如何向嵌套序列化程序添加默认值？

def add_default_value(data):
    if isinstance(data, dict):
        for key, value in data.items():
            if isinstance(value, dict) or isinstance(value, list):
                add_default_value(value)  # 递归处理嵌套的字典或列表
            elif value is None:
                data[key] = "default"  # 添加默认值
    elif isinstance(data, list):
        for item in data:
            if isinstance(item, dict) or isinstance(item, list):
                add_default_value(item)  # 递归处理嵌套的字典或列表
            elif item is None:
                item = "default"  # 添加默认值

# 示例数据
data = {
    "name": "John",
    "age": None,
    "address": {
        "street": "123 Main St",
        "city": None,
        "country": "USA"
    },
    "hobbies": ["reading", None, "swimming"]
}

add_default_value(data)
print(data)