[Python-Dev] UNREF invalid object

[Gustavo Niemeyer]

> It's not just more elegant, it's mandatory.  If you look at the expansion of
> Py_DECREF, you'll find that it does all sorts of (necessary) things under
> different build types.  In particular, under a debug build, calling
> PyObject_Del() fails to unlink the object from the doubly-linked list of all
> objects, and that's exactly the cause of an "UNREF invalid object" error.
> Py_DECREF() instead arranges to call _Py_ForgetReference(), which (among
> other things) does the unlinking in a debug build.  You *could* call all
> that stuff yourself by hand, but then you'd need as much #ifdef pain as goes
> into the expansion of Py_DECREF in order to get it all right.

Hummm... I thought PyObject_Del could be safely used when the object was
"private". Ok, I'll investigate what Py_DECREF really does, and why it
breaks if PyObject_Del is used.

> > OTOH, I wouldn't like to get over the problem without knowing what's
> > really happening.  Is this a common problem pattern?
> 
> Nope.  Everyone else <wink>

Ok.. I should have asked "is this something obviously stupid?" instead.

:-))

> calls PyObject_Del only on the "self" argument to the type's
> tp_dealloc function (which is called *by* the expansion of
> Py_DECREF(self), so self must not be subjected to a Py_DECREF again).
> Everything else should go thru Py_DECREF, including contained objects.

This paragraph looks like a good documentation to put somewhere.

Thanks for explaining.

-- 
Gustavo Niemeyer

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