simple parallax scroll in pygame

parallax.py

import sys
import pygame
import math
from pygame.locals import *

TILE_SIZE = 16
HORIZONTAL_TILES = 20
VERTICAL_TILES = 10
SCREEN_WIDTH = TILE_SIZE * HORIZONTAL_TILES
SCREEN_HEIGHT = TILE_SIZE * VERTICAL_TILES

BLACK = Color(0, 0, 0)

def getTile(tileset, tileX, tileY):
	r = Rect(tileX * TILE_SIZE, tileY * TILE_SIZE, TILE_SIZE, TILE_SIZE)
	return tileset.subsurface(r)

def createLayers(tileset):
	layer1tile = getTile(tileset, 5, 1)
	layer2tile = getTile(tileset, 5, 0)
	layer3tile = getTile(tileset, 5, 2)
	backgroundTile = getTile(tileset, 7, 3)

	layer1 = pygame.Surface((SCREEN_WIDTH, TILE_SIZE), 0, screen)
	layer2 = pygame.Surface((SCREEN_WIDTH, TILE_SIZE), 0, screen)
	layer3 = pygame.Surface((SCREEN_WIDTH, TILE_SIZE), 0, screen)
	background = pygame.Surface((SCREEN_WIDTH, TILE_SIZE), 0, screen)

	for i in range(HORIZONTAL_TILES):
		layer1.blit(layer1tile, (i * TILE_SIZE, 0))
		layer2.blit(layer2tile, (i * TILE_SIZE, 0))
		layer3.blit(layer3tile, (i * TILE_SIZE, 0))
		background.blit(backgroundTile, (i * TILE_SIZE, 0))

	return layer1, layer2, layer3, background


def handleEvents():
	for event in pygame.event.get():
		if event.type == pygame.QUIT:
			sys.exit()
		if event.type == pygame.KEYDOWN and event.key == K_q:
			sys.exit()

pygame.init()
screen = pygame.display.set_mode([SCREEN_WIDTH, SCREEN_HEIGHT])

# 128x224 px for ca 8x12 tiles
tileset = pygame.image.load("OverworldTileset_v03.png").convert()
layers = createLayers(tileset)
layer1surface, layer2surface, layer3surface, backgroundSurface = layers
layer1offset = 0
layer2offset = 0
layer3offset = 0
backgroundOffset = 0

while True:
	# events
	handleEvents()

	# logic

	layer1offset = (layer1offset - 4) % SCREEN_WIDTH
	layer2offset = (layer2offset - 3) % SCREEN_WIDTH
	layer3offset = (layer3offset - 2) % SCREEN_WIDTH
	backgroundOffset = (backgroundOffset - 1) % SCREEN_WIDTH

	# render

	screen.blit(layer1surface, (layer1offset, 5 * TILE_SIZE))
	screen.blit(layer1surface, (layer1offset - SCREEN_WIDTH, 5 * TILE_SIZE))

	screen.blit(layer2surface, (layer2offset, 4 * TILE_SIZE))
	screen.blit(layer2surface, (layer2offset - SCREEN_WIDTH, 4 * TILE_SIZE))

	screen.blit(layer3surface, (layer3offset, 3 * TILE_SIZE))
	screen.blit(layer3surface, (layer3offset - SCREEN_WIDTH, 3 * TILE_SIZE))

	screen.blit(backgroundSurface, (backgroundOffset, 2 * TILE_SIZE))
	screen.blit(backgroundSurface, (backgroundOffset - SCREEN_WIDTH, 2 * TILE_SIZE))

	pygame.display.flip()
	pygame.time.wait(10)

depends on the image OverworldTileset_v03.png. It is not that important. Just replace it with your own image and change the dimensions