关于 langChain 的使用问题？

Question

我用亚马逊云的Lambda函数，通过langChain调用OpenAI API。我把OPENAI_API_KEY存在了Lambda函数的环境变量里了。神奇的是，在创建new ChatOpenAI（）实例的时候没有传入OPENAI_API_KEY，还是可以获取到正确的返回值。这是为什么？

import { ChatOpenAI } from "langchain/chat_models/openai";
import { HumanChatMessage, SystemChatMessage } from "langchain/schema";

export const handler = async (event) => {
  const chat = new ChatOpenAI({ temperature: 0 });
  const response = await chat.call([
    new HumanChatMessage(
      "把大象装冰箱一共分几步？"
    ),
    new HumanChatMessage(
      "为什么？"
    ),
  ]);

  return response;
};

Answer 1

已解决。经过验证langChain会自动读取环境变量。文档也有说明，没仔细看。
Here we create a chat model using the API key stored in the environment variable OPENAI_API_KEY or AZURE_OPENAI_API_KEY in case you are using Azure OpenAI. We'll be calling this chat model throughout this section.