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gh-101892: Fix SystemError when a callable iterator call exhausts the iterator #101896

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Mar 4, 2023
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25 changes: 25 additions & 0 deletions Lib/test/test_iter.py
Original file line number Diff line number Diff line change
Expand Up @@ -348,6 +348,31 @@ def spam(state=[0]):
return i
self.check_iterator(iter(spam, 20), list(range(10)), pickle=False)

def test_iter_function_concealing_reentrant_exhaustion(self):
# gh-101892: Test two-argument iter() with a function that
# exhausts its associated iterator but forgets to either return
# a sentinel value or raise StopIteration.
HAS_MORE = 1
NO_MORE = 2

def exhaust(iterator):
"""Exhaust an iterator without raising StopIteration."""
list(iterator)

def spam():
# Touching the iterator with exhaust() below will call
# spam() once again so protect against recursion.
if spam.is_recursive_call:
return NO_MORE
spam.is_recursive_call = True
exhaust(spam.iterator)
return HAS_MORE

spam.is_recursive_call = False
spam.iterator = iter(spam, NO_MORE)
with self.assertRaises(StopIteration):
next(spam.iterator)

# Test exception propagation through function iterator
def test_exception_function(self):
def spam(state=[0]):
Expand Down
Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Callable iterators no longer raise :class:`SystemError` when the
callable object exhausts the iterator but forgets to either return a
sentinel value or raise :class:`StopIteration`.
4 changes: 2 additions & 2 deletions Objects/iterobject.c
Original file line number Diff line number Diff line change
Expand Up @@ -219,15 +219,14 @@ calliter_iternext(calliterobject *it)
}

result = _PyObject_CallNoArgs(it->it_callable);
if (result != NULL) {
if (result != NULL && it->it_sentinel != NULL){
int ok;

ok = PyObject_RichCompareBool(it->it_sentinel, result, Py_EQ);
if (ok == 0) {
return result; /* Common case, fast path */
}

Py_DECREF(result);
if (ok > 0) {
Py_CLEAR(it->it_callable);
Py_CLEAR(it->it_sentinel);
Expand All @@ -238,6 +237,7 @@ calliter_iternext(calliterobject *it)
Py_CLEAR(it->it_callable);
Py_CLEAR(it->it_sentinel);
}
Py_XDECREF(result);
return NULL;
}

Expand Down