weakref 待解决.

暂时不知为何在控制台多执行一次b()后,del a就不会立即销毁Foo实例.

>>> class Foo(object):
    def __init__(self):
        self.obj = None
        print ('created')

    def __del__(self):
        print ('destroyed')

    def show(self):
        print (self.obj)

    def store(self, obj):
        self.obj = obj

>>> import weakref
>>> a = Foo()
created
>>> b = weakref.ref(a)>>> del a
destroyed

>>> a = Foo()
created
>>> b = weakref.ref(a)
>>> b()
<__main__.Foo object at 0x0000000002B025F8>
>>> del a