langchain/llms/huggingface_endpoint.py/HuggingFaceEndpoint/_call
class HuggingFaceEndpoint:    def _call(
        self,
        prompt: str,
        stop: Optional[List[str]] = None,
        run_manager: Optional[CallbackManagerForLLMRun] = None,
    ) -> str:
        """Call out to HuggingFace Hub's inference endpoint.

        Args:
            prompt: The prompt to pass into the model.
            stop: Optional list of stop words to use when generating.

        Returns:
            The string generated by the model.

        Example:
            .. code-block:: python

                response = hf("Tell me a joke.")
        """
        _model_kwargs = self.model_kwargs or {}

        # payload samples
        parameter_payload = {"inputs": prompt, "parameters": _model_kwargs}

        # HTTP headers for authorization
        headers = {
            "Authorization": f"Bearer {self.huggingfacehub_api_token}",
            "Content-Type": "application/json",
        }

        # send request
        try:
            response = requests.post(
                self.endpoint_url, headers=headers, json=parameter_payload
            )
        except requests.exceptions.RequestException as e:  # This is the correct syntax
            raise ValueError(f"Error raised by inference endpoint: {e}")
        generated_text = response.json()
        if "error" in generated_text:
            raise ValueError(
                f"Error raised by inference API: {generated_text['error']}"
            )
        if self.task == "text-generation":
            # Text generation return includes the starter text.
            text = generated_text[0]["generated_text"][len(prompt) :]
        elif self.task == "text2text-generation":
            text = generated_text[0]["generated_text"]
        elif self.task == "summarization":
            text = generated_text[0]["summary_text"]
        else:
            raise ValueError(
                f"Got invalid task {self.task}, "
                f"currently only {VALID_TASKS} are supported"
            )
        if stop is not None:
            # This is a bit hacky, but I can't figure out a better way to enforce
            # stop tokens when making calls to huggingface_hub.
            text = enforce_stop_tokens(text, stop)
        return text