基于字典中的键的嵌套defaultdict

Question

I'm trying to create a defaultdict within a defaultdict based on a key value. My thinking may be completely wrong here, but here's the code for a basic defaultdict;

def record():
    return {
        'count': 0,
        'key1': Counter(),      
    }

1_record = defaultdict(record)

But what if I want to add a key as a defaultdict like this;

def record():
    return {
        'count': 0,
        'key1': Counter(),
        'key2': {
            'count': 0,
            'nested_key1': Counter()

    }
}

In the above how could I make 'key2' a defaultdict? Is this even possible or am I approaching the problem the wrong way?

Answer 1

You definitely can have a "recursive" defaultdict:

>>> from collections import defaultdict
>>> def record():
...   return {
...     'key': defaultdict(record)
...   }
... 
>>> d = defaultdict(record)
>>> 
>>> d['foo']
{'key': defaultdict(<function record at 0x10b396f50>, {})}
>>> d['foo']['key']['bar']
{'key': defaultdict(<function record at 0x10b396f50>, {})}
>>> d
defaultdict(<function record at 0x10b396f50>, {'foo': {'key': defaultdict(<function record at 0x10b396f50>, {'bar': {'key': defaultdict(<function record at 0x10b396f50>, {})}})}})

However, swapping out the names of the keys at different levels would probably require some special-casing and would make the code a bit more messy...