用python计数字典里其中一个键嵌套的键出现次数

假设有如下字典：

my_dict = {
    "key1": {
        "nested_key1": "value1",
        "nested_key2": "value2"
    },
    "key2": {
        "nested_key1": "value3",
        "nested_key2": "value4"
    },
    "key3": {
        "nested_key1": "value5",
        "nested_key2": "value6",
        "nested_key3": {
            "nested_nested_key1": "value7"
        }
    }
}

现在要计算嵌套在`"nested_key1"`键下面的值出现的次数。可以使用以下代码：

count_dict = {}

for key, value in my_dict.items():
    if "nested_key1" in value:
        nested_value = value["nested_key1"]
        if nested_value in count_dict:
            count_dict[nested_value] += 1
        else:
            count_dict[nested_value] = 1

print(count_dict)

输出结果为：

{'value1': 1, 'value3': 1, 'value5': 1}

其中，`count_dict`记录了嵌套在`"nested_key1"`键下面的值出现的次数。