Python实现堆栈

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()