bpo-31179: Make dict.copy() up to 5.5 times faster. (#3067)

1 files changed, 48 insertions, 2 deletions

diff --git a/Lib/test/test_dict.py b/Lib/test/test_dict.py
index 4386eda..aa149d3 100644
--- a/Lib/test/test_dict.py
+++ b/Lib/test/test_dict.py
@@ -271,11 +271,57 @@ class DictTest(unittest.TestCase):
         self.assertEqual(baddict3.fromkeys({"a", "b", "c"}), res)
 
     def test_copy(self):
-        d = {1:1, 2:2, 3:3}
-        self.assertEqual(d.copy(), {1:1, 2:2, 3:3})
+        d = {1: 1, 2: 2, 3: 3}
+        self.assertIsNot(d.copy(), d)
+        self.assertEqual(d.copy(), d)
+        self.assertEqual(d.copy(), {1: 1, 2: 2, 3: 3})
+
+        copy = d.copy()
+        d[4] = 4
+        self.assertNotEqual(copy, d)
+
         self.assertEqual({}.copy(), {})
         self.assertRaises(TypeError, d.copy, None)
 
+    def test_copy_fuzz(self):
+        for dict_size in [10, 100, 1000, 10000, 100000]:
+            dict_size = random.randrange(
+                dict_size // 2, dict_size + dict_size // 2)
+            with self.subTest(dict_size=dict_size):
+                d = {}
+                for i in range(dict_size):
+                    d[i] = i
+
+                d2 = d.copy()
+                self.assertIsNot(d2, d)
+                self.assertEqual(d, d2)
+                d2['key'] = 'value'
+                self.assertNotEqual(d, d2)
+                self.assertEqual(len(d2), len(d) + 1)
+
+    def test_copy_maintains_tracking(self):
+        class A:
+            pass
+
+        key = A()
+
+        for d in ({}, {'a': 1}, {key: 'val'}):
+            d2 = d.copy()
+            self.assertEqual(gc.is_tracked(d), gc.is_tracked(d2))
+
+    def test_copy_noncompact(self):
+        # Dicts don't compact themselves on del/pop operations.
+        # Copy will use a slow merging strategy that produces
+        # a compacted copy when roughly 33% of dict is a non-used
+        # keys-space (to optimize memory footprint).
+        # In this test we want to hit the slow/compacting
+        # branch of dict.copy() and make sure it works OK.
+        d = {k: k for k in range(1000)}
+        for k in range(950):
+            del d[k]
+        d2 = d.copy()
+        self.assertEqual(d2, d)
+
     def test_get(self):
         d = {}
         self.assertIs(d.get('c'), None)