from queue import Queue
from threading import Thread
import tkinter

#these three are just for the example and don't need to be in your real code.
import random
import time
import datetime

#this collection facilitates inter-thread communication.
#the worker thread pushes status messages to it,
#and the gui thread gets those messages and displays them.
messages = Queue()

def get_temperature():
    #pretend that this function gets the temperature from a thermometer peripheral or a weather website or something.
    return random.randint(40, 90)

def check_temperature_forever():
    """
    Checks the temperature every second and pushes that data into the messages queue.
    This loops forever and never returns, so it's best run in its own thread.
    """
    while True:
        time.sleep(1)
        temp = get_temperature()
        message = "{} - the temperature is {} degrees F".format(datetime.datetime.now(), temp)
        messages.put(message)

def on_idle():
    """whenever the window isn't busy with another task, see if there are any new messages to display."""

    #check for messages
    if not messages.empty():
        message = messages.get()
        #display the message
        label.config(text=message)

    #call this function again the next time the window isn't busy
    root.after_idle(on_idle)

#set up window
root = tkinter.Tk()
label = tkinter.Label(root)
label.pack()

#start thread. use `daemon=True` if you want the thread to terminate when the user closes the window.
t = Thread(target=check_temperature_forever, daemon=True)
t.start()

#wait until the window is ready to be displayed.
#If we don't do this, then `on_idle` will call itself over and over forever,
#because the window counts as "not busy" if it isn't visible yet.
root.wait_visibility()

#register idle event
root.after_idle(on_idle)

#start the GUI's event loop, which will never return as long as the window is open
root.mainloop()