pygame — real-time applications

You will be able to

• ✓ Describe the game loop: events → update → draw
• ✓ Keep physics/rules out of the draw call
• ✓ Know surfaces, clocks and event types at a reading level

The loop is the application

Web apps wait for a request. Games poll. clock.tick(60) aims at 60 frames per second. If your update does a pandas groupby on 100,000 rows inside that loop, the game stutters. Heavy data work belongs in a pipeline that writes a small table the game then reads — or in a loading screen, once.

pygame.QUIT is not optional. Without it, the window’s close button does nothing useful and students force-kill Python. Always handle QUIT and a key for escape.

State is a dict (or a class)

player = {"x": 40, "y": 80, "vx": 3} is enough for a first sprite. Each frame: x = x + vx, bounce when x hits a wall. Classes (pygame.sprite.Sprite) are this dict with methods and a rect for collisions. Learn the dict first so Sprite is not magic.

Collision is geometry: two rectangles overlap. pygame.Rect.colliderect is the helper. The rule “if they overlap, score += 1” is a pure function of two rects if you keep it out of the blit (draw) section.

Draw is the last step, not the program

fill the screen (or you see smears), blit images, flip/update the display. Mixing “load CSV” into the draw section is how a 60 FPS loop becomes a 2 FPS slide show. Load assets once before the loop.

Fonts, sounds and images are files. pathlib belongs here too. A missing .png should raise a clear error at startup, not a black rectangle after the principal sits down.

What pygame is for — and not for

For: 2D games, interactive lab sims, quiz kiosks, simple robot visualisations. Not for: Excel reports (pandas), websites (Flask/Django/FastAPI), numeric HPC (NumPy/SciPy). Real products combine them: a pygame trainer that saves scores to SQLite and a pandas weekly report.

Words that matter

Game loop

Repeated cycle: events, update state, draw.

Frame

One pass of that loop; FPS is frames per second.

Surface

An image buffer you blit onto the window.

Event

A queued input: key, mouse, quit, custom user event.

Common mistakes

On a full Python install — pygame

The usual Python library for 2D real-time apps in schools and indie games. Installs SDL under the hood.

pip install pygame

Minimal loop: quit, move a rect, bounce, draw. Copy this onto a laptop.

import pygame

pygame.init()
screen = pygame.display.set_mode((640, 360))
clock = pygame.time.Clock()
x, vx = 40, 4
running = True
while running:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False
    x = x + vx
    if x > 600 or x < 0:
        vx = -vx
    screen.fill((12, 12, 16))
    pygame.draw.rect(screen, (225, 6, 0), (x, 160, 40, 40))
    pygame.display.flip()
    clock.tick(60)
pygame.quit()

Example program — Eight frames of a bouncing x

The update half of a game loop. pygame draws this 60 times a second.

Your turn — Move then stop at the wall

Start x = 0, speed = 10. Loop 5 times adding speed. If x >= 40, set speed to 0. Print a line containing 40.

Self-assessment

Check your understanding before you mark the lesson complete.