#!/usr/bin/env python queue = [] def enQ():   queue.append(raw_input('Enter new string: ').strip())#調用list的列表的pop()函數.pop(0)為列表的第一個元素 def deQ():   if len(queue) == 0:     print 'Cannot pop from an empty queue!'   else:     print 'Removed [', queue.pop(0) ,']' def viewQ():   print queue CMDs = {'e': enQ, 'd': deQ, 'v': viewQ} def showmenu():   pr = """   (E)nqueue   (D)equeue   (V)iew   (Q)uit     Enter choice: """   while True:     while True:       try:         choice = raw_input(pr).strip()[0].lower()       except (EOFError, KeyboardInterrupt, IndexError):        choice = 'q'       print '/nYou picked: [%s]' % choice       if choice not in 'devq':         print 'Invalid option, try again'       else:         break     if choice == 'q':       break     CMDs[choice]() if __name__ == '__main__':   showmenu()