langchain/retrievers/databerry.py/DataberryRetriever/__init__
class DataberryRetriever:    def __init__(
        self,
        datastore_url: str,
        top_k: Optional[int] = None,
        api_key: Optional[str] = None,
    ):
        self.datastore_url = datastore_url
        self.api_key = api_key
        self.top_k = top_k