[Python-3000] Removing __del__

[Jean-Paul Calderone]

On Tue, 19 Sep 2006 23:42:43 +0200, Giovanni Bajo <rasky at develer.com> wrote:
>Michael Chermside <mcherm at mcherm.com> wrote:
>
>> Since we're apparently still in "propose wild ideas" mode for Py3K
>> I'd like to propose that for Py3K we remove __del__. Not "fix" it,
>> not "tweak" it, just remove it and perhaps add a note in the manual
>> pointing people to the weakref module.
>
>
>I don't use __del__ much. I use it only in leaf classes, where it surely can't
>be part of loops. In those rare cases, it's very useful to me. For instance, I
>have a small classes which wraps an existing handle-based C API exported to
>Python. Something along the lines of:
>
>class Wrapper:
>    def __init__(self, *args):
>           self.handle = CAPI.init(*args)
>
>    def __del__(self, *args):
>            CAPI.close(self.handle)
>
>    def foo(self):
>            CAPI.foo(self.handle)
>
>The real class isn't much longer than this (really). How do you propose to
>write this same code without __del__?

Untested, but roughly:

    _weakrefs = []

    def _cleanup(ref, handle):
        _weakrefs.remove(ref)
        CAPI.close(handle)

    class BetterWrapper:
        def __init__(self, *args):
            handle = self.handle = CAPI.init(*args)
            _weakrefs.append(
                weakref.ref(self,
                    lambda ref: _cleanup(ref, handle)))

    def foo(self):
        CAPI.foo(self.handle)

There are probably even better ways too, this is just the first that comes
to mind.

Jean-Paul