如何遍历python字典并替换子字符串值？

def replace_substring(dictionary, old_substring, new_substring):
    for key, value in dictionary.items():
        if isinstance(value, str):
            dictionary[key] = value.replace(old_substring, new_substring)
        elif isinstance(value, dict):
            replace_substring(value, old_substring, new_substring)

# 示例字典
my_dict = {
    "name": "John",
    "age": 30,
    "address": {
        "street": "123 Main St",
        "city": "New York",
        "country": "USA"
    }
}

# 替换子字符串
replace_substring(my_dict, "New", "Old")

# 输出替换后的字典
print(my_dict)