Python C API and references
gagsl-py2 at yahoo.com.ar
Fri Nov 13 13:07:04 CET 2009
En Thu, 12 Nov 2009 06:23:54 -0300, lallous <lallous at lgwm.org> escribió:
> Everytime I use PyObject_SetAttrString(obj, attr_name, py_val) and I
> don't need the reference to py_val I should decrement the reference
> after this call?
If you own a reference to py_val, and you don't need it anymore, you must
decrement it. It doesn't matter if you call PyObject_SetAttrString or
whatever, except when the called function says it "steals" a reference.
> So for example:
> PyObject *py_val = PyInt_FromLong(5)
> PyObject_SetAttrString(py_obj, "val", py_val);
Yes, because PyInt_FromLong returns a new reference, and you own it.
> If so, take sysmodule.c:
> if (PyObject_SetAttrString(builtins, "_", Py_None) != 0)
> return NULL;
> Shouldn't they also call Py_DECREF(Py_None) ?
No, because the reference count of Py_None was not incremented previously;
the code doesn't own a reference to Py_None at that time. It's not the
same as the example above.
> Same logic applies to PyDict_SetItemString() and the reference should be
> decrement after setting the item (ofcourse if the value is not needed).
Yes, same as your first example.
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