From: Georg Brandl <georg@python.org>
Date: Sun, 6 Jan 2008 16:17:56 +0000 (+0000)
Subject: #1582: document __reversed__, patch by Mark Russell.
X-Git-Tag: v2.6a1~713
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=81de0d24d589251d9465b3a214a9b9adb3962f4a;p=python

#1582: document __reversed__, patch by Mark Russell.
---

diff --git a/Doc/ACKS.txt b/Doc/ACKS.txt
index 32943bddd5..7344cf8dac 100644
--- a/Doc/ACKS.txt
+++ b/Doc/ACKS.txt
@@ -158,6 +158,7 @@ docs@python.org), and we'll be glad to correct the problem.
    * Jim Roskind
    * Guido van Rossum
    * Donald Wallace Rouse II
+   * Mark Russell
    * Nick Russo
    * Chris Ryland
    * Constantina S.
diff --git a/Doc/library/functions.rst b/Doc/library/functions.rst
index 4f86fc71c6..693af64563 100644
--- a/Doc/library/functions.rst
+++ b/Doc/library/functions.rst
@@ -977,12 +977,16 @@ available.  They are listed here in alphabetical order.
 
 .. function:: reversed(seq)
 
-   Return a reverse :term:`iterator`.  *seq* must be an object which supports
-   the sequence protocol (the :meth:`__len__` method and the :meth:`__getitem__`
-   method with integer arguments starting at ``0``).
+   Return a reverse :term:`iterator`.  *seq* must be an object which has
+   a :meth:`__reversed__` method or supports the sequence protocol (the
+   :meth:`__len__` method and the :meth:`__getitem__` method with integer
+   arguments starting at ``0``).
 
    .. versionadded:: 2.4
 
+   .. versionchanged:: 2.6
+      Added the possibility to write a custom :meth:`__reversed__` method.
+
 
 .. function:: round(x[, n])
 
diff --git a/Doc/reference/datamodel.rst b/Doc/reference/datamodel.rst
index 7ea6ca757a..ed05b322c8 100644
--- a/Doc/reference/datamodel.rst
+++ b/Doc/reference/datamodel.rst
@@ -1796,6 +1796,22 @@ sequences, it should iterate through the values.
    Iterator objects also need to implement this method; they are required to return
    themselves.  For more information on iterator objects, see :ref:`typeiter`.
 
+
+.. method:: object.__reversed__(self)
+
+   Called (if present) by the :func:`reversed` builtin to implement
+   reverse iteration.  It should return a new iterator object that iterates
+   over all the objects in the container in reverse order.
+
+   If the :meth:`__reversed__` method is not provided, the
+   :func:`reversed` builtin will fall back to using the sequence protocol
+   (:meth:`__len__` and :meth:`__getitem__`).  Objects should normally
+   only provide :meth:`__reversed__` if they do not support the sequence
+   protocol and an efficient implementation of reverse iteration is possible.
+
+   .. versionadded:: 2.6
+
+
 The membership test operators (:keyword:`in` and :keyword:`not in`) are normally
 implemented as an iteration through a sequence.  However, container objects can
 supply the following special method with a more efficient implementation, which