H a n d s o n, p r o j e c t b a s e d

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try it yourSelF
12-6. Sideways Shooter:
Write a game that places a ship on the left side of the 
screen and allows the player to move the ship up and down. Make the ship fire 
a bullet that travels right across the screen when the player presses the space-
bar. Make sure bullets are deleted once they disappear off the screen.
Summary
In this chapter, you learned to make a plan for a game and learned the basic 
structure of a game written in Pygame. You learned to set a background color 
and store settings in a separate class where you can adjust them more easily. 
You saw how to draw an image to the screen and give the player control over 
the movement of game elements. You created elements that move on their 
own, like bullets flying up a screen, and deleted objects that are no longer 
needed. You also learned to refactor code in a project on a regular basis to 
facilitate ongoing development.
In Chapter 13, we’ll add aliens to Alien Invasion. By the end of the 
chapter, you’ll be able to shoot down aliens, hopefully before they reach 
your ship!

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13
A l i e n s !
In this chapter, we’ll add aliens to Alien 
Invasion. We’ll add one alien near the top 
of the screen and then generate a whole
fleet of aliens. We’ll make the fleet advance 
sideways and down, and we’ll get rid of any aliens hit 
by a bullet. Finally, we’ll limit the number of ships a 
player has and end the game when the player runs
out of ships.
As you work through this chapter, you’ll learn more about Pygame 
and about managing a large project. You’ll also learn to detect collisions 
between game objects, like bullets and aliens. Detecting collisions helps you 
define interactions between elements in your games: for example, you can 

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Chapter 13
confine a character inside the walls of a maze or pass a ball between two 
characters. We’ll continue to work from a plan that we revisit occasionally 
to maintain the focus of our code-writing sessions.
Before we start writing new code to add a fleet of aliens to the screen, 
let’s look at the project and update our plan.