bpo-30346: An iterator produced by the itertools.groupby() iterator (#1569)

now becames exhausted after advancing the groupby iterator.

1 files changed, 20 insertions, 0 deletions

diff --git a/Lib/test/test_itertools.py b/Lib/test/test_itertools.py
index 50cf148..8353e68 100644
--- a/Lib/test/test_itertools.py
+++ b/Lib/test/test_itertools.py
@@ -751,6 +751,26 @@ class TestBasicOps(unittest.TestCase):
         self.assertEqual(set(keys), expectedkeys)
         self.assertEqual(len(keys), len(expectedkeys))
 
+        # Check case where inner iterator is used after advancing the groupby
+        # iterator
+        s = list(zip('AABBBAAAA', range(9)))
+        it = groupby(s, testR)
+        _, g1 = next(it)
+        _, g2 = next(it)
+        _, g3 = next(it)
+        self.assertEqual(list(g1), [])
+        self.assertEqual(list(g2), [])
+        self.assertEqual(next(g3), ('A', 5))
+        list(it)  # exhaust the groupby iterator
+        self.assertEqual(list(g3), [])
+
+        for proto in range(pickle.HIGHEST_PROTOCOL + 1):
+            it = groupby(s, testR)
+            _, g = next(it)
+            next(it)
+            next(it)
+            self.assertEqual(list(pickle.loads(pickle.dumps(g, proto))), [])
+
         # Exercise pipes and filters style
         s = 'abracadabra'
         # sort s | uniq