[inconsistent output] subprocess.call to run cmd commands to get Kerberos ticket

[Yelin]

As part of my daily work, I need to run a couple of lines of commands in cmd prompt in order to get Kerberos ticket to a database. Here are the commands:

cd C:\ProgramData\MIT\Kerberos5\
"C:\Program Files\MIT\Kerberos\bin\kinit" -kt ossuser.keytab ossuser

I am now asked to make it more nicely, i.e., by making it as a button on a GUI (which contains many other function) developed using Tkinter. To do this, I try to use subprocess.call. Here are the commands:

Command_piece_1:

import subprocess
command_01='cd C:\ProgramData\MIT\Kerberos5'
command_02='"'+'C:\Program Files\MIT\Kerberos'+'\\'+'bin\kinit'+'"'+' -kt ossuser.keytab ossuser'
conn=subprocess.call(command_01+"&"+command_02, shell=True)

And here is my definition for the button before root = Tk():

Command_piece_2

import subprocess

def connect_impala():
    command_01='cd C:\ProgramData\MIT\Kerberos5'
    command_02='"'+'C:\Program Files\MIT\Kerberos'+'\\'+'bin\kinit'+'"'+' -kt ossuser.keytab ossuser'
    conn=subprocess.call(command_01+"&"+command_02, shell=True)
    if conn==0:
       messagebox.showinfo("INFO","Getting ticket successful.\nYou can close this INFO window.")
    else:
       messagebox.showerror("ERROR","Getting ticket failed!\nPlease check if your VPN is working properly and try again.")

Now strange thing happens. When I click the corresponding button on the GUI, it fails forever (showing the ERROR window I defined). However, when I try Command_piece_1 in IDLE, it succeeds.

Anyone knows how this can happen? Do I miss out something in the function definition?

Python version: 3.6.2
Tk version: 8.6.6
IDLE version: 3.6.2