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

178 Chapter 8

Type the following in a new IDLE window or download it from

http://www.nostarch.com/teachkids/:

ShowDot.py

import pygame

u pygame.init()

v screen = pygame.display.set_mode([800,600])

w keep_going = True

x GREEN = (0,255,0) # RGB color triplet for GREEN

radius = 50

y while keep_going:

z for event in pygame.event.get():

{ if event.type == pygame.QUIT:

keep_going = False

| pygame.draw.circle(screen, GREEN, (100,100), radius)

} pygame.display.update()

~ pygame.quit()

Let’s step through this program line by line. First, we import

the pygame module to gain access to its features. At u, we initialize

Pygame, or set it up for use. The command pygame.init() will need

to be called every time you want to use Pygame, and it always

comes after the import pygame command and before any other

Pygame functions.

At v, pygame.display.set_mode([800,600]) creates a display

window 800 pixels wide by 600 pixels tall. We store it in a vari-

able called screen. In Pygame, windows and graphics are called

surfaces, and the display surface screen is the main window where

all of our other graphics will be drawn.

At w, you might recognize our looping variable, keep_going:

we used this in our HighCard.py and FiveDice.py game loops in

Chapter 6 as a Boolean flag to tell our program to keep playing.

Here in our Pygame example, we use a game loop to continue

drawing the graphics screen until the user closes the window.

At x, we set up two variables, GREEN and radius, for use in

drawing our circle. The GREEN variable is set to the RGB triplet

value (0,255,0), a bright green. (RGB, or Red Green Blue, is one

of many ways to specify a color. To pick a color, you choose three

numbers, each between 0 and 255. The first number determines