def _unpack_ipv4(ip_str):
    if not ip_str.lower().startswith('0000:0000:0000:0000:0000:ffff:'):
        return None

    return ip_str.rsplit(':', 1)[1]
Unpack an IPv4 address that was mapped in a compressed IPv6 address.
dataset/ETHPy150Open django/django/django/utils/ipv6.py/_unpack_ipv4