langchain/utilities/graphql.py/GraphQLAPIWrapper/validate_environment
class GraphQLAPIWrapper:    def validate_environment(cls, values: Dict) -> Dict:
        """Validate that the python package exists in the environment."""
        try:
            from gql import Client, gql
            from gql.transport.requests import RequestsHTTPTransport
        except ImportError as e:
            raise ImportError(
                "Could not import gql python package. "
                f"Try installing it with `pip install gql`. Received error: {e}"
            )
        headers = values.get("custom_headers")
        transport = RequestsHTTPTransport(
            url=values["graphql_endpoint"],
            headers=headers,
        )
        client = Client(transport=transport, fetch_schema_from_transport=True)
        values["gql_client"] = client
        values["gql_function"] = gql
        return values