_formats = {
    'ymd': '{d.year}-{d.month}-{d.day}',
    'mdy': '{d.month}-{d.day}-{d.year}',
    'dym': '{d.day}-{d.month}-{d.year}'
}

# 通过重写类的__format__方法,我们可以让类在被填充的时候变成任何样子
class Date:
    def __init__(self, year, month, day):
        self.year = year
        self.month = month
        self.day = day

    def __format__(self, code):
        if code == '':
            code = 'ymd'
        fmt = _formats[code]
        return fmt.format(d=self)

d = Date(2024, 11, 11)
format(d)
format(d, 'mdy')

"The Date is {:ymd}".format(d)
"The Date is {:dym}".format(d)