for doc in docs
            ]
            token_count = sum(tokens[:num_docs])
            while token_count > self.max_tokens_limit:
                num_docs -= 1
                token_count -= tokens[num_docs]
        return docs[:num_docs]
    def _get_docs(
        self, inputs: Dict[str, Any], *, run_manager: CallbackManagerForChainRun
    ) -> List[Document]:
        question = inputs[self.question_key]
        docs = self.vectorstore.similarity_search(
            question, k=self.k, **self.search_kwargs
        )
        return self._reduce_tokens_below_limit(docs)
    async def _aget_docs(
        self, inputs: Dict[str, Any], *, run_manager: AsyncCallbackManagerForChainRun
    ) -> List[Document]:
        raise NotImplementedError("VectorDBQAWithSourcesChain does not support async")
    @root_validator()
    def raise_deprecation(cls, values: Dict) -> Dict:
        warnings.warn(
            "`VectorDBQAWithSourcesChain` is deprecated - "
            "please use `from langchain.chains import RetrievalQAWithSourcesChain`"
        )
        return values
    @property
    def _chain_type(self) -> str:
        return "vector_db_qa_with_sources_chain"