Pygame Sprite

import pygame
 
WIDTH=800
HEIGHT=650
FPS=30
 
WHITE=(255,255,255)
BLACK=(0,0,0)
RED=(250,0,0)
GREEN=(0,255,0)
BLUE=(0,0,255)
 
class Player(pygame.sprite.Sprite):
    def __init__(self):
          pygame.sprite.Sprite.__init__(self)
          self.image=pygame.Surface((50,50))
          self.image.fill(GREEN)
          self.rect=self.image.get_rect()
          self.rect.center=(400,325)
 
    def update(self):
        if self.rect.left < WIDTH:
            self.rect.x += 5
        if self.rect.right > WIDTH:
            self.rect.left = 0
            self.rect.x -= 5
            
 
pygame.init()
screen=pygame.display.set_mode((WIDTH, HEIGHT))
pygame.display.set_caption("My Game")
clock=pygame.time.Clock()
 
all_sprites=pygame.sprite.Group()
player=Player()
all_sprites.add(player)
 
running=True
while running:
    clock.tick(FPS)
    for event in pygame.event.get():
        if event.type==pygame.QUIT:
            running=False
 
    all_sprites.update()
    screen.fill(BLACK)
    all_sprites.draw(screen)
    pygame.display.flip()  
pygame.quit()

speed = 5
 
def update(self):
    if self.rect.right >= WIDTH or self.rect.left<=0:
        speed *= -1
        
    self.rect.x += speed