Wrapper implementing RAII idiom for ctypes objects.

raii.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import weakref

__all__ = ['CObjectWrapper']


# Keeps a reference to all wrapper instances so that we can dealloc them when
# we need to.
_tracked_refs = {}


def _run_finalizer(ref):
    """Internal weakref callback to run finalizers.
    """
    del _tracked_refs[id(ref)]
    finalizer = ref.finalizer
    wrapped = ref.wrapped
    finalizer(wrapped)


# Must subclass `weakref.ref` so that we can add attributes to it.
class _Ref(weakref.ref):
    pass


class CObjectWrapper(object):
    """C object wrapper using a weakref for memory management.

    Based on `http://code.activestate.com/recipes/577242`.

    :param wrapped: A C object to be wrapped. This will be accessible with
        `self._wrapped`.
    :param finalizer: A callable that takes one argument `wrapped`.
    """
    def __init__(self, wrapped, finalizer):
        self._wrapped = wrapped
        ref = _Ref(self, _run_finalizer)
        ref.wrapped = wrapped
        ref.finalizer = finalizer
        _tracked_refs[id(ref)] = ref