Code Snippet

#note - an ERROR may be caused as Python is complaining about breaking out of the while loop when the window is closed - you can ignore that for now (or a fix is provied in the solutions section for those who are interested"""
"""
==========Task===============

"""

from tkinter import *
import random
import time

class Ball: 
    def __init__(self,canvas,color): 
        self.canvas=canvas 
        self.id=canvas.create_oval(30,30,50,50,fill=color) 
        self.canvas.move(self.id,100,200)

        #ADD THESE LINES TO OUR __INIT__ METHOD
        self.x=0 #set the object variable x to 0 (don't move the ball horizontally)
        self.y=-1 #set the object variable y to -1 (this means keep moving the ball UP on initilisation)
        self.canvas_height=self.canvas.winfo_height() #set the canvas height by calling the canvas function winfo_height (it gives us the current canvas height)

    def draw(self): #to make the ball BOUNCE we change the draw function
        self.canvas.move(self.id,self.x,self.y) #change the call to the canvas's move function by passing the object variables x and y
        pos=self.canvas.coords(self.id) #create a variable called pos for position - do this by calling the canvas function coordinates
        #The above function would return the current x and y coordinates of anything drawn on the canvas as long as you know the identifying number
        #In this case it is the oval's identifier (self.id) that gives us the coordinates
        """ About the Coordinates
         1. coords function returns the coordinates as a list of four numbers
         [a,b,c,d] (e.g. 255,20,280,50)
         First two numbers = top left coordinates of the oval that are x1 and y1
         Last two numbers = bottom right x2 and y2 coordinates
        """

        if pos[1] <=0: #if you hit the top of the screen then stop subtracting 1 as defined in the __init__ method and therefore stop moving up -reverse directions
            self.y=1
        if pos[3] >=self.canvas_height: #if the bottom coordinates are greater or equal to canvas height, then reverse again, and set y back to -1 (go up)
            self.y=-1
        

def main():
    tk=Tk()
    tk.title("My 21st Century Pong Game")
    tk.resizable(0,0)
    tk.wm_attributes("-topmost",1)
    canvas=Canvas(tk,bg="white",width=500,height=400,bd=0,highlightthickness=0)
    canvas.pack()
    tk.update()

    ball1=Ball(canvas,'green')
    while 1:
        tk.update()
        ball1.draw() #call the ball draw method here
        time.sleep(0.01)
main()




                    

Try it yourself