum = checksum.in_cksum(self.header_bytes + self.body_bytes)
			# logger.debug("sum is: %d" % self.sum)

def _update_fields(self):
		if self.sum_au_active and self._changed():
			self.sum = 0
			self.sum = checksum.in_cksum(pypacker.Packet.bin(self))

def __str__(self):
		data = "".join(map(str, self.data))
		if not self.sum:
			self.sum = checksum.in_cksum(self.pack_hdr() + data)
		return self.pack_hdr() + data

# we need src/dst for checksum-calculation
			src, dst = self._lower_layer.src, self._lower_layer.dst
		except Exception:
			# not an IP packet as lower layer (src, dst not present) or invalid src/dst
			# logger.debug("could not calculate checksum: %r" % e)
			return

		# pseudoheader
		# packet length = length of upper layers
		self.sum = 0
		# logger.debug("TCP sum recalc: IP6= len(src)=%d\n%s\n%s\nhdr=%s\nbody=%s" %
		#			 (len(src), src, dst, self.header_bytes, self.body_bytes))
		pkt = self.header_bytes + self.body_bytes
		hdr = pack_ipv6_icmp6(src, dst, len(pkt), 58)
		# this will set the header status to changes, should be reset by calling bin()
		self.sum = checksum.in_cksum(hdr + pkt)
		#logger.debug(">>> new checksum: %0X" % self.sum)

def _update_fields(self):
		if self.sum_au_active and self._changed():
			self.sum = 0
			self.sum = checksum.in_cksum(pypacker.Packet.bin(self))