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#1582: document __reversed__, patch by Mark Russell.

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Georg Brandl 2008-01-06 16:17:56 +00:00
parent ec32b6bce7
commit 81de0d24d5
3 changed files with 24 additions and 3 deletions
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1
Doc/ACKS.txt
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@ -158,6 +158,7 @@ docs@python.org), and we'll be glad to correct the problem.
* Jim Roskind * Jim Roskind
* Guido van Rossum * Guido van Rossum
* Donald Wallace Rouse II * Donald Wallace Rouse II
* Mark Russell
* Nick Russo * Nick Russo
* Chris Ryland * Chris Ryland
* Constantina S. * Constantina S.

10
Doc/library/functions.rst
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@ -977,12 +977,16 @@ available. They are listed here in alphabetical order.
.. function:: reversed(seq) .. function:: reversed(seq)
Return a reverse :term:`iterator`. *seq* must be an object which supports Return a reverse :term:`iterator`. *seq* must be an object which has
the sequence protocol (the :meth:`__len__` method and the :meth:`__getitem__` a :meth:`__reversed__` method or supports the sequence protocol (the
method with integer arguments starting at ``0``). :meth:`__len__` method and the :meth:`__getitem__` method with integer
arguments starting at ``0``).
.. versionadded:: 2.4 .. versionadded:: 2.4
.. versionchanged:: 2.6
Added the possibility to write a custom :meth:`__reversed__` method.
.. function:: round(x[, n]) .. function:: round(x[, n])

16
Doc/reference/datamodel.rst
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@ -1796,6 +1796,22 @@ sequences, it should iterate through the values.
Iterator objects also need to implement this method; they are required to return Iterator objects also need to implement this method; they are required to return
themselves. For more information on iterator objects, see :ref:`typeiter`. 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 The membership test operators (:keyword:`in` and :keyword:`not in`) are normally
implemented as an iteration through a sequence. However, container objects can implemented as an iteration through a sequence. However, container objects can
supply the following special method with a more efficient implementation, which supply the following special method with a more efficient implementation, which