langchain/llms/base.py/BaseLLM/__call__
class BaseLLM:    def __call__(
        self, prompt: str, stop: Optional[List[str]] = None, callbacks: Callbacks = None
    ) -> str:
        """Check Cache and run the LLM on the given prompt and input."""
        if not isinstance(prompt, str):
            raise ValueError(
                "Argument `prompt` is expected to be a string. Instead found "
                f"{type(prompt)}. If you want to run the LLM on multiple prompts, use "
                "`generate` instead."
            )
        return (
            self.generate([prompt], stop=stop, callbacks=callbacks)
            .generations[0][0]
            .text
        )