步骤一：对字典进行items方法：
>>>addict = {'a':3,'b':1,'c':2}
>>>addict.items()
>>> [('a',3),('b',1),('c',2)]
步骤二：字典的operator方法:
>>>import operator
>>>aim_adict = sorted(addict.items(),key = operator.itemgetter(1),reverse = True)
>>>aim_adict = [('a',3),('c',2),('b',1)]
