以下是一个示例代码，演示了如何比较两个对象并导出差异：

import json

def compare_objects(obj1, obj2):
    diff = {}
    
    # 比较obj1中的每个键值对
    for key in obj1:
        if key not in obj2:
            diff[key] = {
                "old_value": obj1[key],
                "new_value": None
            }
        elif obj1[key] != obj2[key]:
            diff[key] = {
                "old_value": obj1[key],
                "new_value": obj2[key]
            }
    
    # 检查obj2中是否有obj1中没有的键值对
    for key in obj2:
        if key not in obj1:
            diff[key] = {
                "old_value": None,
                "new_value": obj2[key]
            }
    
    return diff

# 两个示例对象
obj1 = {
    "name": "John",
    "age": 30,
    "city": "New York"
}

obj2 = {
    "name": "John",
    "age": 35,
    "country": "USA"
}

# 比较并导出差异
diff = compare_objects(obj1, obj2)

# 将差异导出为JSON格式
diff_json = json.dumps(diff, indent=4)
print(diff_json)

运行这段代码将输出如下结果：

{
    "age": {
        "old_value": 30,
        "new_value": 35
    },
    "city": {
        "old_value": "New York",
        "new_value": null
    },
    "country": {
        "old_value": null,
        "new_value": "USA"
    }
}

这个示例代码会比较obj1和obj2两个对象的键值对，找出差异，并将差异导出为JSON格式的字符串。在差异对象中，每个键值对都包含了旧值和新值。如果某个键值对只存在于一个对象中，则将另一个值设为None。