langchain/agents/loading.py/_load_agent_from_file
def _load_agent_from_file(
    file: Union[str, Path], **kwargs: Any
) -> BaseSingleActionAgent:
    """Load agent from file."""
    # Convert file to Path object.
    if isinstance(file, str):
        file_path = Path(file)
    else:
        file_path = file
    # Load from either json or yaml.
    if file_path.suffix == ".json":
        with open(file_path) as f:
            config = json.load(f)
    elif file_path.suffix == ".yaml":
        with open(file_path, "r") as f:
            config = yaml.safe_load(f)
    else:
        raise ValueError("File type must be json or yaml")
    # Load the agent from the config now.
    return load_agent_from_config(config, **kwargs)