Chapter 15 - Recursion - Programming Exercises - Page 525: 15.17

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# 15.17 (Tkinter: Sierpinski triangle) Revise Listing 15.9 to let the user use leftmouse/ # right-mouse clicks to increase/decrease the current order by 1. The initial # order is 0. from tkinter import * # Import tkinter class SierpinskiTriangle: def __init__(self): window = Tk() # Create a window window.title("Sierpinski Triangle") # Set a title self.width = 200 self.height = 200 self.canvas = Canvas(window, width=self.width, height=self.height) self.canvas.pack() # Add a label, an entry, and a button to frame1 frame1 = Frame(window) # Create and add a frame to window frame1.pack() self.order = 0 self.display() self.canvas.bind("", self.increaseOrder) self.canvas.bind("", self.decreaseOrder) window.mainloop() # Create an event loop def display(self): self.canvas.delete("line") p1 = [self.width / 2, 10] p2 = [10, self.height - 10] p3 = [self.width - 10, self.height - 10] self.displayTriangles(int(self.order), p1, p2, p3) def displayTriangles(self, order, p1, p2, p3): if order == 0: # Base condition # Draw a triangle to connect three points self.drawLine(p1, p2) self.drawLine(p2, p3) self.drawLine(p3, p1) else: # Get the midpoint of each triangle's edge p12 = self.midpoint(p1, p2) p23 = self.midpoint(p2, p3) p31 = self.midpoint(p3, p1) # Recursively display three triangles self.displayTriangles(order - 1, p1, p12, p31) self.displayTriangles(order - 1, p12, p2, p23) self.displayTriangles(order - 1, p31, p23, p3) def drawLine(self, p1, p2): self.canvas.create_line( p1[0], p1[1], p2[0], p2[1], tags="line") # Return the midpoint between two points def midpoint(self, p1, p2): p = 2 * [0] p[0] = (p1[0] + p2[0]) / 2 p[1] = (p1[1] + p2[1]) / 2 return p def increaseOrder(self, event): self.order += 1 self.display() def decreaseOrder(self, event): if self.order > 0: self.order -= 1 self.display() SierpinskiTriangle() # Create GUI