def _backup_bytes(target, offset, length):
    """
        Read bytes from one file and write it to a
        backup file with the .bytes_backup suffix
    """
    click.echo('Backup {l} byes at position {offset} on file {file} to .bytes_backup'.format(
        l=length, offset=offset, file=target))

    with open(target, 'r+b') as f:
        f.seek(offset)

        with open(target + '.bytes_backup', 'w+b') as b:
            for _ in xrange(length):
                byte = f.read(1)
                b.write(byte)
            b.flush()

        f.flush()
Read bytes from one file and write it to a
        backup file with the .bytes_backup suffix