Implementation of building nested dictionary from list

Question

I have a value test-1 and a list of keys as below:

[
  ["initial", "short_title"],
  ["later", "datasets", "item_okmiwt"],
  ["general_title"]
]

I wanted the resulting dictionary like this:

{'initial': {'short_title': 'test-1'}, 'later': {'datasets': {'item_okmiwt': 'test-1'}}, 'general_title': 'test-1'}

I have written the following code for implementing the above result:

def set_copy_to_attr(value, copy_to_attr):
    """Method to copy value to copy_to config."""

    def build_nested_dict(element, result={}):
        if len(element) == 1:
            result[element[-1]] = pid_value
            return result
        else:
            for el in element:
                result[el] = {}
                element.remove(el)
                build_nested_dict(element, result[el])

    for _element in copy_to_attr:
        _dict = build_nested_dict(_element)

    if _dict:
        return _dict

I am getting the desired result, Is this approach can be optimized more?

Answer 1

Broadly: this kind of dictionary soup is a problem, and is often evidence of inadequate domain modelling and deserialisation. But you haven't shown enough of your actual application to say more.

Two things will slow you down: mutating element via .remove(), and recursing. Python is bad at recursing, and for input of sufficient depth this will easily blow the stack.

Add PEP484 type hints - even though, since this is dictionary soup, typing is made more difficult.

Rather than _dict (making it look like a private), typically to avoid Python keywords, the underscore is a suffix i.e. dict_.

Suggested

from pprint import pprint
from typing import Any, Iterable


def set_copy_to_attr(
    value: Any,
    copy_to_attr: Iterable[Iterable[Any]],
) -> dict:
    dict_ = {}

    for *values, leaf in copy_to_attr:
        nested = dict_
        for v in values:
            nested[v] = nested = {}
        nested[leaf] = value

    return dict_


def test() -> None:
    copy_to_attr = [
      ["initial", "short_title"],
      ["later", "datasets", "item_okmiwt"],
      ["general_title"]
    ]

    copied = set_copy_to_attr('test-1', copy_to_attr)
    pprint(copied)


if __name__ == '__main__':
    test()

Output

{'general_title': 'test-1',
 'initial': {'short_title': 'test-1'},
 'later': {'datasets': {'item_okmiwt': 'test-1'}}}