如何获取多维数组中最长的单词？

def find_longest_word(arr):
    longest_word = ''
    for item in arr:
        if isinstance(item, list):
            word = find_longest_word(item)
            if len(word) > len(longest_word):
                longest_word = word
        elif isinstance(item, str):
            if len(item) > len(longest_word):
                longest_word = item
    return longest_word