langchain/chains/hyde/base.py/HypotheticalDocumentEmbedder/from_llm
class HypotheticalDocumentEmbedder:    def from_llm(
        cls,
        llm: BaseLanguageModel,
        base_embeddings: Embeddings,
        prompt_key: str,
        **kwargs: Any,
    ) -> HypotheticalDocumentEmbedder:
        """Load and use LLMChain for a specific prompt key."""
        prompt = PROMPT_MAP[prompt_key]
        llm_chain = LLMChain(llm=llm, prompt=prompt)
        return cls(base_embeddings=base_embeddings, llm_chain=llm_chain, **kwargs)