langchain/prompts/chat.py/BaseStringMessagePromptTemplate/from_template_file
class BaseStringMessagePromptTemplate:    def from_template_file(
        cls: Type[MessagePromptTemplateT],
        template_file: Union[str, Path],
        input_variables: List[str],
        **kwargs: Any,
    ) -> MessagePromptTemplateT:
        prompt = PromptTemplate.from_file(template_file, input_variables)
        return cls(prompt=prompt, **kwargs)