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Merged revisions 79525 via svnmerge from 

svn+ssh://pythondev@svn.python.org/python/branches/py3k

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  r79525 | ezio.melotti | 2010-03-31 10:45:32 +0300 (Wed, 31 Mar 2010) | 9 lines

  Merged revisions 79522 via svnmerge from
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    r79522 | ezio.melotti | 2010-03-31 10:26:24 +0300 (Wed, 31 Mar 2010) | 1 line

    Revert r79179 and merge r75584 to explain how to implement a queue using collection.deque instead of a list.
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Ezio Melotti 2010-03-31 07:48:01 +00:00
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Doc/tutorial/datastructures.rst
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@ -137,21 +137,25 @@ Using Lists as Queues
.. sectionauthor:: Ka-Ping Yee <ping@lfw.org>
It is also possible to use a list as a queue, where the first element added is
the first element retrieved ("first-in, first-out"); however, lists are not
efficient for this purpose. While appends and pops from the end of list are
fast, doing inserts or pops from the beginning of a list is slow (because all
of the other elements have to be shifted by one).
You can also use a list conveniently as a queue, where the first element added
is the first element retrieved ("first-in, first-out"). To add an item to the
back of the queue, use :meth:`append`. To retrieve an item from the front of
the queue, use :meth:`pop` with ``0`` as the index. For example::
To implement a queue, use :class:`collections.deque` which was designed to
have fast appends and pops from both ends. For example::
>>> queue = ["Eric", "John", "Michael"]
>>> from collections import deque
>>> queue = deque(["Eric", "John", "Michael"])
>>> queue.append("Terry") # Terry arrives
>>> queue.append("Graham") # Graham arrives
>>> queue.pop(0)
>>> queue.popleft() # The first to arrive now leaves
'Eric'
>>> queue.pop(0)
>>> queue.popleft() # The second to arrive now leaves
'John'
>>> queue
['Michael', 'Terry', 'Graham']
>>> queue # Remaining queue in order of arrival
deque(['Michael', 'Terry', 'Graham'])
.. _tut-listcomps: