Breadth-first search in Python.

bfs.py

from typing import Any


def bfs(haystack: dict, needle: Any) -> Any:
    """
    Breadth-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.
    """
    if needle in haystack:
        return haystack[needle]
    value = None
    for k, v in haystack.items():
        if isinstance(v, dict):
            value = bfs(haystack=v, needle=k)
    return value