Depth-first search in Python.

dfs.py

from typing import Any


def dfs(haystack: dict, needle: Any) -> Any:
    """
    Depth-first search in a dict for the specified key, for which the
    value is returned.
    :param haystack: The dictionary we want to search.
    :param needle: the key, whose value we are searching for
    :return: the value at the given key or None if not found.
    """
    value = None
    for k, v in haystack.items():
        if isinstance(v, dict):
            return dfs(haystack=v, needle=k)
        if needle in haystack:
            value = haystack[needle]
    return value