Simple particles in pygame

particle_c_growing_01.py

import math
import random

import pygame

class Particle(pygame.sprite.Sprite):
    def __init__(self, x, y):
        super().__init__()
        self.start = (x, y)
        self.x = x
        self.y = y
        self.r = 0
        self.speed = random.randint(1, 5)

        self.image = pygame.Surface((self.r * 2, self.r * 2), pygame.SRCALPHA)
        self.rect = self.image.get_rect(center=(self.x, self.y))

    def update(self, dt):
        self.r += self.speed * dt / 400
        self.image = pygame.Surface((self.r * 2, self.r * 2), pygame.SRCALPHA)
        pygame.draw.circle(self.image, (192, 255, 255), (self.r, self.r), self.r, width=0)
        pygame.draw.circle(self.image, (0, 128, 128), (self.r, self.r), self.r, width=2)
        self.rect = self.image.get_rect(center=(self.x, self.y))


class PGMTest:
    WIDTH = 1280
    HEIGHT = 600
    def __init__(self):
        pass
    def prepare_window(self):
        self.screen = pygame.display.set_mode((self.WIDTH, self.HEIGHT))
        self.screen.fill((0, 0, 255))

    def prepare_particles(self, x, y, r):
        self.particles = pygame.sprite.Group()
        for i in range(100):
            angle = random.random() * math.pi * 2
            self.particles.add(Particle(x + math.sin(angle) * r, y + math.cos(angle) * r))

    def run(self):
        dt = 1
        clock = pygame.time.Clock()
        do_run = True
        self.prepare_particles(self.WIDTH / 2, self.HEIGHT / 2, self.HEIGHT // 3)
        while do_run:
            for event in pygame.event.get():
                if event.type == pygame.QUIT:
                    do_run = False
                    break
            self.screen.fill((0, 0, 0))
            self.particles.update(dt=dt)
            self.particles.draw(self.screen)

            pygame.display.flip()
            dt = clock.tick(60)

if "__main__" == __name__:
    pygame.init()
    pgm = PGMTest()
    pgm.prepare_window()
    pgm.run()
    pygame.quit()