Hexdump implementation in Python

hexdump.py

def hexdump(data, addr = 0, num = 0):
    s = ''
    n = 0
    lines = []
    if num == 0: num = len(data)

    if len(data) == 0:
        return '<empty>'

    for i in range(0, num, 16):
        line = ''
        line += '%04x | ' % (addr + i)
        n += 16

        for j in range(n-16, n):
            if j >= len(data): break
            line += '%02x ' % (data[j] & 0xff)

        line += ' ' * (3 * 16 + 7 - len(line)) + ' | '

        for j in range(n-16, n):
            if j >= len(data): break
            c = data[j] if not (data[j] < 0x20 or data[j] > 0x7e) else '.'
            line += '%c' % c

        lines.append(line)
    return '\n'.join(lines)