python关键日期计算

在coding的过程中有时候会需要用到一些特殊日期，比如说是一个月的最后一天的日期，昨天的日期等等。

    def first_day_of_next_month(self, old_date):
        old_date = datetime.datetime.strptime(old_date, "%Y-%m-%d")
        next_month = old_date.replace(day=28) + datetime.timedelta(days=4)
        next_month = next_month.replace(day=1)
        return next_month.strftime("%Y-%m-%d")
    
    def last_day_of_month(self, any_day):
        any_day = datetime.datetime.strptime(any_day, "%Y-%m-%d")
        next_month = any_day.replace(day=28) + datetime.timedelta(days=4)  # this will never fail
        return (next_month - datetime.timedelta(days=next_month.day)).strftime("%Y-%m-%d")

    def get_last_day(self, current_date):
        current_date = datetime.datetime.strptime(current_date, "%Y-%m-%d")
        last_date = current_date + datetime.timedelta(days=1)
        return last_date.strftime("%Y-%m-%d")