langchain/llms/openai.py/OpenAIChat/validate_environment
class OpenAIChat:    def validate_environment(cls, values: Dict) -> Dict:
        """Validate that api key and python package exists in environment."""
        openai_api_key = get_from_dict_or_env(
            values, "openai_api_key", "OPENAI_API_KEY"
        )
        openai_api_base = get_from_dict_or_env(
            values,
            "openai_api_base",
            "OPENAI_API_BASE",
            default="",
        )
        openai_proxy = get_from_dict_or_env(
            values,
            "openai_proxy",
            "OPENAI_PROXY",
            default="",
        )
        openai_organization = get_from_dict_or_env(
            values, "openai_organization", "OPENAI_ORGANIZATION", default=""
        )
        try:
            import openai

            openai.api_key = openai_api_key
            if openai_api_base:
                openai.api_base = openai_api_base
            if openai_organization:
                openai.organization = openai_organization
            if openai_proxy:
                openai.proxy = {"http": openai_proxy, "https": openai_proxy}  # type: ignore[assignment]  # noqa: E501
        except ImportError:
            raise ImportError(
                "Could not import openai python package. "
                "Please install it with `pip install openai`."
            )
        try:
            values["client"] = openai.ChatCompletion
        except AttributeError:
            raise ValueError(
                "`openai` has no `ChatCompletion` attribute, this is likely "
                "due to an old version of the openai package. Try upgrading it "
                "with `pip install --upgrade openai`."
            )
        warnings.warn(
            "You are trying to use a chat model. This way of initializing it is "
            "no longer supported. Instead, please use: "
            "`from langchain.chat_models import ChatOpenAI`"
        )
        return values