How add audio to python game?

Question

So I have this python Snake game which I thought I was done with. But now I realized I want some background music as well (I have an mp3 in mind).

I've never worked with audiofiles like this but from what I have read and seen I should use pygame.mixer? I just have now idea how to implement it now that that I'm already starting to loose track of what I've written..

To take it one step further, I'd like there to be a little 'ding!' sound when the snake eats an apple, and a 'crash!' when it is running in to itself or a border.

I've experimented a lot with the pygame.mixer and looking at other peoples code and so on but whatever I do I get syntaxErrors.

To sum up:

1. How does one implement an audiofile in a python game, that should loop for as long as the game does and pause as soon as it is Game Over? Where, specifically, do I add this in my code?
2. What audio formats are acceptable? I've seen others with mp3, but would midi work as well for example?

Code below:

import random
import pygame
import sys
from pygame.locals import *

FPS = 9
WINDOWWIDTH = 928
WINDOWHEIGHT = 696
CELLSIZE = 29
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)

BLACK       = (0,   0,   0, )
WHITE       = (255, 255, 255)
YELLOW      = (254, 238, 184)
LIGHTYELLOW = (255, 250, 232)
RED         = (255, 120, 130)
DARKRED     = (232,  88,  99)
GREEN       = (148, 212, 138)
DARKGREEN   = (139, 201, 131)

BGCOLOR = YELLOW

UP = 'up'
DOWN = 'down'
LEFT = 'left'
RIGHT = 'right'

HEAD = 0

def main():
    global FPSCLOCK, DISPLAYSURF, BASICFONT

    pygame.init()
    FPSCLOCK = pygame.time.Clock()
    DISPLAYSURF = pygame.display.set_mode((WINDOWWIDTH, WINDOWHEIGHT))
    BASICFONT = pygame.font.Font('freesansbold.ttf', 28)
    pygame.display.set_caption('Snake!')

    showStartScreen()
    while True:
        runGame()
        showGameOverScreen()


def runGame():
    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

    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()
        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)
        DISPLAYSURF.fill(BGCOLOR)
        drawGrid()
        drawWorm(wormCoords)
        drawApple(apple)
        drawScore(len(wormCoords) - 3)
        pygame.display.update()
        FPSCLOCK.tick(FPS)

def drawPressKeyMsg():
    pressKeySurf = BASICFONT.render('Press a key to play.', True, BLACK)
    pressKeyRect = pressKeySurf.get_rect()
    pressKeyRect.topleft = (WINDOWWIDTH - 280, WINDOWHEIGHT - 42)
    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():
    titleFont = pygame.font.Font('freesansbold.ttf', 100)
    titleSurf1 = titleFont.render('Snake!', True, LIGHTYELLOW, GREEN)
    titleSurf2 = titleFont.render('Snake!', True, DARKGREEN)

    degrees1 = 0
    degrees2 = 0
    while True:
        DISPLAYSURF.fill(BGCOLOR)
        rotatedSurf1 = pygame.transform.rotate(titleSurf1, degrees1)
        rotatedRect1 = rotatedSurf1.get_rect()
        rotatedRect1.center = (WINDOWWIDTH / 2, WINDOWHEIGHT / 2)
        DISPLAYSURF.blit(rotatedSurf1, rotatedRect1)

        rotatedSurf2 = pygame.transform.rotate(titleSurf2, degrees2)
        rotatedRect2 = rotatedSurf2.get_rect()
        rotatedRect2.center = (WINDOWWIDTH / 2, WINDOWHEIGHT / 2)
        DISPLAYSURF.blit(rotatedSurf2, rotatedRect2)

        drawPressKeyMsg()

        if checkForKeyPress():
            pygame.event.get()
            return
        pygame.display.update()
        FPSCLOCK.tick(FPS)
        degrees1 += 3
        degrees2 += 7


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', 115)
    gameSurf = gameOverFont.render('Game', True, BLACK)
    overSurf = gameOverFont.render('Over!', True, BLACK)
    gameRect = gameSurf.get_rect()
    overRect = overSurf.get_rect()
    gameRect.midtop = (WINDOWWIDTH / 2, 60)
    overRect.midtop = (WINDOWWIDTH / 2, gameRect.height + 10 + 55)

    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, BLACK)
    scoreRect = scoreSurf.get_rect()
    scoreRect.topleft = (WINDOWWIDTH - 160, 18)
    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):
    x = coord['x'] * CELLSIZE
    y = coord['y'] * CELLSIZE
    appleSegmentRect = pygame.Rect(x, y, CELLSIZE, CELLSIZE)
    pygame.draw.rect(DISPLAYSURF, DARKRED, appleSegmentRect)
    appleInnerSegmentRect = pygame.Rect(x + 4, y + 4, CELLSIZE - 8, CELLSIZE - 8)
    pygame.draw.rect(DISPLAYSURF, RED, appleInnerSegmentRect)


def drawGrid():
    for x in range(0, WINDOWWIDTH, CELLSIZE):
        pygame.draw.line(DISPLAYSURF, LIGHTYELLOW, (x, 0), (x, WINDOWHEIGHT))
    for y in range(0, WINDOWHEIGHT, CELLSIZE):
        pygame.draw.line(DISPLAYSURF, LIGHTYELLOW, (0, y), (WINDOWWIDTH, y))


if __name__ == '__main__':
    main() 

Thank you in advance!

Johanna