langchain/chains/llm.py/LLMChain/from_string
class LLMChain:    def from_string(cls, llm: BaseLanguageModel, template: str) -> Chain:
        """Create LLMChain from LLM and template."""
        prompt_template = PromptTemplate.from_template(template)
        return cls(llm=llm, prompt=prompt_template)