python之format

format_dict={
    'ymd':'{0.year} {0.month} {0.day}',
    'y-m-d':'{0.year}-{0.month}-{0.day}',
    'm:d:y':'{0.month}:{0.day}:{0.year}'
}
class time:
    def __init__(self,year,month,day):
        self.year=year
        self.month=month
        self.day=day
    def __format__(self,item):
        if not item or item not in format_dict:
            item='ymd'
        return format_dict[item].format(self)

f=time(2020,2,23)
print(format(f,'y:m:t'))