def ask(prompt: str='', default: str='') -> str:
    """Print the ``prompt``, get user's answer, return it -- or a default."""
    if prompt:
        if default:
            prompt = prompt + ' [' + default + ']'
        prompt = prompt + ' '
    answer = None
    while not answer:
        answer = input(prompt)
        if default and not answer:
            return default
    return answer