python - 自动将键添加到 Python dict

Question

如果它们不存在，我想自动将键添加到 Python 字典中。例如，

a = "a"
b = "b"
c = "c"

dict = {}
dict[a][b] = c # doesn't work because dict[a] doesn't exist

如果密钥不存在，如何自动创建密钥？

Answer 1

使用collections.defaultdict：

def recursively_default_dict():
    return collections.defaultdict(recursively_default_dict)

my_dict = recursively_default_dict()
my_dict['a']['b'] = 'c'

Answer 2

from collections import defaultdict
d = defaultdict(dict)
d['a']['b'] = 'c'

另外，使用时请小心dict-它在python中具有含义：https ://docs.python.org/2/library/stdtypes.html#dict

Answer 3

对于简短的脚本，您还可以使用这一行：

d = {}
d.setdefault(a, {})[b] = c