如何更新比较两个字典的关键字？

def update_dict(source_dict, target_dict):
    for key, value in source_dict.items():
        if key in target_dict:
            if target_dict[key] != value:
                target_dict[key] = value
        else:
            target_dict[key] = value

# 示例用法
source_dict = {"key1": "value1", "key2": "value2", "key3": "value3"}
target_dict = {"key1": "old_value", "key4": "old_value"}

update_dict(source_dict, target_dict)
print(target_dict)