def setdefault(self, key, value):
        """Sets the key value to `value` if it doesn't exist

        :params key: Item key as string.
        :type key: `unicode string`
        :params value: Value to assign to the key. This can be anything that
          is handled by the current backend.
        """
        try:
            return self[key]
        except __HOLE__:
            self[key] = value
            return value
dataset/ETHPy150Open openstack/neutron/neutron/openstack/common/cache/backends.py/BaseCache.setdefault