from time import sleep
from threading import Thread
import tkinter as tk
from queue import Queue


class Backend(Thread):

    def __init__(self, queue, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.queue = queue

    def run(self):
        self.queue.put('ready')
        for n in range(1, 5):
            self.queue.put(f'stage {n}')
            print(f'stage {n}')
            sleep(2)
        self.queue.put('done')


class App(tk.Tk):

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.status = tk.StringVar(self, value='ready')
        tk.Label(self, textvariable=self.status).pack()

        tk.Button(self, text="Run process", command=self.go).pack()
        self.queue = Queue()

    def go(self):
        p = Backend(self.queue)
        p.start()
        self.after(100, self.check_queue)

    def check_queue(self):
        if not self.queue.empty():
            self.status.set(self.queue.get())
        if self.status.get() != 'done':
            self.after(100, self.check_queue)

App().mainloop()