python - How to use dict.get() with multidimensional dict?

Question

I have a multidimensional dict, and I'd like to be able to retrieve a value by a key:key pair, and return 'NA' if the first key doesn't exist. All of the sub-dicts have the same keys.

d = {   'a': {'j':1,'k':2},
        'b': {'j':2,'k':3},
        'd': {'j':1,'k':3}
    }

I know I can use d.get('c','NA') to get the sub-dict if it exists and return 'NA' otherwise, but I really only need one value from the sub-dict. I'd like to do something like d.get('c['j']','NA') if that existed.

Right now I'm just checking to see if the top-level key exists and then assigning the sub-value to a variable if it exists or 'NA' if not. However, I'm doing this about 500k times and also retrieving/generating other information about each top-level key from elsewhere, and I'm trying to speed this up a little bit.

Answer 1

How about

d.get('a', {'j': 'NA'})['j']

?

If not all subdicts have a j key, then

d.get('a', {}).get('j', 'NA')

 

To cut down on identical objects created, you can devise something like

class DefaultNASubdict(dict):
    class NADict(object):
        def __getitem__(self, k):
            return 'NA'

    NA = NADict()

    def __missing__(self, k):
        return self.NA

nadict = DefaultNASubdict({
                'a': {'j':1,'k':2},
                'b': {'j':2,'k':3},
                'd': {'j':1,'k':3}
            })

print nadict['a']['j']  # 1
print nadict['b']['j']  # 2
print nadict['c']['j']  # NA

 

Same idea using defaultdict:

import collections

class NADict(object):
    def __getitem__(self, k):
        return 'NA'

    @staticmethod
    def instance():
        return NADict._instance

NADict._instance = NADict()


nadict = collections.defaultdict(NADict.instance, {
                'a': {'j':1,'k':2},
                'b': {'j':2,'k':3},
                'd': {'j':1,'k':3}
            })