def _incr_append(self, key, other):
        with lockutils.lock(key):
            timeout, value = self._get_unlocked(key)

            if value is None:
                return None

            ttl = timeout - timeutils.utcnow_ts()
            new_value = value + other
            self._set_unlocked(key, new_value, ttl)
            return new_value
dataset/ETHPy150Open openstack/neutron/neutron/openstack/common/cache/_backends/memory.py/MemoryBackend._incr_append/swapped operands of `-`