bpo-33462: Add __reversed__ to dict and dict views (GH-6827)

2 files changed, 32 insertions, 0 deletions

diff --git a/Doc/library/stdtypes.rst b/Doc/library/stdtypes.rst
index 4686cec..49d4338 100644
--- a/Doc/library/stdtypes.rst
+++ b/Doc/library/stdtypes.rst
@@ -4285,6 +4285,11 @@ pairs within braces, for example: ``{'jack': 4098, 'sjoerd': 4127}`` or ``{4098:
          LIFO order is now guaranteed. In prior versions, :meth:`popitem` would
          return an arbitrary key/value pair.
 
+   .. describe:: reversed(d)
+
+      Return a reversed iterator over the keys of the dictionary. This is a
+      shortcut for ``reversed(d.keys())``.
+
    .. method:: setdefault(key[, default])
 
       If *key* is in the dictionary, return its value.  If not, insert *key*
@@ -4332,6 +4337,22 @@ pairs within braces, for example: ``{'jack': 4098, 'sjoerd': 4127}`` or ``{4098:
       Dictionary order is guaranteed to be insertion order.  This behavior was
       implementation detail of CPython from 3.6.
 
+   Dictionaries and dictionary views are reversible. ::
+
+      >>> d = {"one": 1, "two": 2, "three": 3, "four": 4}
+      >>> d
+      {'one': 1, 'two': 2, 'three': 3, 'four': 4}
+      >>> list(reversed(d))
+      ['four', 'three', 'two', 'one']
+      >>> list(reversed(d.values()))
+      [4, 3, 2, 1]
+      >>> list(reversed(d.items()))
+      [('four', 4), ('three', 3), ('two', 2), ('one', 1)]
+
+   .. versionchanged:: 3.8
+      Dictionaries are now reversible.
+
+
 .. seealso::
    :class:`types.MappingProxyType` can be used to create a read-only view
    of a :class:`dict`.
@@ -4375,6 +4396,14 @@ support membership tests:
    Return ``True`` if *x* is in the underlying dictionary's keys, values or
    items (in the latter case, *x* should be a ``(key, value)`` tuple).
 
+.. describe:: reversed(dictview)
+
+   Return an reversed iterator over the keys, values or items of the dictionnary.
+   The view will be iterated in reverse order of the insertion.
+
+   .. versionchanged:: 3.8
+      Dictionary views are now reversible.
+
 
 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/Doc/whatsnew/3.8.rst b/Doc/whatsnew/3.8.rst
index 566c369..2d3a116 100644
--- a/Doc/whatsnew/3.8.rst
+++ b/Doc/whatsnew/3.8.rst
@@ -98,6 +98,9 @@ Other Language Changes
 * Added support of ``\N{name}`` escapes in :mod:`regular expressions <re>`.
   (Contributed by Jonathan Eunice and Serhiy Storchaka in :issue:`30688`.)
 
+* Dict and dictviews are now iterable in reversed insertion order using
+  :func:`reversed`. (Contributed by Rémi Lapeyre in :issue:`33462`.)
+
 * The syntax allowed for keyword names in function calls was further
   restricted. In particular, ``f((keyword)=arg)`` is no longer allowed. It was
   never intended to permit more than a bare name on the left-hand side of a