from tkinter import * # Import tkinter

class CanvasDemo:
    def __init__(self):
        window = Tk() # Create a window
        window.title("Canvas Demo") # Set title

        # Place self.canvas in the window
        self.canvas = Canvas(window, width = 500, height = 200,
            bg = "white")
        self.canvas.pack()

        # Place buttons in frame
        frame = Frame(window)
        frame.pack()
        btBigger = Button(frame, text = "Bigger",
           command = self.increaseCircle)
        btSmaller = Button(frame, text = "Smaller",
           command = self.decreaseCircle)

        btClear = Button(frame, text = "Clear",
            command = self.clearCanvas)
        btBigger.grid(row = 1, column = 1)
        btSmaller.grid(row = 1, column = 2)
        btClear.grid(row = 1, column = 7)

        window.mainloop() # Create an event loop

    def increaseCircle(self):
        self.canvas.delete("oval")
        global radius
        if radius < 100:
            radius += 2
        self.canvas.create_oval(100 - radius, 100 - radius,
                           100 + radius, 100 + radius, tags = "oval")

    def decreaseCircle(self):
        self.canvas.delete("oval")
        global radius
        if radius > 2:
            radius -= 2
        self.canvas.create_oval(100 - radius, 100 - radius,
                           100 + radius, 100 + radius, tags = "oval")

        self.canvas = Canvas(window, bg = "white", width = 200, height = 200)
        canvas.pack()
        radius = 50
        self.canvas.create_oval(100 - radius, 100 - radius,
                           100 + radius, 100 + radius, tags = "oval")

    # Bind canvas with mouse events
        self.canvas.bind(btBigger, increaseCircle)
        self.canvas.bind(btSmaller, decreaseCircle)

        # Clear drawings
    def clearCanvas(self):
            self.canvas.delete("oval")

CanvasDemo() # Create GUI