Question

I have a class that stores all created references in a static list like this:

class A:
    _List = []

    def __init__(self):
        A._List.append(self)

    def __del__(self):
        A._List.remove(self)

Now if I do the following:

a = A()
del a

a is not deleted, since it is still referenced to in the list. But the reference would be destroyed if the destructor would be called. Is there a way to somehow force python to execute the __del__ method anyway, so that it can get removed from the static list?

Answer 1

You can use weakref.WeakValueDictionary (or weakref.WeakKeyDictionary), it would automatcally remove any elements that do not exist anymore:

class A(object):
    _instances = weakref.WeakValueDictionary()
    _next_id = functools.partial(next, itertools.count())

    def __init__(self):
        self._instances[self._next_id()] = self