6.9: Checking for Keyboard Presses

           elif event.type == KEYDOWN:
                if event.key == K_q:
                    clickedButton = YELLOW
                elif event.key == K_w:
                    clickedButton = BLUE
                elif event.key == K_a:
                    clickedButton = RED
                elif event.key == K_s:
                    clickedButton = GREEN

Lines 1 [85] to 9 [93] check for any KEYDOWN events (created when the user presses a key on the keyboard). The Q, W, A, and S keys correspond to the buttons because they are arranged in a square shape on the keyboard.

The Q key is in the upper left of the four keyboard keys, just like the yellow button on the screen is in the upper left, so we will make pressing the Q key the same as clicking on the yellow button.

We can do this by setting the clickedButton variable to the value in the constant variable YELLOW. We can do the same for the three other keys. This way, the user can play Simulate with either the mouse or keyboard.