Answer
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# 15.26 (Turtle: Koch snowflake fractal) Rewrite the Koch snowflake program in Exercise
# 15.25 using Turtle, as shown in Figure 15.15. Your program should prompt
# the user to enter the order and display the corresponding fractal for the order.
import turtle
import math
# Draw a snow flak with the specified order on one line
def displayKochSnowFlake(order, p1, p2):
if order == 0:
# Draw a line
drawLine(p1[0], p1[1], p2[0], p2[1])
else:
# Get points x, y, z on the edge
deltaX = p2[0] - p1[0]
deltaY = p2[1] - p1[1]
x = [p1[0] + deltaX / 3, p1[1] + deltaY / 3]
y = [p1[0] + deltaX * 2 / 3, p1[1] + deltaY * 2 / 3]
z = [((p1[0] + p2[0]) / 2 - math.cos(math.radians(30)) * (p1[1] - p2[1]) / 3),
(int)((p1[1] + p2[1]) / 2 - math.cos(math.radians(30)) * (p2[0] - p1[0]) / 3)]
# Recursively display snow flakes on lines
displayKochSnowFlake(order - 1, p1, x)
displayKochSnowFlake(order - 1, x, z)
displayKochSnowFlake(order - 1, z, y)
displayKochSnowFlake(order - 1, y, p2)
# Draw a line from (x1, y1) to (x2, y2)
def drawLine(x1, y1, x2, y2):
turtle.penup()
turtle.goto(x1, y1)
turtle.pendown()
turtle.goto(x2, y2)
def main():
p1 = [0, 175]
p2 = [-150, -75]
p3 = [150, -75]
order = eval(input("Enter an order: "))
displayKochSnowFlake(order, p1, p2)
displayKochSnowFlake(order, p2, p3)
displayKochSnowFlake(order, p3, p1)
turtle.done()
main()
