How to update python tkinter window

Question

I'm currently trying to update a TKinter window every second. So the idea is that is should open a window, let python updates the field, show updated window. The situation right now is that the second window is only showing when i close the first one. I'm guessing this has something to do with mainloop(). I looked into .update() and .update_idletasks() but I can't figure out how to implement it. TKinter is used to show a field with houses in it. So in general is should do this:

• Generate house location (already implemented)
• Show field with houses in it (already implemented)
• Generate new location of houses (already implemented)
• Show updated field

This is my current code. I'm not sure if the update function is necessary.

    class Plot(tk.Frame):
        def __init__(self, master=None):
            tk.Frame.__init__(self, master)
            self.grid()

        def createWidgets(self, list_houses):
            houses = list_houses
            self.w = tk.Canvas(self, width = field.width*SIZE, height = field.height*SIZE, bg = '#E4E4E4')

            ...

            self.w.grid()

        def update(self):
            ?

#GENERATES FIELD AND HOUSES
...

#PRINT FIRST WINDOW
plot = Plot()
plot.createWidgets(houses) <- PUT HOUSES IN TK INTER
plot.master.title('map of houses')
plot.mainloop()

# UPDATE FIELD <- THIS PART IS ONLY EXECUTED WHEN I CLOSE THE FIRST WINDOW, WHY?
i = 0
while i < 2:
    update = field.update_houses(houses) <- GENERATES NEW LOCATION OF HOUSES

    #PRINT UPDATED WINDOW, IT SHOULD BE PRINTED IN THE SAME WINDOW!
    plot = Plot()
    plot.createWidgets(houses) <- PUT HOUSES IN TKINTER
    plot.master.title('map of houses')

    i += 1

Thanks in advance!

Answer 1

Your update field is only executed when you close the window because tkinter's mainloop keeps running until the window is closed. Because of this mainloop, using a (long) while loop in tkinter is a bad idea, because the while loop locks up the tkinter mainloop.

To do something multiple times without blocking the mainloop, use the after method. This calls a function after a certain amount of time. You can call it once before entering your mainloop and then call it again in your update function, so that the update function calls itself. Take a look at this small example which uses after to execute an update function every second:

import Tkinter as tk
import random

def update():
    l.config(text=str(random.random()))
    root.after(1000, update)

root = tk.Tk()
l = tk.Label(text='0')
l.pack()
root.after(1000, update)
root.mainloop()

Answer 2

you could use the .update to the window. That would make it update the window and allow everything to be on it.