GPS checksum validation using Python

gps_cheksum.py

def chksum(inp): # GPS message checksum verification
	if not inp.startswith("$"): return False
	if not inp[-3:].startswith("*"): return False
	payload = inp[1:-3]
	checksum = 0
	for i in xrange(len(payload)):
		checksum =  checksum ^ ord(payload[i])
	return ("%02X" % checksum) == inp[-2:]

# do simple test
line = "$GPVTG,,T,,M,0.129,N,0.239,K,D*24"
print "Checksum correct:", chksum(line)