python · sweeneyde · Jun 7, 2020 · Jun 7, 2020 · Jun 7, 2020 · Jun 7, 2020
diff --git a/Doc/library/stdtypes.rst b/Doc/library/stdtypes.rst
@@ -4622,6 +4622,11 @@ support membership tests:
    .. versionchanged:: 3.8
       Dictionary views are now reversible.
 
+.. describe:: dictview.mapping
+
+   Return the dictionary the view refers to.  If ``d`` is a
+   dictionary, then ``d is d.keys().mapping``, ``d is d.values().mapping``,
+   and ``d is d.items().mapping``.
 
 Keys views are set-like since their entries are unique and hashable.  If all
 values are hashable, so that ``(key, value)`` pairs are unique and hashable,

diff --git a/Lib/test/test_dict.py b/Lib/test/test_dict.py
@@ -105,6 +105,19 @@ def test_items(self):
         self.assertRaises(TypeError, d.items, None)
         self.assertEqual(repr(dict(a=1).items()), "dict_items([('a', 1)])")
 
+    def test_views_mapping(self):
+        d = {}
+        self.assertIs(d.keys().mapping, d)
+        self.assertIs(d.items().mapping, d)
+        self.assertIs(d.values().mapping, d)
+
+        class MyDict(dict):
+            pass
+        my_dict = MyDict()
+        self.assertIs(my_dict.keys().mapping, my_dict)
+        self.assertIs(my_dict.items().mapping, my_dict)
+        self.assertIs(my_dict.values().mapping, my_dict)
+
     def test_contains(self):
         d = {}
         self.assertNotIn('a', d)

diff --git a/Misc/NEWS.d/next/Core and Builtins/2020-06-07-08-58-42.bpo-40890.pXK3wX.rst b/Misc/NEWS.d/next/Core and Builtins/2020-06-07-08-58-42.bpo-40890.pXK3wX.rst
@@ -0,0 +1 @@
+Each dictionary view now has a ``mapping`` attribute that references the original dictionary.  Patch contributed by Dennis Sweeney.
diff --git a/Objects/dictobject.c b/Objects/dictobject.c
@@ -117,6 +117,7 @@ converting the dict to the combined table.
 #include "pycore_pystate.h"  // _PyThreadState_GET()
 #include "dict-common.h"
 #include "stringlib/eq.h"    // unicode_eq()
+#include "structmember.h"    // PyMemberDef
 
 /*[clinic input]
 class dict "PyDictObject *" "&PyDict_Type"
@@ -4448,6 +4449,12 @@ static PyNumberMethods dictviews_as_number = {
     (binaryfunc)dictviews_or,           /*nb_or*/
 };
 
+static PyMemberDef dictview_members[] = {
+    {"mapping", T_OBJECT, offsetof(_PyDictViewObject, dv_dict),
+     READONLY, "dictionary that this view refers to"},
+    {NULL} /* Sentinel */
+};
+
 static PyObject*
 dictviews_isdisjoint(PyObject *self, PyObject *other)
 {
@@ -4545,7 +4552,7 @@ PyTypeObject PyDictKeys_Type = {
     (getiterfunc)dictkeys_iter,                 /* tp_iter */
     0,                                          /* tp_iternext */
     dictkeys_methods,                           /* tp_methods */
-    0,
+    .tp_members = dictview_members,
 };
 
 static PyObject *
@@ -4651,7 +4658,7 @@ PyTypeObject PyDictItems_Type = {
     (getiterfunc)dictitems_iter,                /* tp_iter */
     0,                                          /* tp_iternext */
     dictitems_methods,                          /* tp_methods */
-    0,
+    .tp_members = dictview_members,
 };
 
 static PyObject *
@@ -4732,7 +4739,7 @@ PyTypeObject PyDictValues_Type = {
     (getiterfunc)dictvalues_iter,               /* tp_iter */
     0,                                          /* tp_iternext */
     dictvalues_methods,                         /* tp_methods */
-    0,
+    .tp_members = dictview_members,
 };
 
 static PyObject *
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		Each dictionary view now has a ``mapping`` attribute that references the original dictionary. Patch contributed by Dennis Sweeney.