[python] Tkinter understanding mainloop

Till now, I used to end my Tkinter programs with: tk.mainloop(), or nothing would show up! See example:

from Tkinter import *
import random
import time

tk = Tk()
tk.title = "Game"
tk.resizable(0,0)
tk.wm_attributes("-topmost", 1)

canvas = Canvas(tk, width=500, height=400, bd=0, highlightthickness=0)
canvas.pack()

class Ball:
    def __init__(self, canvas, color):
        self.canvas = canvas
        self.id = canvas.create_oval(10, 10, 25, 25, fill=color)
        self.canvas.move(self.id, 245, 100)
    def draw(self):
        pass

ball = Ball(canvas, "red")

tk.mainloop()

However, when tried the next step in this program (making the ball move by time), the book am reading from, says to do the following. So I changed the draw function to:

def draw(self):
    self.canvas.move(self.id, 0, -1)

and add the following code to my program:

while 1:
    ball.draw()
    tk.update_idletasks()
    tk.update()
    time.sleep(0.01)

But I noticed that adding this block of code, made the use of tk.mainloop() useless, since everything would show up even without it!!!

At this moment I should mention that my book never talks about tk.mainloop() (maybe because it uses Python 3) but I learned about it searching the web since my programs didn't work by copying book's code!

So I tried doing the following that would not work!!!

while 1:
    ball.draw()
    tk.mainloop()
    time.sleep(0.01)

What's going on? What does tk.mainloop()? What does tk.update_idletasks() and tk.update() do and how that differs from tk.mainloop()? Should I use the above loop?tk.mainloop()? or both in my programs?

while 1:
    root.update()

... is (very!) roughly similar to:

root.mainloop()

The difference is, mainloop is the correct way to code and the infinite loop is subtly incorrect. I suspect, though, that the vast majority of the time, either will work. It's just that mainloop is a much cleaner solution. After all, calling mainloop is essentially this under the covers:

while the_window_has_not_been_destroyed():
    wait_until_the_event_queue_is_not_empty()
    event = event_queue.pop()
    event.handle()

... which, as you can see, isn't much different than your own while loop. So, why create your own infinite loop when tkinter already has one you can use?

Put in the simplest terms possible: always call mainloop as the last logical line of code in your program. That's how Tkinter was designed to be used.

I'm using an MVC / MVA design pattern, with multiple types of "views". One type is a "GuiView", which is a Tk window. I pass a view reference to my window object which does things like link buttons back to view functions (which the adapter / controller class also calls).

In order to do that, the view object constructor needed to be completed prior to creating the window object. After creating and displaying the window, I wanted to do some initial tasks with the view automatically. At first I tried doing them post mainloop(), but that didn't work because mainloop() blocked!

As such, I created the window object and used tk.update() to draw it. Then, I kicked off my initial tasks, and finally started the mainloop.

import Tkinter as tk

class Window(tk.Frame):
    def __init__(self, master=None, view=None ):
        tk.Frame.__init__( self, master )
        self.view_ = view       
        """ Setup window linking it to the view... """

class GuiView( MyViewSuperClass ):

    def open( self ):
        self.tkRoot_ = tk.Tk()
        self.window_ = Window( master=None, view=self )
        self.window_.pack()
        self.refresh()
        self.onOpen()
        self.tkRoot_.mainloop()         

    def onOpen( self ):        
        """ Do some initial tasks... """

    def refresh( self ):        
        self.tkRoot_.update()