Parallax python

import pygame
import os, sys

def main():
    pygame.init()

    ecran = pygame.display.set_mode((1200, 600))
    pygame.display.set_caption('Le rêve de Robotnik')

    jeu_en_cours = True

    while jeu_en_cours :

        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                jeu_en_cours = FALSE

            if event.type == pygame.KEYDOWN:
                if event.key == pygame.K_ESCAPE:
                    jeu_en_cours = False

        image1 = load_image('background_fix.png', ecran)
        ecran.blit(image1, (0, 0))
        image2 = load_image('background_middle.png', ecran)
        ecran.blit(image2, (0, 0))
        image3 = load_image('background_front.png', ecran)
        ecran.blit(image3, (0, 0))
        pygame.display.flip()

    pygame.quit()

def load_image(name, ecran, colorkey=None):
    fullname = os.path.join('resources/', name)
    image = pygame.image.load(fullname)
    return image

def parallaxe(window, image, position_x, speed):
    window = ecran
    image1 = load_image('background_fix.png', ecran)
    image2 = load_image('background_middle.png', ecran)
    image3 = load_image('background_front.png', ecran)
    position_x = 0
    speed = 10


    screen    

if __name__ == "__main__":
    main()