在Python中指定keytab文件进行Kerberos认证，你需要用到gssapi库。首先，确保已经安装了相应的库：

pip install gssapi requests-kerberos  

然后，可以使用以下代码来进行认证：

import requests  
from requests_kerberos import HTTPKerberosAuth, REQUIRED  
import os  
from gssapi.raw import acquire_cred_with_password  
from getpass import getpass  
os.environ["KRB5_CLIENT_KTNAME"] = "/path/to/your/keytab"  
# your service name, like 'HTTP/host@YOUR-REALM.COM'  
service_name = "<service-name>"  
password = getpass("Enter password for {0}: ".format(service_name))  
name = gssapi.Name(service_name, gssapi.NameType.kerberos_principal)  
cred = acquire_cred_with_password(name, password)  
auth = HTTPKerberosAuth(mutual_authentication=REQUIRED, force_preemptive=True,  
                        delegate=True, principal=cred.name, hostname_override="server-name")  
url = "http://your_kylin_instance:7070/kylin/api/cubes"  
response = requests.get(url, auth=auth)  
print(response.json())  

请注意替换"/path/to/your/keytab"为你的keytab文件的实际路径，<service-name>为你的服务名，以及替换http://your_kylin_instance:7070/kylin/api/cubes为Kylin实例的URL。

这会创建一个基于你的keytab和密码的GSSAPI凭据，并用其去请求Kerberos认证。