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

Loops Are Fun (You Can Say That Again) 61

Run the program and try your own numbers. You can even

make a rosette of 90 circles, or 200 (but you’ll be waiting a while

as Python draws that many circles!). Customize the program to

make it your own: change the background color or the rosette

color, make the circles bigger or smaller, or make them bigger and

smaller! Play with your programs as you create them and as you

think of fun things you’d like them to do. Figure 4-4 shows what

my five-year-old son, Alex, dreamed up by adding just three extra

lines of code to RosetteGoneWild.py. Go to http://www.nostarch

.com/teachkids/ for the source code.

Game Loops and while Loops

The for loop is powerful, but there are limits to its power. For

instance, what if we wanted to stop our loop when some event

occurred, instead of going all the way through a long list of num-

bers? Or what if we weren’t sure how many times to run our loop?

For example, consider a game loop—when we write a pro-

gram, especially a game, where the user gets to choose whether

to keep playing or to quit. We, as programmers, can’t know in

advance how many times users will choose to play our game or

Figure 4-3: A user-defined rosette of
30 circles

Figure 4-4: A little imagination and a touch

of code can turn our rosette program into a

lot of colorful fun!