I’m trying to create a nested dictionary in python so that, given a list of strings, the dictionary records the number of occurrences of that string order.

For example: if the string list is ["hey", "my", "name", "is"], I would want the nested dictionary to look like:

{"hey": {"my": {"name": {"is": 1}}}}

I know I could probably use as key the whole list but I specifically want to separate the strings in the dictionary.

I also would want to approach this problem with a defaultdict dictionary, and not the Python ones, and preferably, use a recursively defined defaultdict.

This is what I tried:

from collections import defaultdict

nested_dict = lambda: defaultdict(nested_dict)
# Initialize ngrams as a nested defaultdict
ngrams = nested_dict()

# Function to update the nested defaultdict with the list of words
def update_ngrams(ngrams, words):
   current_dict = ngrams
   for word in words[:-1]:
       current_dict = current_dict[word]
   current_dict[words[-1]] += 1

# Example usage
update_ngrams(ngrams, ["My", "big", "cat"])
update_ngrams(ngrams, ["My", "big", "dog"])

But it gives me this error:

TypeError: unsupported operand type(s) for +=: 'collections.defaultdict' and 'int'

The expected output should be a map like this:

{"My": {"big": {"cat": 1, "dog": 1}}}

Thanks!