Finalizer objects for Python 2 and Python <= 3.3

util.py

"""Backport weakref.finalize from Python 3.5, simplified."""

import atexit
import sys
import weakref


class finalize(object):
    """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 will be run.
    """

    # Finalizer objects don't have any state of their own.
    # This ensures that they cannot be part of a ref-cycle.
    __slots__ = ()
    _registry = {}

    def __init__(self, obj, func, *args, **kwargs):
        info = functools.partial(func, *args, **kwargs)
        info.weakref = weakref.ref(obj, self)
        self._registry[self] = info

    def __call__(self, wr):
        """Return func(*args, **kwargs) if alive"""
        info = self._registry.pop(self, None)
        if info:
            return info()

    @classmethod
    def _exitfunc(cls):
        if not cls._registry:
            return
        for finalizer in list(cls._registry)
            try:
                finalizer(None)
            except Exception:
                sys.excepthook(*sys.exc_info())
            assert finalizer not in cls._registry

atexit.register(finalize._exitfunc)