How do i get random enemies to appear from list

Im trying to get a random car to appear from a list of cars saved in variables. The issue seems to be it chooses a random car from the list and doesn't change it while the game is being played. Id like to change the car each time the previous car goes off screen.

Each time the game starts it chooses one car from the random list, but does not change the car each time the game loop runs.

I have pasted the code below:

import pygame
import time
import random

pygame.init()





display_width = 800
display_height = 600

black = (0, 0, 0)
white = (255, 255, 255)
red = (200, 0, 0)
green = (0, 200, 0)
bright_red = (255, 0, 0)
bright_green = (0, 255, 0)
block_color = (53, 115, 255)

crash_sound = pygame.mixer.Sound("crash.mp3")

car_width = 55

gameDisplay = pygame.display.set_mode((display_width, display_height))
pygame.display.set_caption('Super Racer')
clock = pygame.time.Clock()

gameIcon = pygame.image.load('carIcon.png')

backgroundImage = pygame.image.load("background.png")
backgroundImage = pygame.transform.scale(backgroundImage, (800, 600))
gameDisplay.blit(backgroundImage, (0, 0))

carImg = pygame.image.load("racecar.png")
carImg = pygame.transform.scale(carImg, (60, 100)) # resize graphic
carImg = carImg.convert_alpha() # remove whitespace from graphic

car1 = pygame.image.load("diablo.png")
car1 = pygame.transform.scale(car1, (60, 100)) # resize graphic
car1 = car1.convert_alpha() # remove whitespace from graphic

car2 = pygame.image.load("aventador.png")
car2 = pygame.transform.scale(car2, (60, 100)) # resize graphic
car2 = car2.convert_alpha() # remove whitespace from graphic

car3 = pygame.image.load("nsx.png")
car3 = pygame.transform.scale(car3, (60, 100)) # resize graphic
car3 = car3.convert_alpha() # remove whitespace from graphic

car4 = pygame.image.load("speeder.png")
car4 = pygame.transform.scale(car4, (60, 100)) # resize graphic
car4 = car4.convert_alpha() # remove whitespace from graphic

car5 = pygame.image.load("slr.png")
car5 = pygame.transform.scale(car5, (60, 100)) # resize graphic
car5 = car5.convert_alpha() # remove whitespace from graphic

car6 = pygame.image.load("Mach6.png")
car6 = pygame.transform.scale(car6, (60, 100)) # resize graphic
car6 = car6.convert_alpha() # remove whitespace from graphic

car7 = pygame.image.load("Stingray.png")
car7 = pygame.transform.scale(car7, (60, 100)) # resize graphic
car7 = car7.convert_alpha() # remove whitespace from graphic

car8 = pygame.image.load("bike.png")
car8 = pygame.transform.scale(car8, (60, 100)) # resize graphic
car8 = car8.convert_alpha() # remove whitespace from graphic

randomCars = [car1, car2, car3, car4, car5, car6, car7, car8]
enemy = random.choice(randomCars)

pygame.display.set_icon(gameIcon)

pause = False


# crash = True

def score(count):
    font = pygame.font.SysFont("comicsansms", 25)
    text = font.render("SCORE: " + str(count), True, red)
    gameDisplay.blit(text, (0, 0))


def things(thingx, thingy, thingw, thingh, color):
    #pygame.draw.rect(gameDisplay, color, [thingx, thingy, thingw, thingh])
    gameDisplay.blit(enemy, [thingx, thingy, thingw, thingh])

def car(x, y):
    gameDisplay.blit(carImg, (x, y))


def text_objects(text, font):
    textSurface = font.render(text, True, black)
    return textSurface, textSurface.get_rect()


def crash():
    ####################################
    pygame.mixer.Sound.play(crash_sound)
    pygame.mixer.music.stop()
    ####################################
    largeText = pygame.font.SysFont("comicsansms", 115)
    TextSurf, TextRect = text_objects("You Crashed", largeText)
    TextRect.center = ((display_width / 2), (display_height / 2))
    gameDisplay.blit(TextSurf, TextRect)

    while True:
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                pygame.quit()
                quit()

        button("Play Again", 150, 450, 100, 50, green, bright_green, game_loop)
        button("Quit", 550, 450, 100, 50, red, bright_red, quitgame)

        pygame.display.update()
        clock.tick(15)


def button(msg, x, y, w, h, ic, ac, action=None):
    mouse = pygame.mouse.get_pos()
    click = pygame.mouse.get_pressed()

    if x + w > mouse[0] > x and y + h > mouse[1] > y:
        pygame.draw.rect(gameDisplay, ac, (x, y, w, h))
        if click[0] == 1 and action != None:
            action()
    else:
        pygame.draw.rect(gameDisplay, ic, (x, y, w, h))
    smallText = pygame.font.SysFont("comicsansms", 20)
    textSurf, textRect = text_objects(msg, smallText)
    textRect.center = ((x + (w / 2)), (y + (h / 2)))
    gameDisplay.blit(textSurf, textRect)


def quitgame():
    pygame.quit()
    quit()


def unpause():
    global pause
    pygame.mixer.music.unpause()
    pause = False


def paused():
    ############
    pygame.mixer.music.pause()
    #############
    largeText = pygame.font.SysFont("comicsansms", 115)
    TextSurf, TextRect = text_objects("Paused", largeText)
    TextRect.center = ((display_width / 2), (display_height / 2))
    gameDisplay.blit(TextSurf, TextRect)

    while pause:
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                pygame.quit()
                quit()

        button("Continue", 150, 450, 100, 50, green, bright_green, unpause)
        button("Quit", 550, 450, 100, 50, red, bright_red, quitgame)

        pygame.display.update()
        clock.tick(15)


def game_intro():
    intro = True

    while intro:
        for event in pygame.event.get():
            # print(event)
            if event.type == pygame.QUIT:
                pygame.quit()
                quit()

        gameDisplay.fill(white)
        largeText = pygame.font.SysFont("comicsansms", 115)
        TextSurf, TextRect = text_objects("Super Racer", largeText)
        TextRect.center = ((display_width / 2), (display_height / 2))
        gameDisplay.blit(TextSurf, TextRect)

        button("LEGGO!", 150, 450, 100, 50, green, bright_green, game_loop)
        button("Quit", 550, 450, 100, 50, red, bright_red, quitgame)

        pygame.display.update()
        clock.tick(15)


def game_loop():
    global pause
    ############
    pygame.mixer.music.load('bgmusic.mp3')
    pygame.mixer.music.play(-1)
    ############
    x = (display_width * 0.45)
    y = (display_height * 0.8)

    x_change = 0

    thing_startx = random.randrange(0, display_width)
    thing_starty = -600
    enemy_speed = 4
    thing_width = 100
    thing_height = 100

    thingCount = 1

    dodged = 0

    gameExit = False

    while not gameExit:

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

            if event.type == pygame.KEYDOWN:
                if event.key == pygame.K_LEFT:
                    x_change = -5
                if event.key == pygame.K_RIGHT:
                    x_change = 5
                if event.key == pygame.K_p:
                    pause = True
                    paused()

            if event.type == pygame.KEYUP:
                if event.key == pygame.K_LEFT or event.key == pygame.K_RIGHT:
                    x_change = 0

        x += x_change

        gameDisplay.blit(backgroundImage, (0, 0))

        things(thing_startx, thing_starty, thing_width, thing_height, block_color)

        thing_starty += enemy_speed
        car(x, y)
        score(dodged)

        if x > display_width - car_width or x < 0:
            crash()

        if thing_starty > display_height:
            thing_starty = 0 - thing_height
            thing_startx = random.randrange(0, display_width)
            dodged += 1
            enemy_speed += .25


        if y < thing_starty + thing_height:
            #print('y crossover')

            if x > thing_startx and x < thing_startx + thing_width or x + car_width > thing_startx and x + car_width < thing_startx + thing_width:
                #print('x crossover')
                crash()

        pygame.display.update()
        clock.tick(60)


game_intro()
game_loop()
pygame.quit()
quit()