Teach Your Kids To Code: A Parent-friendly Guide to Python Programming

72 Chapter 4

You’ll notice the one drawback to nested loops while you’re

waiting for this program to run: the shapes shown in Figure 4-7

take longer to draw than our simple spirals did. That’s because

we’re performing so many more steps than we did with our

simple spirals. In fact, when we draw the six-sided version of our

ViralSpiral.py, the final drawing consists of 2,352 separate lines!

All those drawing commands, plus the turning and setting the

pen color, add up to a lot of work, even for a fast computer. Nested

loops are useful, but remember that

the extra steps can slow our programs

down, so we use nested loops only

when the effect is worth the wait.

Here’s the completed code for

ViralSpiral.py.

ViralSpiral.py

import turtle

t = turtle.Pen()

t.penup()

turtle.bgcolor("black")

# Ask the user for the number of sides, default to 4, min 2, max 6

sides = int(turtle.numinput("Number of sides",

"How many sides in your spiral of spirals? (2-6)", 4,2,6))

colors = ["red", "yellow", "blue", "green", "purple", "orange"]

# Our outer spiral loop

for m in range(100):

t.forward(m*4)

position = t.position() # Remember this corner of the spiral

heading = t.heading() # Remember the direction we were heading

print(position, heading)

# Our "inner" spiral loop

# Draws a little spiral at each corner of the big spiral

for n in range(int(m/2)):

t.pendown()

t.pencolor(colors[n%sides])

t.forward(2*n)

t.right(360/sides - 2)

t.penup()

t.setx(position[0]) # Go back to the big spiral's x location

t.sety(position[1]) # Go back to the big spiral's y location

t.setheading(heading) # Point in the big spiral's heading

t.left(360/sides + 2) # Aim at the next point on the big spiral