Compare two disk images and emit CSV file listing bit-position differences

cmpdisks.py

#!/usr/bin/env python
#
# Compare two disk images for bit differences.
# Usage:  ./cmpdisks.py diskA.dsk diskB.dsk
#
# Tom Moertel <tmoertel@gmail.com>
# 2012-04-29

import sys

def main(file_a, file_b):
    sa, sb = map(file_to_bytestream, (file_a, file_b))
    for (byte_posn, (ca, cb)) in enumerate(zip(sa, sb)):
        if ca != cb:
            mask = 1
            for bit in xrange(8):
                cabit = ca & mask
                cbbit = cb & mask
                if cabit != cbbit:
                    print "%d,%d,%d,%d" % (byte_posn, bit, cabit, cbbit)
                mask <<= 1

def file_to_bytestream(file_name):
    with file(file_name, 'rb') as f:
        return map(ord, f.read())

if __name__ == '__main__':
    main(*sys.argv[1:3])