Snake Game In Python

Hey this is simple code for developing a snake game in Python:

Snake.py:

import random, pygame, sys, random
from pygame.locals import *
FPS = 10
WINDOWWIDTH = 640
WINDOWHEIGHT = 480
CELLSIZE = 20
assert WINDOWWIDTH % CELLSIZE == 0, "Window width must be a multiple of cell size."
assert WINDOWHEIGHT % CELLSIZE == 0, "Window height must be a multiple of cell size."
CELLWIDTH = int(WINDOWWIDTH / CELLSIZE)
CELLHEIGHT = int(WINDOWHEIGHT / CELLSIZE)
WHITE=(255,255,255)
RED=(255,0,0)
BLACK=(0,0,0)
GREEN=(0,255,0)
DARKGREEN=(0,155,0)
DARKGRAY=(40,40,40)
UP = 'up'
DOWN = 'down'
LEFT = 'left'
RIGHT = 'right'
HEAD = 0 
def main():
    global FPSCLOCK, DISPLAYSURF, BASICFONT, BACK
    pygame.mixer.pre_init(44100,16,2,4096)
    pygame.init()
    #pygame.display.set_icon("snake.jpg")
    pygame.display.set_caption('My Snake Game')
    FPSCLOCK=pygame.time.Clock()
    DISPLAYSURF=pygame.display.set_mode((WINDOWWIDTH, WINDOWHEIGHT))
    BACK=pygame.image.load('title.png')
    BACK=pygame.transform.scale(BACK,(WINDOWWIDTH,WINDOWHEIGHT))
    DISPLAYSURF.blit(BACK,(0,0))
    BASICFONT=pygame.font.Font('freesansbold.ttf', 18)
    backsound=pygame.mixer.Sound("backsong.wav")
    channel=backsound.play(-1)
    showStartScreen()
    while True:
        runGame()
        showGameOverScreen()
def runGame():
    # Set a random start point.
    pos=1
    startx = random.randint(5, CELLWIDTH - 6)
    starty = random.randint(5, CELLHEIGHT - 6)
    wormCoords = [{'x': startx,     'y': starty},
                  {'x': startx - 1, 'y': starty},
                  {'x': startx - 2, 'y': starty}]
    direction = RIGHT
    # Start the apple in a random place.
    apple = getRandomLocation()

    while True: 
        for event in pygame.event.get(): 
            if event.type == QUIT:
                terminate()
            elif event.type == KEYDOWN:
                if (event.key == K_LEFT or event.key == K_a) and direction!= RIGHT:
                    direction = LEFT
                elif (event.key == K_RIGHT or event.key == K_d) and direction != LEFT:
                    direction = RIGHT
                elif (event.key == K_UP or event.key == K_w) and direction!= DOWN:
                    direction = UP
                elif (event.key == K_DOWN or event.key == K_s) and direction != UP:
                    direction = DOWN
                elif event.key == K_ESCAPE:
                    terminate()

        if wormCoords[HEAD]['x'] == -1 or wormCoords[HEAD]['x'] == CELLWIDTH or wormCoords[HEAD]['y'] == -1 or wormCoords[HEAD]['y'] == CELLHEIGHT:
            return 
        for wormBody in wormCoords[1:]:
            if wormBody['x'] == wormCoords[HEAD]['x'] and wormBody['y'] ==wormCoords[HEAD]['y']:
                 return
        if wormCoords[HEAD]['x'] == apple['x'] and wormCoords[HEAD]['y']== apple['y']:
            apple = getRandomLocation() 
            hit=pygame.mixer.Sound("coin.ogg")
            hit=hit.play()
            pos=random.randint(1,7)
        else:
            del wormCoords[-1] 
        if direction == UP:
            newHead = {'x': wormCoords[HEAD]['x'], 'y':wormCoords[HEAD]['y'] - 1}
        elif direction == DOWN:
            newHead = {'x': wormCoords[HEAD]['x'], 'y':wormCoords[HEAD]['y'] + 1}
        elif direction == LEFT:
            newHead = {'x': wormCoords[HEAD]['x'] - 1, 'y':wormCoords[HEAD]['y']}
        elif direction == RIGHT:
            newHead = {'x': wormCoords[HEAD]['x'] + 1, 'y':wormCoords[HEAD]['y']}
        wormCoords.insert(0, newHead)
        BACK=pygame.image.load('gameback5.jpg')
        BACK=pygame.transform.scale(BACK,(WINDOWWIDTH,WINDOWHEIGHT))
        DISPLAYSURF.blit(BACK,(0,0))
        drawWorm(wormCoords)
        drawApple(apple,pos)
        drawScore(len(wormCoords) - 3)
        pygame.display.update()
        FPSCLOCK.tick(FPS)

def drawPressKeyMsg():
    pressKeySurf = BASICFONT.render('Press a key to play.', True, RED)
    pressKeyRect = pressKeySurf.get_rect()
    pressKeyRect.topleft = (WINDOWWIDTH - 400,30)
    DISPLAYSURF.blit(pressKeySurf, pressKeyRect)

def checkForKeyPress():
    if len(pygame.event.get(QUIT)) > 0:
        terminate()
    keyUpEvents = pygame.event.get(KEYUP)
    if len(keyUpEvents) == 0:
        return None
    if keyUpEvents[0].key == K_ESCAPE:
        terminate()
    return keyUpEvents[0].key

def showStartScreen():
    while True:
        drawPressKeyMsg()
        if checkForKeyPress():
            pygame.event.get()
            return
        pygame.display.update()

def terminate():
    pygame.quit()
    sys.exit()

def getRandomLocation():
    return {'x': random.randint(0, CELLWIDTH - 1), 'y': random.randint(0, CELLHEIGHT - 1)}

def showGameOverScreen():
    gameOverFont = pygame.font.Font('freesansbold.ttf', 150)
    gameSurf = gameOverFont.render('Game', True, WHITE)
    overSurf = gameOverFont.render('Over', True, WHITE)
    gameRect = gameSurf.get_rect()
    overRect = overSurf.get_rect()
    BACK=pygame.image.load('gameback4.jpg')
    BACK=pygame.transform.scale(BACK,(WINDOWWIDTH,WINDOWHEIGHT))
    DISPLAYSURF.blit(BACK,(0,0))
    gameRect.midtop = (WINDOWWIDTH / 2, 100)
    overRect.midtop = (WINDOWWIDTH / 2, gameRect.height + 100 + 25)
    DISPLAYSURF.blit(gameSurf, gameRect)
    DISPLAYSURF.blit(overSurf, overRect)
    drawPressKeyMsg()
    pygame.display.update()
    pygame.time.wait(500)
    checkForKeyPress()
    while True:
        if checkForKeyPress():
            pygame.event.get()
            
            return

def drawScore(score):
    scoreSurf = BASICFONT.render('Score: %s' % (score), True, WHITE)
    scoreRect = scoreSurf.get_rect()
    scoreRect.topleft = (WINDOWWIDTH - 120, 10)
    DISPLAYSURF.blit(scoreSurf, scoreRect)

def drawWorm(wormCoords):
    for coord in wormCoords:
        x = coord['x'] * CELLSIZE
        y = coord['y'] * CELLSIZE
        wormSegmentRect = pygame.Rect(x, y, CELLSIZE, CELLSIZE)
        pygame.draw.rect(DISPLAYSURF, DARKGREEN, wormSegmentRect)
        wormInnerSegmentRect = pygame.Rect(x + 4, y + 4, CELLSIZE - 8, CELLSIZE - 8)
        pygame.draw.rect(DISPLAYSURF, GREEN, wormInnerSegmentRect)

def drawApple(coord,pos):
    x = coord['x'] * CELLSIZE
    y = coord['y'] * CELLSIZE
    apple=pygame.image.load('apple%d.png'%pos)
    apple=pygame.transform.scale(apple,(CELLSIZE, CELLSIZE))
    DISPLAYSURF.blit(apple,(x,y))
if __name__== '__main__':
    main()

Have Funs.....................