Animates two balls that bounce on the screen.

animation_if.py

#import libraries
#Uses http://stackoverflow.com/questions/13215215/python-tkinter-animation
import tkinter

#Set width, height, frames per second and how long to cross
CANVAS_WIDTH = 800
CANVAS_HEIGHT = 600
FPS = 120
SECONDS_TO_CROSS = 1.5

#Ball class
#Used to draw and move ball on screen
class Ball(object):
    #initialize method
    #Precondition: canvas, arguments (x & y position),
    # keyword arguments (colour)
    #Postcondition: ball created and set in motion
    def __init__(self, canvas, *args, **kwargs):
        self.canvas = canvas
        self.id = canvas.create_oval(*args, **kwargs)
        self.vx = CANVAS_WIDTH/FPS/SECONDS_TO_CROSS
        self.vy = 0
    #move method
    #Precondition - gets current location
    #changes velocity based on if edge was hit
    #moves ball
    def move(self):
        x1, y1, x2, y2 = self.canvas.bbox(self.id)
        if x2 > CANVAS_WIDTH:
            self.vx = self.vx*-1
        if x1 < 0:
            self.vx = self.vx*-1
        self.canvas.move(self.id, self.vx, self.vy)

#App class
#controls the canvas and the objects displayed on it
class App(object):
    #Initalize method, sets everything up
     def __init__(self, master, **kwargs):
        self.master = master
        #Create the canvas - graphics will be drawn on it
        self.canvas = tkinter.Canvas(self.master, width = CANVAS_WIDTH, height = CANVAS_HEIGHT)
        #pack the canvas so it shows up
        self.canvas.pack()
        #Create a list of ball objects - note the variables
        self.balls = [
            Ball(self.canvas, 20, 260, 120, 360, outline = 'white', fill = 'blue'),
            Ball(self.canvas, 2, 2, 40, 40, outline = 'white', fill = 'gold'),
            ]
        #Set animation to start right away (after 0 milliseconds
        self.master.after(0, self.animation)

    #animation function
     def animation(self):
         #loop through all the balls on the screen and move them
         for ball in self.balls:
             ball.move()
         #set the timer to play again after the milliseconds have passed
         self.master.after(1000//FPS, self.animation)

#create the main window, start the app and run the mainloop
main_window = tkinter.Tk()
app = App(main_window)
main_window.mainloop()