python实现堆栈与队列的方法

class Stack(): 
    def __init__(self,size): 
        self.size=size; 
        self.stack=[]; 
        self.top=-1; 
    def push(self,ele):  #入栈之前检查栈是否已满 
        if self.isfull(): 
            raise exception("out of range"); 
        else: 
            self.stack.append(ele); 
            self.top=self.top+1; 
    def pop(self):             # 出栈之前检查栈是否为空 
        if self.isempty(): 
            raise exception("stack is empty"); 
        else: 
            self.top=self.top-1; 
            return self.stack.pop(); 
     
    def isfull(self): 
        return self.top+1==self.size; 
    def isempty(self): 
        return self.top==-1;

#!/usr/bin/python  
from stack import Stack 
s=Stack(20); 
for i in range(3): 
    s.push(i); 
s.pop() 
print s.isempty();

class Queue(): 
    def __init__(self,size): 
        self.size=size; 
        self.front=-1; 
        self.rear=-1; 
        self.queue=[]; 
    def enqueue(self,ele):  #入队操作 
        if self.isfull(): 
            raise exception("queue is full"); 
        else: 
            self.queue.append(ele); 
            self.rear=self.rear+1; 
    def dequeue(self):      #出队操作 
        if self.isempty(): 
            raise exception("queue is empty"); 
        else: 
            self.front=self.front+1; 
            return self.queue[self.front]; 
    def isfull(self): 
        return self.rear-self.front+1==self.size; 
    def isempty(self): 
        return self.front==self.rear; 
     
q=Queue(10); 
for i in range(3): 
    q.enqueue(i); 
print q.dequeue(); 
print q.isempty();