12. trick

构造嵌套字典

>>> from collections import defaultdict
>>> tree = lambda : defaultdict(tree)
>>> t = tree()
>>> t['a']['b'] = 1
>>> t['c'] = 1
>>> t['d']['e']['f'] = 10
>>> t
defaultdict(<function __main__.<lambda>()>,
            {'a': defaultdict(<function __main__.<lambda>()>, {'b': 1}),
             'c': 1,
             'd': defaultdict(<function __main__.<lambda>()>,
                         {'e': defaultdict(<function __main__.<lambda>()>,
                                      {'f': 10})})})