def in6_6to4ExtractAddr(addr):
    """
    Extract IPv4 address embbeded in 6to4 address. Passed address must be
    a 6to4 addrees. None is returned on error.
    """
    try:
        addr = inet_pton(socket.AF_INET6, addr)
    except:
        return None
    if addr[:2] != b" \x02":
        return None
    return inet_ntop(socket.AF_INET, addr[2:6])
Extract IPv4 address embbeded in 6to4 address. Passed address must be
    a 6to4 addrees. None is returned on error.