Backport from Py3k branch:

Patch #1591665: implement the __dir__() special function lookup in PyObject_Dir.

Had to change a few bits of the patch because classobjs and __methods__ are still
in Py2.6.

Lib/test/test_builtin.py

@@ -259,12 +259,67 @@ class BuiltinTest(unittest.TestCase):
         self.assertRaises(TypeError, delattr)
 
     def test_dir(self):
-        x = 1
-        self.assert_('x' in dir())
-        import sys
-        self.assert_('modules' in dir(sys))
+        # dir(wrong number of arguments)
         self.assertRaises(TypeError, dir, 42, 42)
 
+        # dir() - local scope
+        local_var = 1
+        self.assert_('local_var' in dir())
+
+        # dir(module)
+        import sys
+        self.assert_('exit' in dir(sys))
+
+        # dir(module_with_invalid__dict__)
+        import types
+        class Foo(types.ModuleType):
+            __dict__ = 8
+        f = Foo("foo")
+        self.assertRaises(TypeError, dir, f)
+
+        # dir(type)
+        self.assert_("strip" in dir(str))
+        self.assert_("__mro__" not in dir(str))
+
+        # dir(obj)
+        class Foo(object):
+            def __init__(self):
+                self.x = 7
+                self.y = 8
+                self.z = 9
+        f = Foo()
+        self.assert_("y" in dir(f))
+
+        # dir(obj_no__dict__)
+        class Foo(object):
+            __slots__ = []
+        f = Foo()
+        self.assert_("__repr__" in dir(f))
+
+        # dir(obj_no__class__with__dict__)
+        # (an ugly trick to cause getattr(f, "__class__") to fail)
+        class Foo(object):
+            __slots__ = ["__class__", "__dict__"]
+            def __init__(self):
+                self.bar = "wow"
+        f = Foo()
+        self.assert_("__repr__" not in dir(f))
+        self.assert_("bar" in dir(f))
+
+        # dir(obj_using __dir__)
+        class Foo(object):
+            def __dir__(self):
+                return ["kan", "ga", "roo"]
+        f = Foo()
+        self.assert_(dir(f) == ["ga", "kan", "roo"])
+
+        # dir(obj__dir__not_list)
+        class Foo(object):
+            def __dir__(self):
+                return 7
+        f = Foo()
+        self.assertRaises(TypeError, dir, f)
+
     def test_divmod(self):
         self.assertEqual(divmod(12, 7), (1, 5))
         self.assertEqual(divmod(-12, 7), (-2, 2))