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一、__format__

• 自定制格式化字符串

date_dic = {    'ymd': '{0.year}:{0.month}:{0.day}',    'dmy': '{0.day}/{0.month}/{0.year}',    'mdy': '{0.month}-{0.day}-{0.year}',}class Date:    def __init__(self, year, month, day):        self.year = year        self.month = month        self.day = day    def __format__(self, format_spec):        # 默认打印ymd的{0.year}:{0.month}:{0.day}格式        if not format_spec or format_spec not in date_dic:            format_spec = 'ymd'        fmt = date_dic[format_spec]        return fmt.format(self)d1 = Date(2016, 12, 29)

print(format(d1))

2016:12:29

print('{:mdy}'.format(d1))

12-29-2016