一、获取某个月的天数
    导入 calendar 模块：
    import calendar

    month_days = calendar.monthrange(1998, 9)
    print(month_days)

    结果：
    F:\PycharmWorkSpace\菜鸟教程，Python实例\venv\Scripts\python.exe F:/Pycharm_WorkSpace/菜鸟教程，Python实例/15计算每个月天数.py
    (1, 30)

    Process finished with exit code 0

    二、获取昨天的日期

    import datetime

    def get_yesterday():
    today = datetime.date.today()
    oneday = datetime.timedelta(days=1)
    yesterday = today - oneday
    return yesterday

    print(get_yesterday())

    结果：
    F:\PycharmWorkSpace\菜鸟教程，Python实例\venv\Scripts\python.exe F:/Pycharm_WorkSpace/菜鸟教程，Python实例/15计算每个月天数.py
    2021-10-02

    Process finished with exit code 0

    datetime.timedelta对象代表两个时间之间的的时间差，两个date或datetime对象相减时可以返回一个timedelta对象。