Session 4: Pong :: CoderDojo Python & Pygame

Session 4: Coach notes

Mon, 01 Jan 0001 00:00:00 +0000

Goal of this session After the Basic checkpoint a ninja can: Explain what the pygame game loop is and how it differs from pgzrun. Make the ball move and bounce off the top and bottom edge and off both paddles. Understand what pygame.Rect is and how colliderect works. This is the first session with real pygame; expect confusion about the game loop. That’s normal. Preparation Starter ZIP ready. Test on the dojo laptop whether pygame is installed (not pgzero). Prepare a short explanation: “pgzrun did the loop for us. Now we do it ourselves.” Dojo Defender: ninjas migrate their project to pygame as well (the starter contains the basics). Schedule (3 hours) Time Activity 0:00 to 0:15 Looking back + explaining pygame vs pgzrun 0:15 to 0:45 Step 1 to 2: moving the ball + bouncing 0:45 to 1:30 Step 3: keeping score 1:30 to 2:00 Step 4: win condition + speed 2:00 to 2:30 Dojo Defender: pygame migration 2:30 to 2:50 Showcase: 1-vs-1 matches 2:50 to 3:00 Cliffhanger Common questions “The ball moves but disappears straight away” ball_dx and ball_dy are 0. The ninja hasn’t changed the starting values. Point at the line ball_dx, ball_dy = 0, 0.

Session 4: Cheatsheet

Mon, 01 Jan 0001 00:00:00 +0000

Pygame game loop import pygame, sys pygame.init() screen = pygame.display.set_mode((600, 400)) clock = pygame.time.Clock() running = True while running: clock.tick(60) for event in pygame.event.get(): if event.type == pygame.QUIT: pygame.quit(); sys.exit() # --- update --- # --- draw --- pygame.display.flip() Rectangle (Rect) paddle = pygame.Rect(x, y, breedte, hoogte) paddle.y -= 5 # moving paddle.colliderect(andere_rect) # collision → True/False Keyboard in pygame keys = pygame.key.get_pressed() if keys[pygame.K_w]: paddle.y -= 5 if keys[pygame.K_s]: paddle.y += 5 if keys[pygame.K_UP]: paddle.y -= 5 if keys[pygame.K_DOWN]: paddle.y += 5 Ball bounces off the walls if ball.top <= 0 or ball.bottom >= HEIGHT: ball_dy = -ball_dy Ball bounces off the paddle if ball.colliderect(paddle): ball_dx = -ball_dx Text in pygame font = pygame.font.SysFont(None, 48) txt = font.render(f"{score}", True, (255, 255, 255)) screen.blit(txt, (x, y)) Drawing a rectangle pygame.draw.rect(screen, (255, 255, 255), paddle) pygame.draw.ellipse(screen, (255, 220, 50), ball)

Session 4: Demo recording

Mon, 01 Jan 0001 00:00:00 +0000

Run the solution: cd code/sessions/04-pong/solution && uv run python main.py. Record ~10 seconds: play a few rallies and let the score go up. Save as pong.gif in static/sessions/04-pong/. Target size: ~600×400 pixels, ≤ 2 MB.