langchain/cache.py/MomentoCache/__init__
class MomentoCache:    def __init__(
        self,
        cache_client: momento.CacheClient,
        cache_name: str,
        *,
        ttl: Optional[timedelta] = None,
        ensure_cache_exists: bool = True,
    ):
        """Instantiate a prompt cache using Momento as a backend.

        Note: to instantiate the cache client passed to MomentoCache,
        you must have a Momento account. See https://gomomento.com/.

        Args:
            cache_client (CacheClient): The Momento cache client.
            cache_name (str): The name of the cache to use to store the data.
            ttl (Optional[timedelta], optional): The time to live for the cache items.
                Defaults to None, ie use the client default TTL.
            ensure_cache_exists (bool, optional): Create the cache if it doesn't
                exist. Defaults to True.

        Raises:
            ImportError: Momento python package is not installed.
            TypeError: cache_client is not of type momento.CacheClientObject
            ValueError: ttl is non-null and non-negative
        """
        try:
            from momento import CacheClient
        except ImportError:
            raise ImportError(
                "Could not import momento python package. "
                "Please install it with `pip install momento`."
            )
        if not isinstance(cache_client, CacheClient):
            raise TypeError("cache_client must be a momento.CacheClient object.")
        _validate_ttl(ttl)
        if ensure_cache_exists:
            _ensure_cache_exists(cache_client, cache_name)

        self.cache_client = cache_client
        self.cache_name = cache_name
        self.ttl = ttl