Il giorno venerdì 10 agosto 2012 11:22:13 UTC+2, Hans Mulder ha scritto:
> On 10/08/12 10:20:00, Giacomo Alzetta wrote:
>
> > I'm trying to implement a c-extension which defines a new
> > class(ModPolynomial on the python side, ModPoly on the C-side).
>
> > At the moment I'm writing the in-place addition, but I get a *really*
> > strange behaviour.
>
> >
>
> > Here's the code for the in-place addition:
>
> >
>
> > #define ModPoly_Check(v) (PyObject_TypeCheck(v, &ModPolyType))
>
> > [...]
>
> > static PyObject *
>
> > ModPoly_InPlaceAdd(PyObject *self, PyObject *other)
>
> > {
>
> >
>
> > if (!ModPoly_Check(self)) {
>
> > // This should never occur for in-place addition, am I correct?
>
> > if (!ModPoly_Check(other)) {
>
> > PyErr_SetString(PyExc_TypeError, "Neither argument is a
> > ModPolynomial.");
>
> > return NULL;
>
> > }
>
> > return ModPoly_InPlaceAdd(other, self);
>
> > } else {
>
> > if (!PyInt_Check(other) && !PyLong_Check(other)) {
>
> > Py_INCREF(Py_NotImplemented);
>
> > return Py_NotImplemented;
>
> > }
>
> > }
>
> >
>
> > ModPoly *Tself = (ModPoly *)self;
>
> > PyObject *tmp, *tmp2;
>
> > tmp = PyNumber_Add(Tself->ob_item[0], other);
>
> > tmp2 = PyNumber_Remainder(tmp, Tself->n_modulus);
>
> >
>
> > Py_DECREF(tmp);
>
> > tmp = Tself->ob_item[0];
>
> > Tself->ob_item[0] = tmp2;
>
> > Py_DECREF(tmp);
>
> >
>
> > printf("%d\n", (int)ModPoly_Check(self));
>
> > return self;
>
> >
>
> > }
>
>
>
> I have no experience writing extensions in C, but as I see it,
>
> you're returning a new reference to self, so you'd need:
>
>
>
> Py_INCREF(self);
>
>
>
> If you don't, then a Py_DECREF inside the assignment operator
>
> causes your polynomial to be garbage collected. Its heap slot
>
> is later used for the unrelated buffer object you're seeing.
>
>
>
> Hope this helps,
>
>
>
> -- HansM
Yes, you're right. I didn't thought the combined operator would do a Py_DECREF
if the iadd operation was implemented, but it obviosuly makes sense.
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