字典的嵌套:
>>> from collections import defaultdict
>>> a = defaultdict(dict)
>>> a['hell']['good']= 1
>>> a
defaultdict(<class 'dict'>, {'hell': {'good': 1}})
字典的嵌套:
>>> from collections import defaultdict
>>> a = defaultdict(dict)
>>> a['hell']['good']= 1
>>> a
defaultdict(<class 'dict'>, {'hell': {'good': 1}})