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

168 Chapter 7

Whatever kinds of apps you want to build, you’re probably going

to rely on user interaction to drive the experience. Think of the

games or other apps that you spend the most time playing: what

they all have in common is that you have some kind of control over

what happens and when. Whether you’re moving a paddle to hit a

ball; pressing the mouse button or touching and dragging to fire

something through the air; or clicking, swiping, and tapping to clear

a screen, you’re generating user events—and the programs you love

handle those events by doing something cool. Let’s build one more

interactive app for practice, and then we’ll build even more of the

kinds of apps we play with every day.

c ickKaleidoscopel

Let’s combine our ability to create functions and our ability to

handle interactive clicks to create an interactive kaleidoscope.

The user will be able to click anywhere on the screen, and four

reflected spirals of a random shape and color will be drawn start-

ing from the point where the user clicked. The result will look like

our Kaleidoscope.py program from page 134, but the user will be

able to create their own unique patterns using this kaleidoscope.

The draw_kaleido() Function

Let’s talk about the challenges in building a customized kalei-

doscope program. We know we want to allow the user to click

the screen to begin the drawing process, so we’ll use the turtle

.onscreenclick() function from the previous section. We know that

this function will give us an (x, y) location on the screen that we

can use in our callback function. And we can look back at our orig-

inal kaleidoscope program to see that all we have to do is draw a

spiral at each of the four points (x, y), (–x, y), (–x, –y), and (x, –y) to

achieve the desired reflection effect.

Each of our four reflected spirals should be the same color and

size to create the mirror illusion. We will call our function draw_

kaleido() and define it as follows:

u def draw_kaleido(x,y):

v t.pencolor(random.choice(colors))

w size = random.randint(10,40)

draw_spiral(x,y, size)