腾讯云 凭据无法工作

import os
from tencentcloud.common import credential
from tencentcloud.common.profile.client_profile import ClientProfile
from tencentcloud.common.profile.http_profile import HttpProfile
from tencentcloud.common.exception.tencent_cloud_sdk_exception import TencentCloudSDKException
from tencentcloud.cvm.v20170312 import cvm_client, models

try:
    # 设置凭据
    cred = credential.Credential("你的SecretId", "你的SecretKey")
    
    httpProfile = HttpProfile()
    httpProfile.endpoint = "cvm.tencentcloudapi.com"

    clientProfile = ClientProfile()
    clientProfile.httpProfile = httpProfile
    client = cvm_client.CvmClient(cred, "ap-guangzhou", clientProfile)

    # 发起请求
    req = models.DescribeInstancesRequest()
    params = '{"Limit": 1}'
    req.from_json_string(params)

    resp = client.DescribeInstances(req)
    print(resp.to_json_string())

except TencentCloudSDKException as err:
    print(err)