Pygame Sprite and Group Classes Explained

Once a game has more than a few things moving, each one needs its picture, its position and its behavior kept together. pygame.sprite.Sprite is a class for exactly that, and pygame.sprite.Group manages many of them at once.

A sprite is a class that inherits Sprite and sets two attributes, image and rect:

import random
import pygame

pygame.init()
screen = pygame.display.set_mode((480, 360))
clock = pygame.time.Clock()


class Coin(pygame.sprite.Sprite):
    def __init__(self):
        super().__init__()
        self.image = pygame.image.load("assets/images/coin.png").convert_alpha()
        self.rect = self.image.get_rect(center=(random.randint(20, 460), -20))
        self.speed = random.randint(2, 5)

    def update(self):
        self.rect.y += self.speed
        if self.rect.top > 360:
            self.kill()


coins = pygame.sprite.Group()
frame = 0
running = True

while running:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False

    frame += 1
    if frame % 20 == 0:
        coins.add(Coin())

    coins.update()

    screen.fill((30, 40, 70))
    coins.draw(screen)
    pygame.display.flip()
    clock.tick(60)

pygame.quit()

Coins appear at the top, fall and remove themselves at the bottom. The loop never deals with one coin at a time: coins.update() moves all of them and coins.draw(screen) draws all of them.

The Sprite class

Three rules:

1. Call super().__init__() first in __init__.
2. Set self.image to a Surface (a loaded image, or one you drew).
3. Set self.rect to its position, usually self.image.get_rect(...).

Put the sprite's behavior in update(). Group.update() passes along any arguments you give it, so group.update(dt) hands every sprite the delta time.

Group methods

A sprite can be in several groups at once. A common layout is one group with everything (for drawing) plus groups by role (enemies, bullets, coins) for collisions.

A player sprite

The player is a sprite too. Its update() reads the keyboard:

import pygame

pygame.init()
screen = pygame.display.set_mode((480, 360))
clock = pygame.time.Clock()


class Player(pygame.sprite.Sprite):
    def __init__(self, pos):
        super().__init__()
        self.right = pygame.image.load("assets/images/player.png").convert_alpha()
        self.left = pygame.transform.flip(self.right, True, False)
        self.image = self.right
        self.rect = self.image.get_rect(center=pos)

    def update(self):
        keys = pygame.key.get_pressed()
        dx = keys[pygame.K_RIGHT] - keys[pygame.K_LEFT]
        dy = keys[pygame.K_DOWN] - keys[pygame.K_UP]
        self.rect.move_ip(dx * 4, dy * 4)
        self.rect.clamp_ip(screen.get_rect())
        if dx < 0:
            self.image = self.left
        elif dx > 0:
            self.image = self.right


class Enemy(pygame.sprite.Sprite):
    def __init__(self, x, y):
        super().__init__()
        self.image = pygame.image.load("assets/images/slime.png").convert_alpha()
        self.rect = self.image.get_rect(center=(x, y))
        self.speed = 2

    def update(self):
        self.rect.x += self.speed
        if self.rect.left < 0 or self.rect.right > 480:
            self.speed = -self.speed


player = Player((240, 300))
enemies = pygame.sprite.Group(Enemy(80, 80), Enemy(300, 160))
all_sprites = pygame.sprite.Group(player, *enemies)
running = True

while running:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False

    all_sprites.update()

    screen.fill((60, 120, 80))
    all_sprites.draw(screen)
    pygame.display.flip()
    clock.tick(60)

pygame.quit()

Press Play, click the game and walk with the arrow keys. The player faces the way it walks; the slimes patrol back and forth. Adding a third slime is one more Enemy(...). Sprite collisions makes them dangerous.

Other group types

Load an image once and share it when you make many sprites of the same kind; loading the file in every __init__, as the coin example does, is fine for a few sprites but slows a game that spawns hundreds.