1 files changed, 20 insertions, 3 deletions
diff --git a/Lib/test/test_dict.py b/Lib/test/test_dict.py
index 3104cbc66cb..69f1a098920 100644
--- a/Lib/test/test_dict.py
+++ b/Lib/test/test_dict.py
@@ -338,17 +338,34 @@ class DictTest(unittest.TestCase):
         self.assertRaises(Exc, baddict2.fromkeys, [1])
 
         # test fast path for dictionary inputs
+        res = dict(zip(range(6), [0]*6))
         d = dict(zip(range(6), range(6)))
-        self.assertEqual(dict.fromkeys(d, 0), dict(zip(range(6), [0]*6)))
-
+        self.assertEqual(dict.fromkeys(d, 0), res)
+        # test fast path for set inputs
+        d = set(range(6))
+        self.assertEqual(dict.fromkeys(d, 0), res)
+        # test slow path for other iterable inputs
+        d = list(range(6))
+        self.assertEqual(dict.fromkeys(d, 0), res)
+
+        # test fast path when object's constructor returns large non-empty dict
         class baddict3(dict):
             def __new__(cls):
                 return d
-        d = {i : i for i in range(10)}
+        d = {i : i for i in range(1000)}
         res = d.copy()
         res.update(a=None, b=None, c=None)
         self.assertEqual(baddict3.fromkeys({"a", "b", "c"}), res)
 
+        # test slow path when object is a proper subclass of dict
+        class baddict4(dict):
+            def __init__(self):
+                dict.__init__(self, d)
+        d = {i : i for i in range(1000)}
+        res = d.copy()
+        res.update(a=None, b=None, c=None)
+        self.assertEqual(baddict4.fromkeys({"a", "b", "c"}), res)
+
     def test_copy(self):
         d = {1: 1, 2: 2, 3: 3}
         self.assertIsNot(d.copy(), d)