问如何调用查询实例列表api？

# 解决腾讯自签名证书问题 message:[SSL: CERTIFICATE_VERIFY_FAILED]

import ssl

ssl._create_default_https_context=ssl._create_unverified_context

import json

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:

# 实例化一个认证对象，入参需要传入腾讯云账户secretId，secretKey,此处还需注意密钥对的保密

# 密钥可前往https://console.cloud.tencent.com/cam/capi网站进行获取

    cred = credential.Credential("AKID4vH3qlk865KK", "1ElYPvDnIEsI7wiWM")

# 实例化一个http选项，可选的，没有特殊需求可以跳过

    httpProfile = HttpProfile()

    httpProfile.endpoint = "cvm.tencentcloudapi.com"

# 实例化一个client选项，可选的，没有特殊需求可以跳过

    clientProfile = ClientProfile()

    clientProfile.httpProfile = httpProfile

# 实例化要请求产品的client对象,clientProfile是可选的

    client = cvm_client.CvmClient(cred, "", clientProfile)

# 实例化一个请求对象,每个接口都会对应一个request对象

    req = models.DescribeInstancesRequest()

    params = {

    }

    req.from_json_string(json.dumps(params))

# 返回的resp是一个DescribeInstancesResponse的实例，与请求对象对应

    resp = client.DescribeInstances(req)

# 输出json格式的字符串回包

print(resp.to_json_string())

except TencentCloudSDKException as err:

print(err)

代码如上 返回报错

[TencentCloudSDKException] code:ClientNetworkError message:HTTPSConnectionPool(host='cvm.tencentcloudapi.com', port=443): Max retries exceeded with url: / (Caused by ProxyError('Cannot connect to proxy.', timeout('_ssl.c:1029: The handshake operation timed out'))) requestId:None