langchain/utilities/serpapi.py/SerpAPIWrapper/validate_environment
class SerpAPIWrapper:    def validate_environment(cls, values: Dict) -> Dict:
        """Validate that api key and python package exists in environment."""
        serpapi_api_key = get_from_dict_or_env(
            values, "serpapi_api_key", "SERPAPI_API_KEY"
        )
        values["serpapi_api_key"] = serpapi_api_key
        try:
            from serpapi import GoogleSearch

            values["search_engine"] = GoogleSearch
        except ImportError:
            raise ValueError(
                "Could not import serpapi python package. "
                "Please install it with `pip install google-search-results`."
            )
        return values