I don't see a way that __del__ could be invoked and access the NULL
between the Py_CLEAR() call and the Py_INCREF() call in the second
version.
On Tue, Aug 5, 2008 at 1:38 PM, Paul Pogonyshev <[EMAIL PROTECTED]> wrote:
> Hi,
>
> Sorry if this topic was discussed before, but I couldn't find.
>
> Py_CLEAR documentation explains why it is better than Py_DECREF and
> NULL assignment. However, I don't understand why there is no similar
> macro for the case you want to replace one object with another?
>
> I.e. 'naive' way:
>
> Py_DECREF (self->x);
> /* This is prone to the same bug Py_CLEAR prevents. */
> self->x = y;
> Py_INCREF (self->x);
>
> Py_CLEAR way:
>
> Py_CLEAR (self->x);
> /* But __del__ can now in principle trigger access to NULL. */
> self->x = y;
> Py_INCREF (self->x);
>
> Way I'd think would be possible:
>
> Py_ASSIGN (self->x, y)
>
> where Py_ASSIGN is defined this way:
>
> #define Py_ASSIGN(op, val) \
> do { \
> PyObject *_py_tmp = (PyObject *)(op); \
> (op) = val; \
> Py_XINCREF(op); \
> Py_XDECREF(_py_tmp); \
> } while (0)
>
> Do I miss something obvious? Or is there already a standard way to
> do that which I overlooked?
>
> Paul
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--
--Guido van Rossum (home page: http://www.python.org/~guido/)
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