More examples
-------------

Objects that have a __del__ method

    >>> class Nondestructible(list):
    ...     def __del__(self):
    ...         pass

    >>> x = Nondestructible()
    >>> y = []
    >>> z = []
    >>> x.append(y)
    >>> y.append(z)
    >>> z.append(x)
    >>> del x, y, z

    >>> import objgraph
    >>> objgraph.show_backrefs(objgraph.by_type('Nondestructible'),
    ...                        filename='finalizers.png')
    Graph written to ....dot (3 nodes)
    Image generated as finalizers.png

.. image:: finalizers.png
