Index: Objects/dictobject.c
===================================================================
--- Objects/dictobject.c	(revision 62424)
+++ Objects/dictobject.c	(working copy)
@@ -9,6 +9,7 @@
 
 #include "Python.h"
 
+static PyObject *keyerror_message = NULL;
 
 /* Set a key error with the specified argument, wrapping it in a
  * tuple automatically so that tuple keys are not unpacked as the
@@ -17,7 +18,8 @@
 set_key_error(PyObject *arg)
 {
 	PyObject *tup;
-	tup = PyTuple_Pack(1, arg);
+
+	tup = PyTuple_Pack(2, keyerror_message, arg);
 	if (!tup)
 		return; /* caller will expect error to be set anyway */
 	PyErr_SetObject(PyExc_KeyError, tup);
@@ -233,6 +235,11 @@
 #ifdef SHOW_ALLOC_COUNT
 		Py_AtExit(show_alloc);
 #endif
+
+		/* Also initialize the standard error message */
+		keyerror_message = PyString_FromString("Not in dict");
+		if (keyerror_message == NULL)
+			return NULL;
 	}
 	if (numfree) {
 		mp = free_list[--numfree];
Index: Objects/exceptions.c
===================================================================
--- Objects/exceptions.c	(revision 62424)
+++ Objects/exceptions.c	(working copy)
@@ -1217,17 +1217,26 @@
 static PyObject *
 KeyError_str(PyBaseExceptionObject *self)
 {
-    /* If args is a tuple of exactly one item, apply repr to args[0].
+    /* If args is a tuple of exactly two items, the first is supposed to be a message,
+	   and the second is the offending key.
        This is done so that e.g. the exception raised by {}[''] prints
-         KeyError: ''
+         KeyError: not in dict: ''
        rather than the confusing
          KeyError
-       alone.  The downside is that if KeyError is raised with an explanatory
-       string, that string will be displayed in quotes.  Too bad.
+       alone.
        If args is anything else, use the default BaseException__str__().
     */
-    if (PyTuple_GET_SIZE(self->args) == 1) {
-        return PyObject_Repr(PyTuple_GET_ITEM(self->args, 0));
+    if (PyTuple_GET_SIZE(self->args) == 2) {
+		PyObject *fmt, *ret;
+
+        fmt = PyString_FromString("%s: %r");
+        if (!fmt)
+            return NULL;
+
+        ret = PyString_Format(fmt, self->args);
+
+		Py_DECREF(fmt);
+		return ret;
     }
     return BaseException_str(self);
 }
Index: Objects/setobject.c
===================================================================
--- Objects/setobject.c	(revision 62424)
+++ Objects/setobject.c	(working copy)
@@ -17,7 +17,15 @@
 set_key_error(PyObject *arg)
 {
 	PyObject *tup;
-	tup = PyTuple_Pack(1, arg);
+	static PyObject *message = NULL;
+
+	if (!message) {
+		message = PyString_FromString("Not in set");
+		if (!message)
+			return;
+	}
+
+	tup = PyTuple_Pack(2, message, arg);
 	if (!tup)
 		return; /* caller will expect error to be set anyway */
 	PyErr_SetObject(PyExc_KeyError, tup);
Index: Lib/_abcoll.py
===================================================================
--- Lib/_abcoll.py	(revision 62424)
+++ Lib/_abcoll.py	(working copy)
@@ -256,7 +256,7 @@
     def remove(self, value):
         """Remove an element. If not a member, raise a KeyError."""
         if value not in self:
-            raise KeyError(value)
+            raise KeyError("Not in set", value)
         self.discard(value)
 
     def pop(self):
Index: Lib/weakref.py
===================================================================
--- Lib/weakref.py	(revision 62424)
+++ Lib/weakref.py	(working copy)
@@ -53,7 +53,7 @@
     def __getitem__(self, key):
         o = self.data[key]()
         if o is None:
-            raise KeyError, key
+            raise KeyError("Not in dict", key)
         else:
             return o
 
@@ -151,7 +151,7 @@
                 return args[0]
             raise
         if o is None:
-            raise KeyError, key
+            raise KeyError("Not in dict", key)
         else:
             return o
 
Index: Lib/UserDict.py
===================================================================
--- Lib/UserDict.py	(revision 62424)
+++ Lib/UserDict.py	(working copy)
@@ -19,7 +19,7 @@
             return self.data[key]
         if hasattr(self.__class__, "__missing__"):
             return self.__class__.__missing__(self, key)
-        raise KeyError(key)
+        raise KeyError("Not in dict", key)
     def __setitem__(self, key, item): self.data[key] = item
     def __delitem__(self, key): del self.data[key]
     def clear(self): self.data.clear()
Index: Lib/ConfigParser.py
===================================================================
--- Lib/ConfigParser.py	(revision 62424)
+++ Lib/ConfigParser.py	(working copy)
@@ -588,7 +588,7 @@
                     value = value % vars
                 except KeyError, e:
                     raise InterpolationMissingOptionError(
-                        option, section, rawval, e[0])
+                        option, section, rawval, e.args[-1])
             else:
                 break
         if "%(" in value:
Index: Lib/test/test_dict.py
===================================================================
--- Lib/test/test_dict.py	(revision 62424)
+++ Lib/test/test_dict.py	(working copy)
@@ -450,7 +450,7 @@
         try:
             f[42]
         except KeyError, err:
-            self.assertEqual(err.args, (42,))
+            self.assertEqual(err.args, ("Not in dict", 42))
         else:
             self.fail("f[42] didn't raise KeyError")
         class G(dict):
@@ -459,7 +459,7 @@
         try:
             g[42]
         except KeyError, err:
-            self.assertEqual(err.args, (42,))
+            self.assertEqual(err.args, ("Not in dict", 42))
         else:
             self.fail("g[42] didn't raise KeyError")
 
@@ -469,7 +469,7 @@
         try:
             d[(1,)]
         except KeyError, e:
-            self.assertEqual(e.args, ((1,),))
+            self.assertEqual(e.args, ("Not in dict", (1,)))
         else:
             self.fail("missing KeyError")
 
Index: Lib/test/test_set.py
===================================================================
--- Lib/test/test_set.py	(revision 62424)
+++ Lib/test/test_set.py	(working copy)
@@ -367,7 +367,7 @@
             try:
                 self.s.remove(v1)
             except KeyError, e:
-                v2 = e.args[0]
+                v2 = e.args[1]
                 self.assertEqual(v1, v2)
             else:
                 self.fail()
Index: Lib/test/test_defaultdict.py
===================================================================
--- Lib/test/test_defaultdict.py	(revision 62424)
+++ Lib/test/test_defaultdict.py	(working copy)
@@ -44,7 +44,7 @@
         try:
             d2[15]
         except KeyError, err:
-            self.assertEqual(err.args, (15,))
+            self.assertEqual(err.args, ("Not in dict", 15))
         else:
             self.fail("d2[15] didn't raise KeyError")
         self.assertRaises(TypeError, defaultdict, 1)
@@ -137,7 +137,7 @@
         try:
             d1[(1,)]
         except KeyError, err:
-            self.assertEqual(err.args[0], (1,))
+            self.assertEqual(err.args[1], (1,))
         else:
             self.fail("expected KeyError")
 
Index: Lib/test/test_userdict.py
===================================================================
--- Lib/test/test_userdict.py	(revision 62424)
+++ Lib/test/test_userdict.py	(working copy)
@@ -183,7 +183,7 @@
         try:
             f[42]
         except KeyError, err:
-            self.assertEqual(err.args, (42,))
+            self.assertEqual(err.args, ("Not in dict", 42))
         else:
             self.fail("f[42] didn't raise KeyError")
         class G(UserDict.UserDict):
@@ -192,7 +192,7 @@
         try:
             g[42]
         except KeyError, err:
-            self.assertEqual(err.args, (42,))
+            self.assertEqual(err.args, ("Not in dict", 42))
         else:
             self.fail("g[42] didn't raise KeyError")
 
Index: Modules/_collectionsmodule.c
===================================================================
--- Modules/_collectionsmodule.c	(revision 62424)
+++ Modules/_collectionsmodule.c	(working copy)
@@ -1150,7 +1150,7 @@
 
 PyDoc_STRVAR(defdict_missing_doc,
 "__missing__(key) # Called by __getitem__ for missing key; pseudo-code:\n\
-  if self.default_factory is None: raise KeyError((key,))\n\
+  if self.default_factory is None: raise KeyError('Not in dict', key)\n\
   self[key] = value = self.default_factory()\n\
   return value\n\
 ");
@@ -1162,8 +1162,15 @@
 	PyObject *value;
 	if (factory == NULL || factory == Py_None) {
 		/* XXX Call dict.__missing__(key) */
+		static PyObject *message = NULL;
 		PyObject *tup;
-		tup = PyTuple_Pack(1, key);
+
+		if (!message) {
+		    message = PyString_FromString("Not in dict");
+		    if (!message) return NULL;
+		}
+
+		tup = PyTuple_Pack(2, message, key);
 		if (!tup) return NULL;
 		PyErr_SetObject(PyExc_KeyError, tup);
 		Py_DECREF(tup);