[Python-Dev] problem with recursive "yield from" delegation

Thu Mar 8 20:00:12 CET 2012

Stefan Behnel, 07.03.2012 21:40:
> I found a problem in the current "yield from" implementation

... and here's another one, also in genobject.c:
"""
int
PyGen_FetchStopIterationValue(PyObject **pvalue) {
 PyObject *et, *ev, *tb;
 PyObject *value = NULL;
 if (PyErr_ExceptionMatches(PyExc_StopIteration)) {
 PyErr_Fetch(&et, &ev, &tb);
 Py_XDECREF(et);
 Py_XDECREF(tb);
 if (ev) {
 value = ((PyStopIterationObject *)ev)->value;
 Py_INCREF(value);
 Py_DECREF(ev);
 }
 } else if (PyErr_Occurred()) {
 return -1;
 }
 if (value == NULL) {
 value = Py_None;
 Py_INCREF(value);
 }
 *pvalue = value;
 return 0;
}
"""
When the StopIteration was set using PyErr_SetObject(), "ev" points to the
value, not the exception instance, so this code lacks exception
normalisation. I use slightly different code in Cython (which needs to be
compatible with Py2.x), but CPython 3.3 could do something along these lines:
"""
 if (ev) {
 if (PyObject_IsInstance(ev, PyExc_StopIteration)) {
 value = ((PyStopIterationObject *)ev)->value;
 Py_INCREF(value); // or maybe XINCREF()?
 Py_DECREF(ev);
 } else {
 /* PyErr_SetObject() puts the value directly into ev */
 value = ev;
 }
 } else ...
"""
Would that be acceptable for CPython as well or would you prefer full
fledged normalisation?
Stefan