helper methods to access/modify nested dictionary structure in python

nested_dict.py

from typing import (
    Any,
    Dict,
    Optional,
    Union,
    Tuple,
    Hashable,
    List
)

RAISE_IF_MISSING = object()

DictKeys = Union[List[Hashable], Tuple[Hashable, ...]]


def get_value_at(
        d: Dict,
        path: DictKeys,
        default: Optional[Any] = None
) -> Any:
    value = d

    for p in path:
        try:
            value = value[p]
        except KeyError:
            if default is RAISE_IF_MISSING:
                raise
            return default

    return value


def set_value_at(
        d: Dict,
        path: DictKeys,
        value: Any
) -> Dict:
    # does NOT copy the dict
    # modifies it and returns it

    if not path:
        raise ValueError('path must not be empty')

    subdict = d

    for p in path[:-1]:
        assert isinstance(subdict, dict)

        if p not in subdict:
            subdict[p] = {}

        subdict = subdict[p]

    subdict[path[-1]] = value

    return d