Basic structure for a switch condition triggered by a GUI button, designed to change variable values within a while loop performing some set of instructions without the need for a dedicated tkinter window thread at the cost of strict concurrency of action

tkinter_while_loop_switch.py

import tkinter as tk

flag = False  # Global flag
idx = 0  # loop index

def switch():
    """Enable scanning by setting the global flag to True."""
    global flag
    flag = True

root = tk.Tk()
root.title("Switch GUI")

app = tk.Frame(root)
app.grid()

switch = tk.Button(app, text="Switch", command=switch)
switch.grid()

a_variable = "initial value"

while True:
    
    #some other set of instructions, for example, listening to a directory
    #and updating a_variable to a new directory to listen to
    if a_variable != "initial value":
        print("a_variable changed to ", a_variable)
    
    if idx % 500 == 0: #update every half second
        root.update()

    if flag:
        print("Button pressed")
        #switch some while loop variable values
        a_variable = "new value"
        flag = False
        
    idx += 1