langchain/document_loaders/blockchain.py/BlockchainDocumentLoader/__init__
class BlockchainDocumentLoader:    def __init__(
        self,
        contract_address: str,
        blockchainType: BlockchainType = BlockchainType.ETH_MAINNET,
        api_key: str = "docs-demo",
        startToken: str = "",
        get_all_tokens: bool = False,
        max_execution_time: Optional[int] = None,
    ):
        self.contract_address = contract_address
        self.blockchainType = blockchainType.value
        self.api_key = os.environ.get("ALCHEMY_API_KEY") or api_key
        self.startToken = startToken
        self.get_all_tokens = get_all_tokens
        self.max_execution_time = max_execution_time

        if not self.api_key:
            raise ValueError("Alchemy API key not provided.")

        if not re.match(r"^0x[a-fA-F0-9]{40}$", self.contract_address):
            raise ValueError(f"Invalid contract address {self.contract_address}")