bpo-29942: Fix the use of recursion in itertools.chain.from_iterable. (#913)
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 5466d4af5fe76ec0a5fbc8a05675287d9e8e9d14)
diff --git a/Lib/test/test_itertools.py b/Lib/test/test_itertools.py
index 5672104..7b2362d 100644
--- a/Lib/test/test_itertools.py
+++ b/Lib/test/test_itertools.py
@@ -1465,6 +1465,14 @@
self.assertRaises(AssertionError, list, cycle(gen1()))
self.assertEqual(hist, [0,1])
+ def test_long_chain_of_empty_iterables(self):
+ # Make sure itertools.chain doesn't run into recursion limits when
+ # dealing with long chains of empty iterables. Even with a high
+ # number this would probably only fail in Py_DEBUG mode.
+ it = chain.from_iterable(() for unused in xrange(10000000))
+ with self.assertRaises(StopIteration):
+ next(it)
+
class SubclassWithKwargsTest(unittest.TestCase):
def test_keywords_in_subclass(self):
# count is not subclassable...