类例4

#firstclass.pyclass firstclass:    def setdata(self,value):        self.data=value    def display(self):        print(self.data)if __name__=='__main__':    x=firstclass()    y=firstclass()    x.setdata("myname")    y.setdata(3.566)    x.display()    y.display()secondclass.pyfrom firstclass import firstclassclass secondclass(firstclass):    def display(self):        print('current value=%s'%self.data)if __name__=='__main__':    z=secondclass()    z.setdata(42)    z.display()#thirdclass.pyfrom secondclass import secondclassclass thirdclass(secondclass):    def __init__(self,value):#实例化对象时会自动调用该方法        self.data=value    def __add__(self,other):        return thirdclass(self.data+other)    def __str__(self):        return '[thirdclass:%s]'%self.data    def mul(self,other):        self.data*=otherif __name__=='__main__':    a=thirdclass('abc')    '''a.display()    print(a)      #打印实例对象    b=a+'xyz'     #调用__add__    b.display()    print("b:",b)    a.mul(3)    print(a)'''    print(a.__dict__) #查看实例a的属性    print(thirdclass.__dict__)#查看类的属性    print(a.__class__)#查看实例所属的类    print(thirdclass.__class__)