def mac_str_to_bytes(mac_str):
    '''
    Convert a MAC address string into bytes. Works with or without separators:

    b1 = mac_str_to_bytes('08:00:27:13:69:77')
    b2 = mac_str_to_bytes('080027136977')
    assert b1 == b2
    assert isinstance(b1, bytes)
    '''
    if len(mac_str) == 12:
        pass
    elif len(mac_str) == 17:
        sep = mac_str[2]
        mac_str = mac_str.replace(sep, '')
    else:
        raise ValueError('Invalid MAC address')
    chars = (int(mac_str[s:s+2], 16) for s in range(0, 12, 2))
    return bytes(chars) if six.PY3 else b''.join(chr(x) for x in chars)