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

160 Chapter 7

This is fine, because the program keeps running even while it’s lis-

tening for mouse clicks, so by the time the user clicks for the first

time, the screen and pen are correctly colored and sized, as shown

in Figure 7-4.

Figure 7-4: A drawing I produced by clicking a few

times with TurtleDrawMax.py

Using the setpos() function as the callback for turtle

.onscreenclick(), we’ve built a fun paint program that interacts

with the user when they click the mouse by drawing lines to

wherever they click. Try customizing the app with different colors,

widths, or anything else you can think of to make it your own.

Listening for Keyboard Events: ArrowDraw

With our turtle drawing program, we saw how listening for mouse

clicks can make the user feel like they’re more in control of the

program. In this section, we’ll learn to use keyboard interaction

to give the user even more options. We’ll also define our own func-

tions to use as event handlers.

In the TurtleDraw.py program, we passed t.setpos as the

callback function to tell the computer what to do when an

onscreenclick() event happened; we wanted to set the turtle’s