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bpo-29942: Fix the use of recursion in itertools.chain.from_iterable. (#911)

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* bpo-29942: Fix the use of recursion in itertools.chain.from_iterable.

Fix the use of recursion in itertools.chain.from_iterable. Using recursion
is unnecessary, and can easily cause stack overflows, especially when
building in low optimization modes or with Py_DEBUG enabled.
(cherry picked from commit 5466d4af5f)
This commit is contained in:
T. Wouters 2017-03-30 12:48:23 -07:00 • committed by GitHub
parent 7b5b1379ac
commit 599bb18103
3 changed files with 39 additions and 24 deletions
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52
Modules/itertoolsmodule.c
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@ -1864,33 +1864,37 @@ chain_next(chainobject *lz)
{
PyObject *item;
if (lz->source == NULL)
return NULL; /* already stopped */
if (lz->active == NULL) {
PyObject *iterable = PyIter_Next(lz->source);
if (iterable == NULL) {
Py_CLEAR(lz->source);
return NULL; /* no more input sources */
}
lz->active = PyObject_GetIter(iterable);
Py_DECREF(iterable);
/* lz->source is the iterator of iterables. If it's NULL, we've already
* consumed them all. lz->active is the current iterator. If it's NULL,
* we should grab a new one from lz->source. */
while (lz->source != NULL) {
if (lz->active == NULL) {
Py_CLEAR(lz->source);
return NULL; /* input not iterable */
PyObject *iterable = PyIter_Next(lz->source);
if (iterable == NULL) {
Py_CLEAR(lz->source);
return NULL; /* no more input sources */
}
lz->active = PyObject_GetIter(iterable);
Py_DECREF(iterable);
if (lz->active == NULL) {
Py_CLEAR(lz->source);
return NULL; /* input not iterable */
}
}
item = (*Py_TYPE(lz->active)->tp_iternext)(lz->active);
if (item != NULL)
return item;
if (PyErr_Occurred()) {
if (PyErr_ExceptionMatches(PyExc_StopIteration))
PyErr_Clear();
else
return NULL; /* input raised an exception */
}
/* lz->active is consumed, try with the next iterable. */
Py_CLEAR(lz->active);
}
item = (*Py_TYPE(lz->active)->tp_iternext)(lz->active);
if (item != NULL)
return item;
if (PyErr_Occurred()) {
if (PyErr_ExceptionMatches(PyExc_StopIteration))
PyErr_Clear();
else
return NULL; /* input raised an exception */
}
Py_CLEAR(lz->active);
return chain_next(lz); /* recurse and use next active */
/* Everything had been consumed already. */
return NULL;
}
static PyObject *