python之将字典列表转换为字典集列表

我有一本字典

graph = {'1': ['2', '21'], 
         '2': ['3', '1'], 
         '3': ['4', '2'], 
         '4': ['5', '3'], 
         '5': ['6', '4'], 
         '6': ['12', '5'], 
         '7': ['13', '8'], 
         '8': ['7', '9'], 
         '9': ['8', '10'], 
         '10': ['9', '11']} 

我想输出为

graph = {'1': set(['2', '21']), 
         '2': set(['3', '1']), 
         '3': set(['4', '2']), 
         '4': set(['5', '3']), 
         '5': set(['6', '4']), 
         '6': set(['12', '5']), 
         '7': set(['13', '8']), 
         '8': set(['7', '9']), 
         '9': set(['8', '10']), 
         '10': set(['9', '11'])} 

我是 python 的新手，想不出办法。我试过 zip 但它抛出不可散列类型列表的错误。