Python - PyGame - Snake

import pygame
import random

#
# pygame (simple) template by furas
#

# === CONSTANTS === UPPER_CASE names

DISPLAY_WIDTH = 800
DISPLAY_HEIGHT = 600

FPS = 5

BLACK = (  0,   0,   0)
WHITE = (255, 255, 255)

RED   = (255,   0,   0)
GREEN = (  0, 255,   0)
BLUE  = (  0,   0, 255)

BLOCK_SIZE = 50

# === CLASSES === CamelCase names

class Snake(): # now it is almost Snake(pygame.sprite.Sprite):

    def __init__(self, screen, x, y, tail_color=GREEN, head_color=BLUE):

        self.screen = screen
        self.screen_rect = screen.get_rect()

        # single tile position and size
        self.rect = pygame.Rect(x, y, BLOCK_SIZE, BLOCK_SIZE)

        # add one tile at start - `self.make_longer` will add more tiles
        self.tiles = [self.rect]

        # add automatically new 5 tiles (one tile in every step)
        self.make_longer = 5

        # you can use image file like PNG
        self.image_head = pygame.Surface( (BLOCK_SIZE, BLOCK_SIZE) )
        self.image_head.fill(head_color)

        self.image_tail = pygame.Surface( (BLOCK_SIZE, BLOCK_SIZE) )
        self.image_tail.fill(tail_color)

        # speed
        self.x_change = 0
        self.y_change = 0


    def draw(self):
        # draw all tiles without head ([1:])
        for tile_rect in self.tiles[1:]:
            self.screen.blit(self.image_tail, tile_rect)

        # draw head ([0])
        self.screen.blit(self.image_head, self.tiles[0])


    def update(self):
        # create new head
        self.head_rect = self.tiles[0].move(self.x_change, self.y_change)

        # wall colision - is head still on screen ?
        if not self.screen_rect.contains(self.head_rect):
            return False # dead

        # add head at beginning of tiles (now snake is longer)
        self.tiles.insert(0, self.head_rect)

        # make snake longer
        if not self.make_longer:
            # remove last tile to keep the same width
            del self.tiles[-1]
        else:
            # make longer (one tile in every step)
            self.make_longer -= 1

        return True # still alive


    def add(self):
        # add one tile to self.tiles
        self.make_longer = 1


class Food(): # now it is almost Food(pygame.sprite.Sprite):

    def __init__(self, screen):
        self.screen = screen

        # apple position and size
        self.rect = pygame.Rect(0, 0, BLOCK_SIZE, BLOCK_SIZE)
        self.spawn() # set random position

        # you can use image from file like PNG
        self.image = pygame.Surface( (BLOCK_SIZE, BLOCK_SIZE) )
        self.image.fill(RED)

    def spawn(self):
        self.rect.x = random.randrange(0, 800, BLOCK_SIZE)
        self.rect.y = random.randrange(0, 600, BLOCK_SIZE)

    def draw(self):
        self.screen.blit(self.image, self.rect)

# === FUNCTIONS === lower_case names


def main():

    score = 0

    # --- init ---

    pygame.init()

    game_display = pygame.display.set_mode((DISPLAY_WIDTH, DISPLAY_HEIGHT))
    game_display_rect = game_display.get_rect()

    pygame.display.set_caption('Snake')

    # --- objects ---

    schlange = Snake(game_display, game_display_rect.centerx, game_display_rect.centery, GREEN)
    essen = Food(game_display)

    # --- (constants) texts ---

    font = pygame.font.SysFont(None, 50)

    text_pause = font.render('PAUSE', True, WHITE)
    text_pause_rect = text_pause.get_rect()
    # center on screen
    text_pause_rect.center = game_display_rect.center

    text_game_over = font.render('GAME OVER', True, WHITE)
    text_game_over_rect = text_game_over.get_rect()
    # center on screen
    text_game_over_rect.center = game_display_rect.center

    # --- (changing) texts ---

    text_score = font.render('SCORE: '+ str(score), True, WHITE)
    text_score_rect = text_game_over.get_rect()
    # left top cornert
    text_score_rect.left = game_display_rect.left
    text_score_rect.top = game_display_rect.top

    # --- mainloop ---

    paused = False
    alive = True

    clock = pygame.time.Clock()
    running = True

    while running:

        # --- envents ---

        for event in pygame.event.get():

            # --- global events ---

            if event.type == pygame.QUIT:
                running = False

            # --- player events ---

            # you can move it into Snake.event_handle(event)
            # and call schlange.event_handle(event)

            if event.type == pygame.KEYDOWN:

                if event.key == pygame.K_UP:
                    if schlange.y_change == 0: # don't move backword
                        schlange.x_change = 0
                        schlange.y_change = -50

                elif event.key == pygame.K_DOWN:
                    if schlange.y_change == 0: # don't move backword
                        schlange.x_change = 0
                        schlange.y_change = 50

                elif event.key == pygame.K_LEFT:
                    if schlange.x_change == 0: # don't move backword
                        schlange.x_change = -50
                        schlange.y_change = 0

                elif event.key == pygame.K_RIGHT:
                    if schlange.x_change == 0: # don't move backword
                        schlange.x_change = 50
                        schlange.y_change = 0

                elif event.key == pygame.K_SPACE:
                    # pause/unpause game
                    paused = not paused

        # --- updates (without draws) ---

        if not paused and alive:
            # move snake
            alive = schlange.update()

            if alive:
                # check snake head collision with apple
                if schlange.tiles[0].colliderect(essen.rect):
                    # move apple to new position
                    essen.spawn()
                    # make snake longer
                    schlange.add()

                    # new score and new text
                    score += 1

                    text_score = font.render('SCORE: '+ str(score), True, WHITE)
                    text_score_rect = text_game_over.get_rect()
                    # left top cornert
                    text_score_rect.left = game_display_rect.left
                    text_score_rect.top = game_display_rect.top

        # --- all draws (without updates) ---


        # background
        game_display.fill(BLACK)

        # objects
        schlange.draw()
        essen.draw()

        # text and decorations

        game_display.blit(text_score, text_score_rect)

        if paused:
            game_display.blit(text_pause, text_pause_rect)

        if not alive:
            game_display.blit(text_game_over, text_game_over_rect)

        # move on screen
        clock.tick(FPS)
        pygame.display.update()

    # --- the end ---

    # quit or create ending screen
    pygame.quit()

# ---------------------------------------------------------------------

if __name__ == '__main__':
    main()