Class WeakSequence

lib/sqlalchemy/util/_collections.py:272–298

class WeakSequence(Sequence[_T]):
    def __init__(self, __elements: Sequence[_T] = (), /):
        # adapted from weakref.WeakKeyDictionary, prevent reference
        # cycles in the collection itself
        def _remove(item, selfref=weakref.ref(self)):
            self = selfref()
            if self is not None:
                self._storage.remove(item)

        self._remove = _remove
        self._storage = [
            weakref.ref(element, _remove) for element in __elements
        ]

    def append(self, item):
        self._storage.append(weakref.ref(item, self._remove))

    def __len__(self):
        return len(self._storage)

    def __iter__(self):
        return (
            obj for obj in (ref() for ref in self._storage) if obj is not None
        )

    def __getitem__(self, index):
        return self._storage[index]()


OrderedIdentitySet = IdentitySet