langchain/llms/openai.py/BaseOpenAI/prep_streaming_params
class BaseOpenAI:    def prep_streaming_params(self, stop: Optional[List[str]] = None) -> Dict[str, Any]:
        """Prepare the params for streaming."""
        params = self._invocation_params
        if "best_of" in params and params["best_of"] != 1:
            raise ValueError("OpenAI only supports best_of == 1 for streaming")
        if stop is not None:
            if "stop" in params:
                raise ValueError("`stop` found in both the input and default params.")
            params["stop"] = stop
        params["stream"] = True
        return params