Problems with script to view and eject users

I'm doing a script with python3 in linux to let me know when someone is connected to my system and allows me to throw the user I want. I have this script and it works with graphical interface with the tkinter library. The problem is that when I'm going to enter the user's tty in the four-letter variable and give it to send, the code of the delete function does not work (sudo pkill -9 -t nombreusuario) .

Also e tested with: subprocess.run("sudo pkill -9 -t {0}").format(nombreusuario)

1.I would like to know how to enter a python variable in a linux command so that in this case it can throw the user.

2.I also want to know if the way to save the result of an Entry that I do is fine. For example:

cuadrotexto=Entry() 
resultadoEntry=cuadrotexto.get()

Would that be like saving what I put in the text box in the resultEntry variable?

#! /usr/bin/python3
#-*- coding: utf-8 -*-

from tkinter import *
import subprocess
from tkinter import messagebox

a=subprocess.check_output("who|wc -l",shell=True)
b=int(a.decode("utf-8").strip())
lista=subprocess.check_output("who",shell=True)
lista2=subprocess.check_output('who| cut -d " " -f 1,4,6',shell=True)


def funelim():

  def elimiusr():

    subprocess.run("sudo pkill -9 -t nombreusuario")

 raiz=Tk()
 raiz.title("Eliminar usuario")
 raiz.resizable(0,0)
 raiz.geometry("380x150")

 texto=Label(raiz,text="Elige el tty del usuario que quieres eliminar")
 texto.grid(row=0,column=0,sticky="w")

 texto2=Label(raiz,text=lista2)
 texto2.grid(row=1,column=0,sticky="w",pady=10)

 cuadronombre=Entry(raiz)
 cuadronombre.grid(row=2,column=0,sticky="w")
 cuadronombre.config(justify="center")
 nombreusuario=cuadronombre.get()

 boton3=Button(raiz,text="Enviar",command=elimiusr)
 boton3.grid(row=2,column=0,sticky="e",padx=170)

 raiz.mainloop()


def elimus():

 if b>1:

    def exit():
        root.destroy()

    root=Tk()
    root.title("Alguien se a conectado al sistema")
    root.resizable(0,0)
    root.geometry("380x150")

    miLabel=Label(root,text="Alguien se a conectado al sistema, ¿Que quiere hacer?")
    miLabel.grid(row=0,column=0)
    miLabel2=Label(root,text=lista).grid(column=0,row=1,pady=10,sticky="w")

    boton1=Button(text="Elim.Usuario",command=funelim)
    boton1.grid(column=0,row=2,sticky="w")

    boton2=Button(text="Salir",command=exit)
    boton2.grid(column=0,row=2,sticky="e")
    root.mainloop()



  elimus()