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| -rw-r--r-- | Doc/tutorial/datastructures.rst | 27 |
1 files changed, 13 insertions, 14 deletions
diff --git a/Doc/tutorial/datastructures.rst b/Doc/tutorial/datastructures.rst index 8cf58c8..b562558 100644 --- a/Doc/tutorial/datastructures.rst +++ b/Doc/tutorial/datastructures.rst @@ -137,26 +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'] - -However, since lists are implemented as an array of elements, they are not the -optimal data structure to use as a queue (the ``pop(0)`` needs to move all -following elements). See :ref:`tut-list-tools` for a look at -:class:`collections.deque`, which is designed to work efficiently as a queue. + >>> queue # Remaining queue in order of arrival + deque(['Michael', 'Terry', 'Graham']) .. _tut-listcomps: |