class Service:
    def __init__(self, db, cache):
        self._db = db
        self._cache = cache

    def save(self, k):
        self._db.write(k)

    def load(self, k):
        return self._db.read(k)

    def put(self, k):
        self._cache.set(k)

    def evict(self, k):
        self._cache.drop(k)
