langchain/chains/qa_with_sources/vector_db.py/VectorDBQAWithSourcesChain/raise_deprecation
class VectorDBQAWithSourcesChain:    def raise_deprecation(cls, values: Dict) -> Dict:
        warnings.warn(
            "`VectorDBQAWithSourcesChain` is deprecated - "
            "please use `from langchain.chains import RetrievalQAWithSourcesChain`"
        )
        return values