langchain/utilities/duckduckgo_search.py/DuckDuckGoSearchAPIWrapper/validate_environment
class DuckDuckGoSearchAPIWrapper:    def validate_environment(cls, values: Dict) -> Dict:
        """Validate that python package exists in environment."""
        try:
            from duckduckgo_search import ddg  # noqa: F401
        except ImportError:
            raise ValueError(
                "Could not import duckduckgo-search python package. "
                "Please install it with `pip install duckduckgo-search`."
            )
        return values