Python uses a single-linked list to implement queues (class-based, including iterators)

#!/usr/bin/python #-*-Coding:utf-8-*-"Created on 2015-2-3@author:beyondzhou@name:test_linklistqueue.py" def Test_linklistqueue (): # import Pylistqueue from myqueue import linklistqueue print ' #Init a queue named S Mith using Enqueue ' Smith = Linklistqueue () smith.enqueue (' CSCI-112 ') smith.enqueue (' MATH-121 ') smith.enqueue ( ' HIST-340 ') smith.enqueue (' ECON-101 ') print ' \n#output Smith queue ' for element in Smith:print Elemen T print ' \n#dequeue one item ' Smith.dequeue () print ' \n#output Smith after dequeue ' for element i n smith:print element Smith.enqueue (' ECON-102 ') print ' \n#output Smith after enqueue again ' fo R element in Smith:print element print ' \n#get the length of the queue ' print ' The lenght of the queue is '    , Len (Smith) print ' \n#check wheter the queue is empty ' if Smith.isempty (): print ' queue is empty! ' Else:print ' queue is noT empty! ' print ' \n#dequeue all items ' and not Smith.isempty (): Smith.dequeue () print ' \n#check wheter the queue    is empty after dequeue all items ' if Smith.isempty (): print ' queue is empty! '            Else:print ' queue is not empty! ' print ' \n#init again ' smith.enqueue (' CSCI-112 ') smith.enqueue (' MATH-121 ') smith.enqueue (' HIST-340 ') smith.enqu Eue (' ECON-101 ') print ' \n#output Smith queue ' for element in Smith:print element if __name__ = = "__ma In__ ": Test_linklistqueue ()

# Implementation of the Queue ADT using a linked ListClass Linklistqueue: # Creates an empty Queue def __init__ (self ): Self._qhead = None Self._qtail = None Self._count = 0 # Returns True if the queue is empty D        EF IsEmpty (self): return self._qhead was None # Returns the number of items in the queue def __len__ (self): Return Self._count # Adds The given item to the queue Def enqueue (self, item): node = _linklistqueuenode (item) if Self.isempty (): self._qhead = node Else:self._qtail.next = node Self . _qtail = node Self._count + = 1 # removes and returns the first item in the Queue Def dequeue (self): a        Ssert not Self.isempty (), "cannot dequeue from an empty queue." node = Self._qhead if Self._qhead is self._qtail:self._qtail = None Self._qhead = self._qhead.ne XT Self._count-= 1 return Node.item # Returns an iterator For traversing the list of items Def __iter__ (self): return _linklistqueueiterator (self._qhead) # Private Storag E class for creating the linked list Nodesclass _linklistqueuenode (object): Def __init__ (self, item): Self.item = Item Self.next = none# defines a linked list iterator class _linklistqueueiterator:def __init__ (self, queuehe  AD): Self._curnode = Queuehead def __iter__ (self): return self def next (self): if Self._curnode is none:raise stopiteration Else:item = Self._curnode.item Self._curnode = self . _curnode.next Return Item

#Init a queue named Smith using Enqueue#output Smith queuecsci-112math-121hist-340econ-101#dequeue one item#output Smith a Fter Dequeuemath-121hist-340econ-101#output Smith after enqueue againmath-121hist-340econ-101econ-102#get the length  of queuethe lenght of the queue is  4#check wheter the queue is Emptyqueue are not empty! #dequeue all Items#check wheter the Queue is empty after dequeue all itemsqueue are empty! #init again#output Smith queuecsci-112math-121hist-340econ-101

Python uses a single-linked list to implement queues (class-based, including iterators)