David Abrahams:
> > So I proxy the bound methods and kill them when p dies.
> I don't quite understand what "proxy the bound methods" means.
Most extension types have a function like this:
PyObject *
MyObject_getattr(MyObject* self,
char * name)
{
/* check for attributes */
...
/* ok, not an attribute, now check the methods
return Py_FindMethod(
MyObject_methods,
(PyObject *) self,
name);
}
Py_FindMethod() returns a PyCFunctionObject. The PyCFunctionObject will
own a reference to the MyObject "self".
Since "self" has a limited lifetime this would be bad. So we could do
this:
PyObject *
MyObject_getattr(MyObject* self,
char * name)
{
/* check for attributes */
...
/* ok, not an attribute, now check the methods
method = Py_FindMethod(
MyObject_methods,
(PyObject *) self,
name);
if (method != NULL) {
add_to_list_of_objects_to_kill(method)
return PyWeakref_NewProxy(method);
}
return NULL;
}
But we can't quite do this because builtin functions are not proxyable.
> So you want a weakrefref. Well, I think this problem can be solved
> by applying the Fundamental Theorem of Software Engineering: apply
> an extra level of indirection.
That's what I do. I was just wondering if there is any reason not to
make C functions weakref/proxyable.
> But Guido's approach of having the wrapper methods check for a null
DOM*
> seems like a reasonable one to me.
It's not unreasonable and it is a bit simpler. But it is more work and
reduces performance slightly in the case where no check need be
performed i.e. the object is owned by Python.
> That's clear to me now. Very interesting thread; thanks for posting
> it here!
Yeah, my first non-stupid post to python-dev.
Cheers,
Brian
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