A List of Objects

Part of the Sprites and Images section of Coddy's Pygame journey. Lesson 13 of 36.

Two named stars is not a sky. Forty need a list: make the objects in a loop and append each one.

stars = []
for i in range(40):
    x = random.randint(0, 639)
    y = random.randint(0, 479)
    speed = random.randint(1, 3)
    stars.append(Star(x, y, speed))

Then one loop updates them all and another draws them all:

for star in stars:
    star.update()

Inside the for, star is each object in turn, so star.update() moves that star by its own speed. Adding a hundred more stars changes one number; the update and draw code stays the same.

Make the list once, before the game loop. A list made inside the loop is a new list of new stars every frame, all back at their starting places, so nothing ever moves.

Challenge

Medium

Add import random at the top.
Before the loop, make stars: a list of 40 Star objects, each with a random x from 0 to 639, a random y from 0 to 479 and a random speed from 1 to 3.
In the loop, update every star in stars, and draw every star after the fill. Remove slow and fast.

Try it yourself

import pygame

pygame.init()
screen = pygame.display.set_mode((640, 480))
pygame.display.set_caption("Falling Stars")
clock = pygame.time.Clock()

class Star:
    def __init__(self, x, y, speed):
        self.x = x
        self.y = y
        self.speed = speed

    def update(self):
        self.y += self.speed
        if self.y > 480:
            self.y = 0

    def draw(self, screen):
        pygame.draw.circle(screen, (255, 255, 255), (self.x, self.y), 4)


slow = Star(200, 0, 1)
fast = Star(440, 0, 3)

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

    slow.update()
    fast.update()

    screen.fill((20, 22, 40))
    slow.draw(screen)
    fast.draw(screen)
    pygame.display.flip()
    clock.tick(60)

pygame.quit()