Queue python

# -*-coding: utf-8 -*-
# Author :writen by Qiusheng Li
# Time: 2014/08/16
# Email:[email protected]
# enqueue Insert an item at the back of the queue
# dequeue Remove an item from the front of the queue
# peek/front Retrieve an item at front of the queue without removing it
# empty/size Check whether the queue is empty or return its size
# using list impliment the Queue

class Queue(object):
    '''a class of Queue'''
    def __init__(self):
        self.items = []
        
    def isEmpty(self):
        return self.items == []
    
    def enqueue(self, value):
        self.items.insert(0,value)# insert value before index(0)
        
    def peek(self):
        if not self.isEmpty():
            return self.items[-1]
        else:
            raise Exception("Queue is empty")
        
    def dequeue(self):
        return self.items.pop() # remove and return item at index(default last).
                                # Raises IndexError if list is empty or index is out of range
                                # without writing if code
    def size(self):
        return len(self.items)

def QueueMain():
    queue = Queue()
    queue.enqueue(1)
    queue.enqueue(2)
    queue.enqueue(3)
    print 'size or empty: ',queue.size()
    print 'peek: ',queue.peek()
    print 'dequeue: ',queue.dequeue()
    print 'size or empty: ',queue.size()
''' testinng result
size or empty:  3
peek:  1
dequeue:  1
size or empty:  2
'''
    
if __name__ == '__main__':
    QueueMain()