Use plpython in PostgreSQL13 function to connect pymssql error

Question

I want to use plpython in postgresql's function. I installed Python3.9 and configured the path and some other configations, and I copied the python's dll into the pg directory (my server is windows server 2019, my pg is pg13), and I created the plpython3u language.

I tried some simple script to test plpython3u, everything looks so fine. In fact, I want to connect to mssql to synchronize data between pg and sqlserver, so I installed pymssql package by pip command.

I can successfullly create the function, but cannot call it normally. Below is my script:

create or replace function public._py_sync_mspg()
  returns bigint
  language plpython3u
  cost 100
  volatile 
as $body$
import pymssql
conn = pymssql.connect('mssql host', 'ms user', 'mssql password', "database")
cursor = conn.cursor(as_dict=True)  

cursor.execute('select fitemid,fname from t_empl_detail where fname=%s', 'someone')
for row in cursor:
    print("ID=%d, Name=%s" % (row['fitemid'], row['fname']))

conn.close()
$body$;

alter function public._py_sync_mspg()
    owner to postgres;

I can create the function, But I can not call the function!

Below is the error message:

The application has lost the database connection: ⁃ If the connection was idle it may have been forcibly disconnected. ⁃ The application server or database server may have been restarted. ⁃ The user session may have timed out. Do you want to continue and establish a new session?

Below is the error captured image:

the error capture

I ever encountered the error for could not load some dll, I solved it. I ever thought that the import clause could not be used, I tried import os, that's ok. Now the current error completely stopped my hope to connect to SQLServer.

What's wrong?

Waiting for your help, thanks very much.