Class finalize

Lib/weakref.py:442–576

Class for finalization of weakrefable objects finalize(obj, func, *args, **kwargs) returns a callable finalizer object which will be called when obj is garbage collected. The first time the finalizer is called it evaluates func(*arg, **kwargs) and returns the result. After this the

class finalize:
    """Class for finalization of weakrefable objects

    finalize(obj, func, *args, **kwargs) returns a callable finalizer
    object which will be called when obj is garbage collected. The
    first time the finalizer is called it evaluates func(*arg, **kwargs)
    and returns the result. After this the finalizer is dead, and
    calling it just returns None.

    When the program exits any remaining finalizers for which the
    atexit attribute is true will be run in reverse order of creation.
    By default atexit is true.
    """

    # Finalizer objects don't have any state of their own.  They are
    # just used as keys to lookup _Info objects in the registry.  This
    # ensures that they cannot be part of a ref-cycle.

    __slots__ = ()
    _registry = {}
    _shutdown = False
    _index_iter = itertools.count()
    _dirty = False
    _registered_with_atexit = False

    class _Info:
        __slots__ = ("weakref", "func", "args", "kwargs", "atexit", "index")

    def __init__(self, obj, func, /, *args, **kwargs):
        if not self._registered_with_atexit:
            # We may register the exit function more than once because
            # of a thread race, but that is harmless
            import atexit
            atexit.register(self._exitfunc)
            finalize._registered_with_atexit = True
        info = self._Info()
        info.weakref = ref(obj, self)
        info.func = func
        info.args = args
        info.kwargs = kwargs or None
        info.atexit = True
        info.index = next(self._index_iter)
        self._registry[self] = info
        finalize._dirty = True

    def __call__(self, _=None):
        """If alive then mark as dead and return func(*args, **kwargs);
        otherwise return None"""
        info = self._registry.pop(self, None)
        if info and not self._shutdown:
            return info.func(*info.args, **(info.kwargs or {}))

    def detach(self):
        """If alive then mark as dead and return (obj, func, args, kwargs);
        otherwise return None"""
        info = self._registry.get(self)
        obj = info and info.weakref()
        if obj is not None and self._registry.pop(self, None):