#!/usr/bin/env python 
#定義一個列表來模擬棧 
stack = [] 
#進棧,調用列表的append()函數(shù)加到列表的末尾,strip()沒有參數(shù)是去掉首尾的空格 
def pushit(): 
  stack.append(raw_input('Enter new string: ').strip()) 
#出棧,用到了pop()函數(shù) 
def popit(): 
  if len(stack) == 0: 
    print 'Cannot pop from an empty stack!' 
  else: 
    print 'Removed [', stack.pop(), ']' 
#編歷棧 
def viewstack(): 
  print stack 
#CMDs是字典的使用 
CMDs = {'u': pushit, 'o': popit, 'v': viewstack} 
#pr為提示字符 
def showmenu(): 
  pr = """ 
  p(U)sh 
  p(O)p 
  (V)iew 
  (Q)uit 
    Enter choice: """ 
  while True: 
    while True: 
      try: 
        #先用strip()去掉空格,再把第一個字符轉換成小寫的 
        choice = raw_input(pr).strip()[0].lower() 
      except (EOFError, KeyboardInterrupt, IndexError): 
        choice = 'q' 
      print '\nYou picked: [%s]' % choice 
      if choice not in 'uovq': 
        print 'Invalid option, try again' 
      else: 
        break 
#CMDs[]根據(jù)輸入的choice從字典中對應相應的value,比如說輸入u,從字典中得到value為pushit,執(zhí)行pushit()進棧操作 
    if choice == 'q': 
      break 
    CMDs[choice]() 
#判斷是否是從本文件進入,而不是被調用 
if __name__ == '__main__': 
  showmenu()