12. 解决方案：文档

练习解决方案：readable_timedelta

下面是文档字符串的一种编写方式！

def readable_timedelta(days):
    """Print the number of weeks and days in a number of days."""
    weeks = days // 7
    remainder = days % 7
    return "{} week(s) and {} day(s)".format(weeks, remainder)