def METHOD_NAME(self):
    if self._dirty:
        # See if we need to remove any old entries
        for slug in list(self.backups.keys()):
            data = self.backups[slug].get(KEY_LAST_SEEN)
            if data is not None and self._time.now() > self._time.parse(data) + timedelta(days=CACHE_EXPIRATION_DAYS):
                del self.backups[slug]
        self.save()