#1582: document __reversed__, patch by Mark Russell.

1 files changed, 16 insertions, 0 deletions

diff --git a/Doc/reference/datamodel.rst b/Doc/reference/datamodel.rst
index 7ea6ca7..ed05b32 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