def _prepare_response_output(
        self,
        response_str: Optional[RESPONSE_TEXT_TYPE],
        source_nodes: List[NodeWithScore],
    ) -> RESPONSE_TYPE:
        """Prepare response object from response string."""
        response_metadata = self._get_metadata_for_response(
            [node_with_score.node for node_with_score in source_nodes]
        )

        if isinstance(self._llm, StructuredLLM):
            # convert string to output_cls
            output = self._llm.output_cls.model_validate_json(str(response_str))
            return PydanticResponse(
                output,
                source_nodes=source_nodes,
                metadata=response_metadata,
            )

        if isinstance(response_str, str):
            return Response(
                response_str,
                source_nodes=source_nodes,
                metadata=response_metadata,
            )
        if isinstance(response_str, Generator):
            return StreamingResponse(
                response_str,
                source_nodes=source_nodes,
                metadata=response_metadata,
            )
        if isinstance(response_str, AsyncGenerator):
            return AsyncStreamingResponse(
                response_str,
                source_nodes=source_nodes,
                metadata=response_metadata,
            )

        if self._output_cls is not None and isinstance(response_str, self._output_cls):
            return PydanticResponse(
                response_str, source_nodes=source_nodes, metadata=response_metadata
            )

        raise ValueError(
            f"Response must be a string or a generator. Found {type(response_str)}"
        )
Prepare response object from response string.
llama-index-core/llama_index/core/response_synthesizers/base.py