#!/usr/bin/python
#Copyleft (C) 1996 William Totten
#biell@udel.edu

#This program implements a stack data structure and its methods

class stack:
	def __init__(*a):
		if(len(a)==1):
			a[0].data=[]
		else:
			a[0].data=a[1][:]
	def set(s,l):
		s.data=l
	def __str__(s):
		return str(s.data)
	def push(s, elt):
		s.data.append(elt)
	def pop(s):
		tmp=s.data[-1]
		del s.data[-1]
		return tmp
	def isempty(s):
		return s.data==[]
	def peek(s):
		return s.data[-1]