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

Loops Are Fun (You Can Say That Again) 69

import turtle
t = turtle.Pen()
u t.penup()
turtle.bgcolor("black")

The first few lines of our program look like the other spirals

we’ve programmed, except that we won’t be drawing lines for the

big spiral. We plan to replace those with smaller spirals, so we

have a t.penup() at u to lift the turtle’s pen off the screen right

from the beginning. We then set the background color to black.

Keep typing: we’re not done! Next we’ll ask the user for the

number of sides they want using turtle.numinput(), with a default

of 4 if the user doesn’t choose something different, and we’ll restrict

the range of allowable sides to between 2 and 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"]

The turtle.numinput() function allows us to specify a title for

our input dialog; a prompt question; and default, minimum, and

maximum values, in that order: turtle.numinput(title, prompt,

default, minimum, maximum). Here, we specify a default value of 4 , a

minimum of 2 , and a maximum of 6. (If the user tries to enter 1

or 7 , for example, they’ll get a warning that the minimum allowed

value is 2 and the maximum allowed value is 6 .) We also set up our

colors list with six colors.

Next we’ll write our outer spiral loop. The outer loop will posi-

tion the turtle at each corner of the big spiral.

v for m in range(100):
t.forward(m*4)
w position = t.position() # Remember this corner of the spiral
x heading = t.heading() # Remember the direction we were heading

Our outer loop takes m from 0 to 99 for 100 total passes v. In

our outer loop, we move forward just like in our other spiral pro-

grams, but when we reach each corner of our big spiral, we stop to

remember our position w and heading x. The position is the turtle’s

(x, y) coordinate location on the screen, and the heading is the

direction the turtle is moving in.

Our turtle is taking a bit of a detour at every spot along the

large spiral in order to draw the smaller spirals, so it must return