使用Pygame从列表随机生成自定义类对象的耗尽问题

使用Python 3.10.4和Pygame开发游戏时，在主循环中尝试用random.choice从列表生成自定义类对象流遇到问题：代码能运行，但列表中的每个对象仅被生成一次后就不再重复生成。

相关代码片段：

def run_game(self):
    """Start the main loop for the game."""
    list_of_particles = [Particle__SO2(self),Particle__H20(self),Particle__CO2(self),Particle__H2S(self), Particle__CO2(self)]
    while True:
        self._check_events()
        self.clock.tick(25)
        new_particle = random.choice(list_of_particles)
        self.particles.add(new_particle)
        self._update_particles()

完整代码：

import sys
import pygame
from pygame.sprite import Sprite
import random

class Volcano_game:
    """Overall class to manage game assets and behavior."""

    def __init__(self):
        """Initialize the game, and create game resources."""
        pygame.init()
        self.screen = pygame.display.set_mode((1920, 1080))
        self.particles = pygame.sprite.Group()
        self.vent_location_xy = (952, 881)
        self.io_surface_y = 950
        self.gravity = 1
        self.clock = pygame.time.Clock()
        self.alpha_surf = pygame.Surface(self.screen.get_size(), pygame.SRCALPHA)

    def run_game(self):
        """Start the main loop for the game."""
        list_of_particles = [Particle__SO2(self),Particle__H20(self),Particle__CO2(self),Particle__H2S(self), Particle__CO2(self)]
        while True:
            self._check_events()
            self.clock.tick(25)
            new_particle = random.choice(list_of_particles)
            self.particles.add(new_particle)
            self._update_particles()
            

            self.update_screen()
            
            self.alpha_surf.fill((255, 255, 255, 250),
                                special_flags=pygame.BLEND_RGBA_MULT)

    def _update_particles(self):
        """Update position of particles and get rid of old particles."""
        # Update bullet positions.
        self.particles.update()

        # Get rid of particles that have landed or gone off screen.
        for particle in self.particles.copy():
            if particle.y > self.io_surface_y:
                self.particles.remove(particle)
            elif particle.y < 0:
                self.particles.remove(particle)
            elif particle.x < 0:
                self.particles.romove(particle)  # 存在拼写错误
            elif particle.x > 1920:
                self.particles.remove(particle)

    def update_screen(self):
        """Update images on the screen, and flip to the new screen."""
        self.screen.fill((0, 0, 0))
        
        
        self.screen.blit(self.alpha_surf, (0, 0))
        for particle in self.particles.sprites():
            particle.draw_particle()

        pygame.display.flip()

    def _check_events(self):
        """Respond to keypresses and mouse events."""
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                sys.exit()

class Particle(Sprite):
    """a class to manage sprites fired from the volcano"""

    def __init__(self, vg_game):
        super().__init__()
        self.screen = vg_game.alpha_surf
        self.colour = (60, 255, 60)

        self.rect_x = 952
        self.rect_y = 881
        self.y = self.rect_y
        self.x = self.rect_x
        self.speed_y = -15
        self.speed_x = (random.randint(-11, 11))
        self.gravity = vg_game.gravity

    def update(self):
        """move the particle around the screen"""
        # update the decimal position of the particle
        self.y += self.speed_y
        self.x += self.speed_x
        self.speed_y += self.gravity
        self.rect_y = self.y
        self.rect_x = self.x

    def draw_particle(self):
        """draw the particle on the screen"""
        pygame.draw.circle(self.screen, self.colour,
                            (self.rect_x, self.rect_y), 2)


class Particle__SO2(Particle):

    def __init__(self, vg_game):
        super().__init__(vg_game)
        self.colour = (255, 255, 255)

        self.speed_y = -17


class Particle__H20(Particle):
    def __init__(self, vg_game):
        super().__init__(vg_game)
        self.colour = (0, 0, 255)

        self.speed_y = -52.5


class Particle__CO2(Particle):
    def __init__(self, vg_game):
        super().__init__(vg_game)
        self.colour = (255, 0, 0)

        self.speed_y = -24.72

class Particle__H2S(Particle):
    def __init__(self, vg_game):
        super().__init__(vg_game)
        self.colour = (255, 255, 0)

        self.speed_y = -31.9

if __name__ == '__main__':
    # Make a game instance, and run the game.
    vg = Volcano_game()
    vg.run_game()

你在list_of_particles里存放的是已经实例化完成的粒子对象，而不是粒子类本身。每次调用random.choice时，只是从列表里选出同一个对象实例，把它添加到sprite组中。当这个实例被_update_particles方法移除后，再次添加它也不会生成新的粒子——因为它还是原来那个对象，状态已经是移出屏幕的状态了。

把列表改成存储粒子类，而不是实例。每次随机选择后，调用类并传入self来创建新的粒子实例：

修改run_game方法：

def run_game(self):
    """Start the main loop for the game."""
    # 存储类，而不是实例
    list_of_particles = [Particle__SO2, Particle__H20, Particle__CO2, Particle__H2S, Particle__CO2]
    while True:
        self._check_events()
        self.clock.tick(25)
        # 随机选择类，然后创建新实例
        particle_class = random.choice(list_of_particles)
        new_particle = particle_class(self)
        self.particles.add(new_particle)
        self._update_particles()
        
        self.update_screen()
        
        self.alpha_surf.fill((255, 255, 255, 250),
                            special_flags=pygame.BLEND_RGBA_MULT)

另外，注意修复_update_particles方法中的拼写错误：把self.particles.romove(particle)改成self.particles.remove(particle)，否则当粒子超出左边界时会报错。

内容的提问来源于stack exchange，提问作者Mike B