def yes_or_no(question):
    """
            Ask to the user a question. Possible answer y (yes) or n (no)
            :param question: str
            :return: True or False depending on the choice of the user
    """
    while "The answer is invalid":
        reply = str(input(question+' (y/n): ')).lower().strip()
        if reply[:1] == 'y':
            return True
        if reply[:1] == 'n':
            return False