langchain/llms/petals.py/Petals/validate_environment
class Petals:    def validate_environment(cls, values: Dict) -> Dict:
        """Validate that api key and python package exists in environment."""
        huggingface_api_key = get_from_dict_or_env(
            values, "huggingface_api_key", "HUGGINGFACE_API_KEY"
        )
        try:
            from petals import DistributedBloomForCausalLM
            from transformers import BloomTokenizerFast

            model_name = values["model_name"]
            values["tokenizer"] = BloomTokenizerFast.from_pretrained(model_name)
            values["client"] = DistributedBloomForCausalLM.from_pretrained(model_name)
            values["huggingface_api_key"] = huggingface_api_key

        except ImportError:
            raise ValueError(
                "Could not import transformers or petals python package."
                "Please install with `pip install -U transformers petals`."
            )
        return values