Vertical scrolling background image

# change the name of the filename

import pygame
import sys

width = 400
heigh = 400
FPS = 60

screen = pygame.display.set_mode((width,heigh))
pygame.display.set_caption('Space Invaders: Closing Up')
clock = pygame.time.Clock()

class Background():
    def __init__(self):
        self.image = pygame.image.load('background.jpg').convert() # change the nam
        self.w, self.h = self.image.get_rect().size
        self.y = 0

    def update(self, display):
        self.y += 1
        if self.y > self.h:
            self.y = 0

        display.blit(self.image, (0, self.y))
        display.blit(self.image, (0, self.y - self.h))

bg = Background()
while True:
    for event in pygame.event.get():
        if event.type == pygame.QUIT or (event.type == pygame.KEYDOWN and event.key == pygame.K_ESCAPE):
            pygame.quit()
            sys.exit()

    bg.update(screen)

    pygame.display.update()
    clock.tick(FPS)