ArrayStack.py

# -*- coding: utf-8 -*-
"""
Spyder Editor

This temporary script file is located here:
/home/akshay/.spyder2/.temp.py
"""
class Empty(Exception):
    '''Error attempting to access an element from an empty container.'''
    pass
class ArrayStack:
    '''LIFO Stack implementation using a Python list as underlying storage.'''
    
    def __init__(self):
        self.data = []
        
    def __len__(self):
        return len(self.data)
        
    def is_empty(self):
        return (len(self.data == 0))
    
    def push(self, e):
        return self.data.append(e)
    
    def top(self):
        if self.is_empty():
            return Empty('Stack is empty')
        return self.data[-1]
    
    def pop(self):
        if self.is_empty():
            return Empty('Stack is empty')
        return self.data.pop()