当层次结构中的键位置事先不知道时，如何访问嵌套的Python字典键值对？

# 示例字典
data = {
    "key1": {
        "nested_key1": "value1",
        "nested_key2": "value2"
    },
    "key2": {
        "nested_key3": "value3",
        "nested_key4": "value4"
    }
}

# 访问嵌套的键值对
value1 = data["key1"]["nested_key1"]
value2 = data["key1"]["nested_key2"]
value3 = data["key2"]["nested_key3"]
value4 = data["key2"]["nested_key4"]

# 打印结果
print(value1)  # 输出: value1
print(value2)  # 输出: value2
print(value3)  # 输出: value3
print(value4)  # 输出: value4

data = {
    "key1": {
        "nested_key1": "value1"
    }
}

try:
    value = data["unknown_key"]["nested_key1"]
except KeyError:
    print("无法找到指定的键值对")