How can I recursively modify the keys and values of a nested dictionary?

Question

So I have a nested dictionary of arbitrary depth that is similar to this:

sample_dict = {
    'root_node': {
        'child_1': {
            'child_1a': {
                'child_1a_a': {},
                'child_1a_b': {},
                ...,
                'child_1a_x': {}
            },
            'child_1b': {
                'child_1b_a': {
                    'child_1b_a_a': {},
                    'child_1b_a_b': {},
                    ...
                },
                'child_1b_b': {
                    'child_1b_b_a': {},
                    ...
                },
                'child_1b_c': {}
            }
        },
        'child_2': {
                ...
            }
        }
    }

I need to convert the above dictionary into something like this:

sample_dict_output = {
    'title':'root_node',
    'key':'root_node',
    'children':[
        { 'title':'child_1',
          'key':'child_1',
          'children':[
              {'title':'child_1a',
               'key':'child_1a',
               'children':[
                 {'title': 'child_1a_a',
                  'key': 'child_1a_a'},
                 {'title': 'child_1a_b',
                  'key': 'child_1a_b'},
                   ...
                 {'title': 'child_1a_x',
                  'key': 'child_1a_x'},
               ],},
              {'title':'child_1b',
               'key':'child_1b',
               'children':[
                 {'title': 'child_1b_a',
                  'key': 'child_1b_a',
                  'children':[
                      {'title': 'child_1b_a_a',
                       'key': 'child_1b_a_a'},
                      {'title': 'child_1b_a_b',
                       'key': 'child_1b_a_b'},
                      ...
                  ],},
                 {'title': 'child_1b_b',
                  'key': 'child_1b_b',
                   'children':[
                    {'title': 'child_1b_b_a',
                     'key': 'child_1b_b_a'},
                    ...,
                 ],},
                {'title': 'child_1b_c',
                 'key': 'child_1b_c'}
                ],
              },
        { 'title':'child_2',
          'key':'child_2',
          'children':[...]
        }
    ],
}

I tried to search Stackoverflow for a solution and also attempted recursion, but to no avail. Hence, any help would be appreciated (preferably in Python 3.x). Thank you!

You should navigate into the dictionary, but that's not necessarily recursive. — Bora, Jan 04 '21 at 13:29
Could you even begin to describe in English what the relationship between the output and the input is? *"... convert into something like this."* Really? — Booboo, Jan 04 '21 at 13:30
What if the outer most dict is not a singleton? Shouldn't the whole ouptut be a list? — user2390182, Jan 04 '21 at 13:50

user2390182 · Accepted Answer · 2021-01-04T14:08:36.330

The following will get you in the right direction:

def convert_item(key, val):
    conv = {
        "title": key, 
        "key": key, 
    }
    if val:
        conv["children"] = convert_dict(val)
    return conv

def convert_dict(dct):
    return [
        convert_item(k, v) for k, v in dct.items()
    ]

>>> convert_dict(sample_dict)[0]
{
    "title": "root_node",
    "key": "root_node",
    "children": [
        {
            "title": "child_1",
            "key": "child_1",
            "children": [
                {
                    "title": "child_1a",
                    "key": "child_1a",
                    "children": [
                        {"title": "child_1a_a", "key": "child_1a_a"},
                        {"title": "child_1a_b", "key": "child_1a_b"},
                        {"title": "child_1a_x", "key": "child_1a_x"},
                    ],
                },
                {
                    "title": "child_1b",
                    "key": "child_1b",
                    "children": [
                        {
                            "title": "child_1b_a",
                            "key": "child_1b_a",
                            "children": [
                                {"title": "child_1b_a_a", "key": "child_1b_a_a"},
                                {"title": "child_1b_a_b", "key": "child_1b_a_b"},
                            ],
                        },
                        {
                            "title": "child_1b_b",
                            "key": "child_1b_b",
                            "children": [
                                {"title": "child_1b_b_a", "key": "child_1b_b_a"}
                            ],
                        },
                        {"title": "child_1b_c", "key": "child_1b_c"},
                    ],
                },
            ],
        }
    ],
}

Or with a single recursive function:

def convert_dict(dct):
    return [
        {"title": k, "key": k, **({"children": convert_dict(v)} if v else {})}
        for k, v in dct.items()
    ]

Nope, not really. This is just for convenience and readability, you could easily transform this to a single function. — user2390182, Jan 04 '21 at 14:05
The only issues that can arise are if your data deviates from the given structure or contains a circle (any dict in there containing itself as a (nested) value). But that would make any naive implementation recurse infinitely. — user2390182, Jan 04 '21 at 14:11
`**` unpacks the dictionary it is applied to. This is a trick to flatten in the potentially empty dict containing the "children" key. — user2390182, Jan 04 '21 at 14:41
This does exactly the same as the two-function variant. Inserts the children key only if there are children (a non-empty val). — user2390182, Jan 04 '21 at 14:42

How can I recursively modify the keys and values of a nested dictionary?

1 Answers1