class Rectangle():
       def __init__(self,width,height):
           self.width =width
           self.height=height  

   class CapStr(str):
       def __new__(cls,string):
           string=str.upper(string)
           return str.__new__(cls,string)
   a=CapStr('I will be transfer')
   print(a) #結果 I WILL BE TRANSFER

　　

def __del__(self):
    print('__del__方法被調用了')        
b,c=a,a
c=a
print('del a')
del a
print('del b')
del b
print('del c')
del c #__del__方法被調用了