bpo-36650: Fix handling of empty keyword args in C version of lru_cache. (GH-12881)

Lib/test/test_functools.py

@@ -1271,6 +1271,20 @@ class TestLRU:
         self.assertEqual(f(20), '.20.')
         self.assertEqual(f.cache_info().currsize, 10)
 
+    def test_lru_bug_36650(self):
+        # C version of lru_cache was treating a call with an empty **kwargs
+        # dictionary as being distinct from a call with no keywords at all.
+        # This did not result in an incorrect answer, but it did trigger
+        # an unexpected cache miss.
+
+        @self.module.lru_cache()
+        def f(x):
+            pass
+
+        f(0)
+        f(0, **{})
+        self.assertEqual(f.cache_info().hits, 1)
+
     def test_lru_hash_only_once(self):
         # To protect against weird reentrancy bugs and to improve
         # efficiency when faced with slow __hash__ methods, the