langchain/chains/pal/base.py/PALChain/raise_deprecation
class PALChain:    def raise_deprecation(cls, values: Dict) -> Dict:
        if "llm" in values:
            warnings.warn(
                "Directly instantiating an PALChain with an llm is deprecated. "
                "Please instantiate with llm_chain argument or using the one of "
                "the class method constructors from_math_prompt, "
                "from_colored_object_prompt."
            )
            if "llm_chain" not in values and values["llm"] is not None:
                values["llm_chain"] = LLMChain(llm=values["llm"], prompt=MATH_PROMPT)
        return values