import sys import struct with open(sys.argv[1], mode='rb') as file: file.read(4) # discard first four bytes rombin = file.read() # read rest of file cksum = 0 for i in struct.unpack('>' + str(len(rombin)/2) + 'H', rombin): cksum += i; cksum &= 0xFFFFFFFF print(hex(cksum))