嵌套的JSON提取第一级键并添加到列Python 3？

import json

def extract_keys(json_data):
    keys = []
    if isinstance(json_data, dict):
        for key in json_data.keys():
            keys.append(key)
            keys.extend(extract_keys(json_data[key]))
    elif isinstance(json_data, list):
        for item in json_data:
            keys.extend(extract_keys(item))
    return keys

# 示例JSON数据
json_str = '''
{
  "key1": "value1",
  "key2": {
    "nested_key1": "nested_value1",
    "nested_key2": "nested_value2"
  },
  "key3": [
    {
      "nested_key3": "nested_value3"
    },
    {
      "nested_key4": "nested_value4"
    }
  ]
}
'''

# 解析JSON数据
data = json.loads(json_str)

# 提取第一级键
keys = extract_keys(data)

# 打印结果
print(keys)

['key1', 'key2', 'key3']