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

166 Chapter 7

t king a it one step Further:

clickandsmile

Let’s extend this interactive app by making one more change.

Instead of drawing a spiral, say we want to draw a smiley face

wherever the user clicks the mouse on the drawing screen.

The code will look a lot like our RandomSmileys.py program

from page 151, but instead of a loop that draws 50 smiley faces

at random locations on the screen, this program will handle the

mouse click event by drawing a smiley at the location the user

chooses, as many or as few times as the user wishes to click.

In fact, because our draw_smiley() function already takes two

parameters (the x- and y-coordinates of the location where we

wish to draw the smiley face), the code for ClickAndSmile.py is

identical to RandomSmileys.py, except for the last section. Just

replace the for loop that draws 50 random smileys with a call

to turtle.onscreenclick(draw_smiley). Remember how the turtle

.onscreenclick() function allows us to pass the name of a function

(like setpos) as the event handler for mouse clicks? We can pass

it draw_smiley so that when the user clicks, our draw_smiley() func-

tion will do its work at the location of the click. We do not include

draw_smiley’s parentheses, or any arguments, inside the parentheses

for turtle.onscreenclick().

ClickAndSmile.py

import random

import turtle

t = turtle.Pen()

t.speed(0)

t.hideturtle()

turtle.bgcolor("black")

def draw_smiley(x,y):

t.penup()

t.setpos(x,y)

t.pendown()

# Face

t.pencolor("yellow")

t.fillcolor("yellow")

t.begin_fill()

t.circle(50)

t.end_fill()

# Left eye

t.setpos(x-15, y+60)

t.fillcolor("blue")