def _yes_no(question):
    """
    Continuously asks a yes/no question until user input is in [yYnN].
    Returns True or False respectively.
    """
    yesno_map = {'y': True, 'n': False}
    choice = ''
    while choice not in ['y', 'n']:
        choice = input(question).lower()
    return yesno_map[choice]
