如何基于Python pygame实现动画跑马灯

import pygame
from random import randint, choice

screen_length = 700
screen_width = 500
# 模拟彩带飘落的类，掉落的词作为彩带
class Word_drop(pygame.sprite.Sprite):

  # 设置属性：包括字体、下落速度、彩带来源、彩带框的属性
  def __init__(self):
    pygame.sprite.Sprite.__init__(self)
    self.font = pygame.font.SysFont(name='幼圆', size=10, bold=True, italic=True)
    self.speed = randint(15, 30)
    self.word = self.getWord()
    self.image = self.font.render(self.word, True,
                   (randint(0, 255), randint(0, 255), randint(0, 255)))
    self.image = pygame.transform.rotate(self.image, randint(87, 93))
    self.rect = self.image.get_rect()
    self.rect.topleft = (randint(0, screen_length), -20)

  # 获取掉落的词
  def getWord(self):
    length = randint(1, 8)
    word = ''
    for i in range(length):
      word += choice('qwertyuiopasdfghjklzxcvbnm1234567890QWERTYUIOPASDFGHJKLZXCVBNM')
    return word

  # 设置彩带更新的条件
  def update(self, *args):
    self.rect = self.rect.move(0, self.speed)
    if self.rect.top > screen_length:
      self.kill()

# 实现"跑马灯"效果的函数
def word_translate(jx, ztw1, ztw2, screen_length, text):
  max_ztw = max(ztw1, ztw2)
  jx.x -= 5
  if jx.x < 0 - max_ztw:
    jx.x = (screen_length + 10)
  screen.blit(text, [jx.x, jx.y])

if __name__ == '__main__':

  # 初始化工作
  pygame.init()
  pygame.font.init()

  # 渲染字体，两行字
  a = pygame.font.SysFont(name='幼圆', size=50, bold=True, italic=True)

  word1 = "  中国"
  text1 = a.render(word1, True, (255, 0, 0), (0, 0, 0))

  word2 = "我超级爱你"
  text2 = a.render(word2, True, (255, 0, 0), (0, 0, 0))

  # "跑马场"字体框的属性
  _, _, ztw1, zth1 = text1.get_rect()
  jx1 = pygame.Rect(screen_length, (screen_width / 2 - zth1), ztw1, zth1)

  _, _, ztw2, zth2 = text2.get_rect()
  jx2 = pygame.Rect(screen_length, (screen_width / 2), ztw2, zth2)

  # 其他相关设置
  screen = pygame.display.set_mode((screen_length, screen_width))
  clock = pygame.time.Clock()
  wordGroup = pygame.sprite.Group()

  while True:

    clock.tick(30)
    screen.fill((0, 0, 0))

    # 设置退出的条件
    for event in pygame.event.get():
      if event.type == pygame.QUIT:
        pygame.quit()
        exit(0)

    # 彩带飘落
    word_object = Word_drop()
    wordGroup.add(word_object)
    wordGroup.update()
    wordGroup.draw(screen)

    # "跑马场"
    word_translate(jx1, ztw1, ztw2, screen_length, text1)
    word_translate(jx2, ztw1, ztw2, screen_length, text2)

    pygame.display.update()