from typing import Any, Callable, List, Optional, Union

Iter = Union[list, dict, Any]
IterPath = List[Union[int, str]]


def traverse(
    obj: Iter,
    callback: Callable[[Iter, IterPath], Iter],
    path: Optional[IterPath] = None,
) -> Iter:
    """
    Traverse through nested dict or list.
    """
    path = path or []
    if isinstance(obj, dict):
        return {
            key: traverse(value, callback, path + [key]) for key, value in obj.items()
        }
    elif isinstance(obj, list):
        return [
            traverse(elem, callback, path + [index]) for index, elem in enumerate(obj)
        ]
    return callback(obj, path)