How to count the number of occurrences of a nested dictionary key?

Question

I have a nested dictionary:

d = {'key': 1, 'lock':{'key': 3, 'lock': {'key': 7, 'lock': None}}}

and I am hoping to simply get the number of times 'key' occurs. So in this example, the output would be:

3

because 'key' appears 3 times. I know this is pretty straight forward but I'm a bit foggy on how to do this with dictionaries. I would prefer to not use any libraries if possible.

Thanks for the help!

Answer 1

You can use a function that recursively counts the given key:

def count(d, k):
    c = int(k in d)
    for v in d.values():
        if isinstance(v, dict):
            c += count(v, k)
    return c

or to write the above in a more concise way:

def count(d, k):
    return (k in d) + sum(count(v, k) for v in d.values() if isinstance(v, dict))

so that count(d, 'key') returns: 3