python staticmethod and classmethod方法

#https://julien.danjou.info/blog/2013/guide-python-static-class-abstract-methods
class Date:
    def __init__(self,month,day,year):
        self.month = month
        self.day = day
        self.year = year
    def display(self):
        return "parent class {0}-{1}-{2}".format(self.month,self.day,self.year)
    @staticmethod
    def smil(month,day):
        return Date(month,day,2015)

    @classmethod
    def cmil(self,month,day):
        return self(month,day,2015)

class DateSub(Date):
    def display(self):
        return "subclass {0}-{1}-{2}".format(self.month,self.day,self.year)

new_year = Date(1,1,2016)
mi_new_year = Date.smil(1,2)

print(new_year.display())
print(mi_new_year.display())

print(isinstance(new_year,Date))
print(isinstance(mi_new_year,Date))

print("-"*40)
dateSub1=DateSub(10,19,2017)
dateSub2 =DateSub.smil(10,10)
dateSub3 =DateSub.cmil(10,11)
print(dateSub1.display())
print(dateSub2.display())
print(dateSub3.display())

print("isinstance(dateSub1,DateSub) = %s " % isinstance(dateSub1,DateSub))
print("isinstance(dateSub2,DateSub) = %s " % isinstance(dateSub2,DateSub)) #subclass create plain Date object
print("isinstance(dateSub2,Date) = %s " % isinstance(dateSub2,Date))
print("isinstance(dateSub3,DateSub) = %s " % isinstance(dateSub3,DateSub))

print("-"*40)
print Date.display
print Date.smil
print Date.cmil
print Date.cmil(1,1)