def _set_one_singleton(store: typing.Callable,
item: Item) -> typing.Tuple[str, bool]:
"""Sets item under a key if not already cached.
"""
key, was_cached = item.key, bool(store.setnx(item.key, item.data_as_json))
if was_cached and item.expiration:
store.expire(key, item.expiration)
return key, was_cached
