In this chapter, we’ll finish building Alien Invasion. We’ll add a Play button to start the game on demand and to restart the game once it ends. We’ll also change the game so it speeds up when the player moves up a level, and we’ll implement a scoring system. By the end of the chapter, you’ll know enough to start writing games that increase in difficulty as a player progresses and that feature complete scoring systems.

Adding the Play Button

In this section, we’ll add a Play button that appears before a game begins and reappears when the game ends so the player can play again.

Right now, the game begins as soon as you run alien_invasion.py ...