On Nov 12, 9:23 am, "lallous" <lall...@lgwm.org> wrote: > Hello, > > 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?
Not necessarily: it depends where py_val came from. I find the 'ownership' model described in the docs quite helpful: http://docs.python.org/c-api/intro.html#reference-count-details It's probably better to read the docs, but here's a short version: If you create a reference to some Python object in a function in your code, you then 'own' that reference, and you're responsible for getting rid of it by the time the function exits. There are various ways this can happen: you can return the reference, thereby transferring ownership to the calling function; you can explicitly discard the reference by calling Py_DECREF; or you can transfer ownership by calling a function that 'steals' the reference (most functions in the C-API don't steal references, but rather borrow them for the duration of the function call). > > So for example: > > PyObject *py_val = PyInt_FromLong(5) > PyObject_SetAttrString(py_obj, "val", py_val); > Py_DECREF(py_val) > > Right? Yes. Here you've created the reference in the first place, so you should Py_DECREF it before you exit. Right after the PyObject_SetAttrString call is a good place to do this. > > If so, take sysmodule.c: > > if (PyObject_SetAttrString(builtins, "_", Py_None) != 0) > return NULL; > > Shouldn't they also call Py_DECREF(Py_None) ? No, I don't think so. I assume you're looking at the sys_displayhook function? This function doesn't create new references to Py_None (well, except when it's about to return Py_None to the caller), so at this point it doesn't own any reference to Py_None: it's not responsible for decrementing the reference count. > Same logic applies to PyDict_SetItemString() Yes. -- Mark -- http://mail.python.org/mailman/listinfo/python-list
