Index: Lib/unittest/test/test_case.py
===================================================================
--- Lib/unittest/test/test_case.py	(revision 83058)
+++ Lib/unittest/test/test_case.py	(working copy)
@@ -4,6 +4,7 @@
 import sys
 
 from copy import deepcopy
+from collections import deque
 from test import support
 
 import unittest
@@ -460,21 +461,28 @@
         self.assertIn('a', 'abc')
         self.assertIn(2, [1, 2, 3])
         self.assertIn('monkey', animals)
+        self.assertIn(2, deque([1, 2, 3]))
+        self.assertIn(2, {1, 2, 3})
 
         self.assertNotIn('d', 'abc')
         self.assertNotIn(0, [1, 2, 3])
         self.assertNotIn('otter', animals)
+        self.assertNotIn(0, deque([1, 2, 3]))
+        self.assertNotIn(0, {1, 2, 3})
 
         self.assertRaises(self.failureException, self.assertIn, 'x', 'abc')
         self.assertRaises(self.failureException, self.assertIn, 4, [1, 2, 3])
         self.assertRaises(self.failureException, self.assertIn, 'elephant',
                           animals)
+        self.assertRaises(self.failureException, self.assertIn, "x", 123)
 
         self.assertRaises(self.failureException, self.assertNotIn, 'c', 'abc')
         self.assertRaises(self.failureException, self.assertNotIn, 1, [1, 2, 3])
         self.assertRaises(self.failureException, self.assertNotIn, 'cow',
                           animals)
+        self.assertRaises(self.failureException, self.assertNotIn, "x", 123)
 
+
     def testAssertDictContainsSubset(self):
         self.assertDictContainsSubset({}, {})
         self.assertDictContainsSubset({}, {'a': 1})
Index: Lib/unittest/case.py
===================================================================
--- Lib/unittest/case.py	(revision 83058)
+++ Lib/unittest/case.py	(working copy)
@@ -786,9 +786,19 @@
 
         standardMsg = '\n'.join(lines)
         self.fail(self._formatMessage(msg, standardMsg))
+    
+    def _check_in_support(self, obj, msg):
+        """Check that obj supports the `in` operator"""
+        supported = False
+        for attr in ("__contains__", "__iter__", "__getitem__"):
+            supported |= hasattr(obj, attr)
+        if not supported:
+            self.fail(self._formatMessage(msg,
+                            '%s does not support the `in` operator' % obj))
 
     def assertIn(self, member, container, msg=None):
         """Just like self.assertTrue(a in b), but with a nicer default message."""
+        self._check_in_support(container, msg)
         if member not in container:
             standardMsg = '%s not found in %s' % (safe_repr(member),
                                                   safe_repr(container))
@@ -796,6 +806,7 @@
 
     def assertNotIn(self, member, container, msg=None):
         """Just like self.assertTrue(a not in b), but with a nicer default message."""
+        self._check_in_support(container, msg)
         if member in container:
             standardMsg = '%s unexpectedly found in %s' % (safe_repr(member),
                                                         safe_repr(container))