bpo-40890: Add `mapping` property to dict views (GH-20749)

2 files changed, 17 insertions, 0 deletions

diff --git a/Doc/library/stdtypes.rst b/Doc/library/stdtypes.rst
index 2082b84..7028d24 100644
--- a/Doc/library/stdtypes.rst
+++ b/Doc/library/stdtypes.rst
@@ -4622,6 +4622,12 @@ support membership tests:
    .. versionchanged:: 3.8
       Dictionary views are now reversible.
 
+.. describe:: dictview.mapping
+
+   Return a :class:`types.MappingProxyType` that wraps the original
+   dictionary to which the view refers.
+
+   .. versionadded:: 3.10
 
 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,
@@ -4661,6 +4667,12 @@ An example of dictionary view usage::
    >>> keys ^ {'sausage', 'juice'}
    {'juice', 'sausage', 'bacon', 'spam'}
 
+   >>> # get back a read-only proxy for the original dictionary
+   >>> values.mapping
+   mappingproxy({'eggs': 2, 'sausage': 1, 'bacon': 1, 'spam': 500})
+   >>> values.mapping['spam']
+   500
+
 
 .. _typecontextmanager:
 
diff --git a/Doc/whatsnew/3.10.rst b/Doc/whatsnew/3.10.rst
index 1234b2e..629909b 100644
--- a/Doc/whatsnew/3.10.rst
+++ b/Doc/whatsnew/3.10.rst
@@ -74,6 +74,11 @@ New Features
   number of ones in the binary expansion of a given integer, also known
   as the population count. (Contributed by Niklas Fiekas in :issue:`29882`.)
 
+* The views returned by :meth:`dict.keys`, :meth:`dict.values` and
+  :meth:`dict.items` now all have a ``mapping`` attribute that gives a
+  :class:`types.MappingProxyType` object wrapping the original
+  dictionary. (Contributed by Dennis Sweeney in :issue:`40890`.)
+
 
 Other Language Changes
 ======================