iteritems：以迭代器对象返回字典键值对
item:以列表形式返回字典键值对
>>> dic = {'a':3,'c':1,'b':2} >>> print dic.iteritems() <dictionary-itemiterator object at 0x7fa381599628> >>> print dic.items() [('a', 3), ('c', 1), ('b', 2)]
两个返回的结果都可迭代
