Build a complete game with Python and PyGame

The run Function

The run function is the main PyGame event loop. On line 145, I initialize running to True. This is the loop control variable. When I want to exit, all I have to do is set running to False. You might think about just calling break, but it won't work here because lines 146 and 147 are nested loops; break would just exit one level, and the outer loop would restart the inner loop. Setting running to False makes the outer loop exit and the loop ends.

Line 147 gets all of the events from the PyGame event queue and iterates over them. Line 148 checks whether the event type is pygame.KEYDOWN; that is, has the player pressed a key? If so, then the if/elif statements on lines 149, 153, 157, 161, 165, 170, 175, and 180 find the key, determine the direction, and update self.playerX, self.playerY, and self.grid accordingly.

The elif event.key == ord ( "t" ) on line 185 handles the request for a teleport; self.grid is cleared as in all the other moves, but instead of incrementing or decrementing self.playerX and self.playerY, new random values are generated.

Line 190 checks whether the player has pressed the p key, which is the "quit" key. If so, then running is set to False (line 191) so the main loop will exit. See the "Why p?" box for an explanation of why the number pad wasn't used.

Line 192 calls self.moveBots after the player's move has been processed, which makes all of the robots move toward the player. Line 193 uses the self.checkWinLose function to see if the game is over. If so, lines 194 through 197 print the appropriate message and end the loop. Finally, line 203 calls self.drawGrid to draw all of the changes to the screen.

Overall Program Setup

Up to this point, I've defined functions but, until the class itself and all of its requirements are set up, it won't do anything. So, other than placing the class and a couple of modules into memory, nothing happens until line 205. There, I initialize PyGame, and on line 206 create the screen variable by setting the PyGame window size to 1024x768.

Line 208 is where the robotsGame class gets initialized; the first argument is the PyGame screen (so the class can draw things) and the number of robots to place on the grid. Line 209 calls the game's drawGrid function, then line 210 starts the main event loop, game.run, which will continue until the game is over.