diff -r 4daffae06f64 -r 54b4712f2933 Include/dictobject.h
--- a/Include/dictobject.h	Fri Jan 08 01:03:03 2016 -0800
+++ b/Include/dictobject.h	Sat Jan 09 03:16:58 2016 +0100
@@ -23,6 +23,7 @@ typedef struct _dictkeysobject PyDictKey
 typedef struct {
     PyObject_HEAD
     Py_ssize_t ma_used;
+    size_t ma_version;
     PyDictKeysObject *ma_keys;
     PyObject **ma_values;
 } PyDictObject;
diff -r 4daffae06f64 -r 54b4712f2933 Objects/dictobject.c
--- a/Objects/dictobject.c	Fri Jan 08 01:03:03 2016 -0800
+++ b/Objects/dictobject.c	Sat Jan 09 03:16:58 2016 +0100
@@ -69,6 +69,7 @@ to the combined-table form.
 #include "Python.h"
 #include "dict-common.h"
 #include "stringlib/eq.h"
+#include "structmember.h"

 /*[clinic input]
 class dict "PyDictObject *" "&PyDict_Type"
@@ -188,6 +189,11 @@ static PyObject _dummy_struct;

 #define dummy (&_dummy_struct)

+/* FIXME: handle integer overflow: never use value 0.
+   The version 0 is reserved for "missing key". */
+#define DICT_INC_VERSION(mp) \
+    do { ((PyDictObject *)(mp))->ma_version++; } while (0)
+
 #ifdef Py_REF_DEBUG
 PyObject *
 _PyDict_Dummy(void)
@@ -383,6 +389,7 @@ new_dict(PyDictKeysObject *keys, PyObjec
     mp->ma_keys = keys;
     mp->ma_values = values;
     mp->ma_used = 0;
+    mp->ma_version = 0;
     return (PyObject *)mp;
 }

@@ -802,13 +809,19 @@ insertdict(PyDictObject *mp, PyObject *k
     assert(PyUnicode_CheckExact(key) || mp->ma_keys->dk_lookup == lookdict);
     Py_INCREF(value);
     MAINTAIN_TRACKING(mp, key, value);
+
     old_value = *value_addr;
     if (old_value != NULL) {
         assert(ep->me_key != NULL && ep->me_key != dummy);
         *value_addr = value;
+        if (value != old_value) {
+            DICT_INC_VERSION(mp);
+        }
         Py_DECREF(old_value); /* which **CAN** re-enter (see issue #22653) */
     }
     else {
+        DICT_INC_VERSION(mp);
+
         if (ep->me_key == NULL) {
             Py_INCREF(key);
             if (mp->ma_keys->dk_usable <= 0) {
@@ -1280,6 +1293,8 @@ PyDict_DelItem(PyObject *op, PyObject *k
         _PyErr_SetKeyError(key);
         return -1;
     }
+
+    DICT_INC_VERSION(mp);
     old_value = *value_addr;
     *value_addr = NULL;
     mp->ma_used--;
@@ -1350,6 +1365,7 @@ PyDict_Clear(PyObject *op)
     mp->ma_keys = Py_EMPTY_KEYS;
     mp->ma_values = empty_values;
     mp->ma_used = 0;
+    DICT_INC_VERSION(mp);
     /* ...then clear the keys and values */
     if (oldvalues != NULL) {
         n = DK_SIZE(oldkeys);
@@ -1483,8 +1499,11 @@ PyObject *
         _PyErr_SetKeyError(key);
         return NULL;
     }
+
     *value_addr = NULL;
+    DICT_INC_VERSION(mp);
     mp->ma_used--;
+
     if (!_PyDict_HasSplitTable(mp)) {
         ENSURE_ALLOWS_DELETIONS(mp);
         old_key = ep->me_key;
@@ -2417,6 +2436,7 @@ PyDict_SetDefault(PyObject *d, PyObject
         val = defaultobj;
         mp->ma_keys->dk_usable--;
         mp->ma_used++;
+        DICT_INC_VERSION(mp);
     }
     return val;
 }
@@ -2515,6 +2535,7 @@ dict_popitem(PyDictObject *mp)
     Py_INCREF(dummy);
     ep->me_key = dummy;
     ep->me_value = NULL;
+    DICT_INC_VERSION(mp);
     mp->ma_used--;
     assert(mp->ma_keys->dk_entries[0].me_value == NULL);
     mp->ma_keys->dk_entries[0].me_hash = i + 1;  /* next place to start */
@@ -2720,6 +2741,7 @@ dict_new(PyTypeObject *type, PyObject *a
         _PyObject_GC_UNTRACK(d);

     d->ma_used = 0;
+    d->ma_version = 0;
     d->ma_keys = new_keys_object(PyDict_MINSIZE_COMBINED);
     if (d->ma_keys == NULL) {
         Py_DECREF(self);
@@ -2740,6 +2762,12 @@ dict_iter(PyDictObject *dict)
     return dictiter_new(dict, &PyDictIterKey_Type);
 }

+static PyMemberDef mapp_memberlist[] = {
+    {"__version__", T_ULONG, offsetof(PyDictObject, ma_version), READONLY,
+     "dictionary object"},
+    {NULL}      /* Sentinel */
+};
+
 PyDoc_STRVAR(dictionary_doc,
 "dict() -> new empty dictionary\n"
 "dict(mapping) -> new dictionary initialized from a mapping object's\n"
@@ -2781,7 +2809,7 @@ PyTypeObject PyDict_Type = {
     (getiterfunc)dict_iter,                     /* tp_iter */
     0,                                          /* tp_iternext */
     mapp_methods,                               /* tp_methods */
-    0,                                          /* tp_members */
+    mapp_memberlist,                            /* tp_members */
     0,                                          /* tp_getset */
     0,                                          /* tp_base */
     0,                                          /* tp_dict */