给定一个json字符串，将嵌套的json字符串转换为键值对，其中键是元素层次结构的名称，并附加“_”

import json

def flatten_json(json_obj, prefix=''):
    flattened_dict = {}
    
    if isinstance(json_obj, dict):
        for key in json_obj:
            new_key = prefix + key + '_'
            if isinstance(json_obj[key], (dict, list)):
                flattened_dict.update(flatten_json(json_obj[key], new_key))
            else:
                flattened_dict[new_key[:-1]] = json_obj[key]
    
    elif isinstance(json_obj, list):
        for i in range(len(json_obj)):
            new_key = prefix + str(i) + '_'
            if isinstance(json_obj[i], (dict, list)):
                flattened_dict.update(flatten_json(json_obj[i], new_key))
            else:
                flattened_dict[new_key[:-1]] = json_obj[i]
    
    return flattened_dict

# 示例json字符串
json_str = '{"name": "John", "age": 30, "address": {"street": "123 Main St", "city": "New York"}}'

# 解析json字符串
json_obj = json.loads(json_str)

# 转换为键值对
result = flatten_json(json_obj)

# 打印结果
for key, value in result.items():
    print(key + ':', value)

name: John
age: 30
address_street: 123 Main St
address_city: New York