为什么要赢得这项工作，为什么动画片会在定义中获胜

Question

我正在尝试让云从左到右动画并返回基本屏幕，当我不使用定义并将其放入游戏循环时，它会起作用，那为什么它会停止工作里面的定义？

import pygame, sys
from pygame.locals import *

pygame.init()

FPS = 30
fpsClock = pygame.time.Clock()

width = 500
length = 300
DISPLAYSURF = pygame.display.set_mode((width, length), 0, 32)
pygame.display.set_caption('Test')

def Clouds():
    BROWN = ( 139, 69, 19)
    GREEN = (  0, 255,   0)
    LIGHT_BLUE = ( 135, 206, 250)
    global cloudimg, cloudx, cloudy
    cloudimg = pygame.image.load('Cartoon_cloud.png')
    direction = 'left'
    cloudx = 100
    cloudy = 70

    DISPLAYSURF.fill(LIGHT_BLUE)
    pygame.draw.rect(DISPLAYSURF, BROWN, (0, 285, width, 15))
    pygame.draw.rect(DISPLAYSURF, GREEN, (0, 280, width, 5))

    if direction == 'left':
        cloudx += 1
        if cloudx == 450:
            direction = 'right'
    elif direction == 'right':
        cloudx -= 1
        if cloudx == 0:
            direction = 'left'

while True:
    Clouds()
    DISPLAYSURF.blit(cloudimg, (cloudx, cloudy))
    for event in pygame.event.get():
        if event.type == QUIT:
            pygame.quit()
            sys.exit()
    pygame.display.update()
    fpsClock.tick(FPS)