def serialized(self):
        to_ret = {}
        for group, requirements in self.items():
            to_ret[group] = [str(requirement) for requirement in requirements]
        return to_ret
def _get_or_create_cached_value(self, key, getter, ttl=None):
        # happy path
        try:
            expiry, value = self._cache[key]
        except KeyError:
            pass
        else:
            if expiry is None or time.time() < expiry:
                logger.debug("Key %s from cache", key)
                return value
            logger.debug("Cache for key %s has expired", key)

        # get value
        value = getter()
        if ttl:
            expiry = time.time() + ttl
        else:
            expiry = None
        self._cache[key] = (expiry, value)
        logger.debug("Set cache for key %s", key)

        return value