[Python] How to update a variable on live

I'm trying to use Tkinter in order to create a photon counter, but here I will use the time.time() to simulate the data constantly changing. I have tried to synthesize my code to find and easily reproduce the problem.

The goal is to have a class object from which a method creates a panel that shows the actual time as fast as possible. With the knowledge that later on I will close the panel to do other processes, so my code must continue to run after I close the window.

Here is my code:

import numpy as np
import matplotlib.pyplot as plt
import tkinter as tk
import time

class GUI:
def __init__(self, master : tk.Tk, string : str):
self.master = master
self.string = time.time()
master.title('A simple window')

self.label = tk.Label(master, text=self.string)
self.label.pack()


def update_text(self, string):
self.string = time.time()
self.label.config(text=self.string)

root=tk.Tk()
my_gui = GUI(root,"HOLA")

while 1:
my_gui.update_text(time.time())


my_gui.master.update_idletasks()
my_gui.master.update()

root.mainloop()


The code works very well in my opinion. But when I close the panel I get the error TclError: invalid command name ".!label".

I then tried another version with VarStr and I included my time variable at the beginning of my class (sorry if the description is unclear, but you can look at the code and it will be easier to understand):

class GUI:
def __init__(self, master : tk.Tk, value):
self.master = master

self.string=tk.StringVar()
self.string.set(value) #The textvariable already updates the label automatically when the StringVar changes.
master.title("A simple window")

self.label = tk.Label(master, textvariable=self.string)
self.label.pack()
self.label.after(1, self.update_text)


def update_text(self):
self.string.set(self.string)
self.label.after(1, self.update_text)

root=tk.Tk()
my_gui = GUI(root,time.time())

root.mainloop()


Now I don't get any Error in the log, but the panel no longer updates and only shows "PY_VAR". I also no longer have my infinite loop from which I get an updated time.time(), which was useful as in my real code I have loops upon loops in which in one of them my variable of interest is updated and when I finished with it I could just close the panel and then should be able to continue running my code.

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