Index: django/core/cache/backends/base.py
===================================================================
--- django/core/cache/backends/base.py	(revision 5023)
+++ django/core/cache/backends/base.py	(working copy)
@@ -54,3 +54,6 @@
         Returns True if the key is in the cache and has not expired.
         """
         return self.get(key) is not None
+
+    # Allow use of 'in' operator.
+    __contains__ = has_key
Index: tests/regressiontests/cache/tests.py
===================================================================
--- tests/regressiontests/cache/tests.py	(revision 5023)
+++ tests/regressiontests/cache/tests.py	(working copy)
@@ -46,6 +46,11 @@
         self.assertEqual(cache.has_key("hello"), True)
         self.assertEqual(cache.has_key("goodbye"), False)
 
+    def test_in(self): 
+        cache.set("hello", "goodbye") 
+        self.assertEqual("hello" in cache, True) 
+        self.assertEqual("goodbye" in cache, False) 
+
     def test_data_types(self):
         # test data types
         stuff = {