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

218 Chapter 9

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

pygame.display.set_caption("Smiley Explosion")

mousedown = False

keep_going = True

clock = pygame.time.Clock()

pic = pygame.image.load("CrazySmile.bmp")

colorkey = pic.get_at((0,0))

pic.set_colorkey(colorkey)

u sprite_list = pygame.sprite.Group()

The setup looks like SmileyBounce2.py, but we’re adding a

variable called sprite_list at u that will contain our group of

smiley face sprites. Storing the sprites in a Group will make it

faster and easier to do things like draw all the smileys on the

screen every frame, move all the smileys for each step of the ani-

mation, and even check to see if the smiley sprites are colliding

with objects or with one another.

To create sprite objects for complex animations and games,

we will create our own Sprite class that extends, or builds on,

Pygame’s Sprite class, adding the variables and functions that we

want for our custom sprites. We’ll name our sprite class Smiley,

and we’ll add variables for the position of each smiley (pos), its

x- and y-velocity (xvel and yvel; remember velocity is another word

for speed), and its scale, or how big each smiley will be (scale):

class Smiley(pygame.sprite.Sprite):

pos = (0,0)

xvel = 1

yvel = 1

scale = 100

Our Smiley class definition starts with the keyword class,

followed by the name we want for our class, plus the type we’re

extending (pygame.sprite.Sprite).

s tting Up e sprites

The next step after starting our Smiley class and listing the data

variables that we’d like each smiley sprite object to remember is

called initialization, sometimes also referred to as the constructor

for our class. This will be a special function that is called every

time a new object of our Smiley class is created, or constructed, in

our program. Just like initializing a variable gives it a starting

value, the initialization function, __init__(), in our Smiley class will