langchain/retrievers/metal.py/MetalRetriever/__init__
class MetalRetriever:    def __init__(self, client: Any, params: Optional[dict] = None):
        from metal_sdk.metal import Metal

        if not isinstance(client, Metal):
            raise ValueError(
                "Got unexpected client, should be of type metal_sdk.metal.Metal. "
                f"Instead, got {type(client)}"
            )
        self.client: Metal = client
        self.params = params or {}