def _cache_arp_entry(self, ip, mac, subnet_id, operation):
        arp_entry_tuple = Arp_entry(ip=ip,
                                    mac=mac,
                                    subnet_id=subnet_id,
                                    operation=operation)
        self._pending_arp_set.add(arp_entry_tuple)
:returns: The string path for this Stat.
dataset/ETHPy150Open openstack/neutron/neutron/agent/l3/dvr_local_router.py/DvrLocalRouter._cache_arp_entry--crossover with--dataset/ETHPy150Open pantsbuild/pants/src/python/pants/engine/exp/fs.py/Stat.path