How to use the safety.app_settings.IP_RESOLVER function in safety

def location(request):
    """
    Transform an IP address into an approximate location.
    """
    ip = utils.resolve(app_settings.IP_RESOLVER, request)

    try:
        location = GeoIP() and GeoIP().city(ip)
    except:
        # Handle 127.0.0.1 and not found IPs
        return ugettext('unknown')

    if location and location['country_name']:
        if location['city']:
            return '%s, %s' % (location['city'], location['country_name'])
        else:
            return location['country_name']

    return ugettext('unknown')

def create_session(self, request, user):
        ip = utils.resolve(app_settings.IP_RESOLVER, request)
        device = utils.resolve(app_settings.DEVICE_RESOLVER, request)
        location = utils.resolve(app_settings.LOCATION_RESOLVER, request)

        user_agent = request.META.get('HTTP_USER_AGENT', '')
        user_agent = user_agent[:200] if user_agent else user_agent

        try:
            with transaction.atomic():
                obj = self.create(
                    user=user,
                    session_key=request.session.session_key,
                    ip=ip,
                    user_agent=user_agent,
                    device=device,
                    location=location,
                    expiration_date=request.session.get_expiry_date(),