自动将密钥添加到Python字典

Question

我想自动将键添加到Python字典（如果还不存在）。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'