python修改嵌套列表中的字符串

def modify_nested_list(lst, old_str, new_str):
    for i in range(len(lst)):
        if isinstance(lst[i], list):
            modify_nested_list(lst[i], old_str, new_str)
        elif isinstance(lst[i], str):
            lst[i] = lst[i].replace(old_str, new_str)

nested_list = [['apple', 'banana'], ['orange', 'grape'], 'pineapple']
modify_nested_list(nested_list, 'apple', 'fruit')
print(nested_list)

[['fruit', 'banana'], ['orange', 'grape'], 'pinefruit']