How to write a snake game with python and pygame (2020 tutorial)

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# snake game
import pygame, sys, random
from pygame.locals import *

SCREEN_WIDTH = 640
SCREEN_HEIGHT = 480

FPS = 5
TILE_SIZE = 20

# color set up
BLACK = (0,0,0)
WHITE = (255,255,255)
GREEN = (0,255,0)
RED = (255,0,0)


def draw_grid():
      # draw 25 horizontal lines
      for i in range(25):
            pygame.draw.line(screen, WHITE, (0,i * TILE_SIZE), (639,i * TILE_SIZE))
            
      # draw  33 vertical lines
      for j in range(33):
            pygame.draw.line(screen, WHITE, (j * TILE_SIZE,0), (j * TILE_SIZE, 479))

def draw_snake(snake_list):
      
      for pos in snake_list:
            x, y = pos
            rect = pygame.Rect(x*TILE_SIZE,y*TILE_SIZE,TILE_SIZE, TILE_SIZE)
            pygame.draw.rect(screen, GREEN, rect)

def moving_snake(direction):
      global snake_list
      if direction == 'E':
            for i in range(len(snake_list)-1, 0, -1):
                  snake_list[i] = snake_list[i-1].copy()
            snake_list[0][0] += 1
      elif direction == 'W':
            for i in range(len(snake_list)-1, 0, -1):
                  snake_list[i] = snake_list[i-1].copy()
            snake_list[0][0] += -1
      elif direction == 'N':
            for i in range(len(snake_list)-1, 0, -1):
                  snake_list[i] = snake_list[i-1].copy()
            snake_list[0][1] += -1
      elif direction == 'S':
            for i in range(len(snake_list)-1, 0, -1):
                  snake_list[i] = snake_list[i-1].copy()
            snake_list[0][1] += 1

      draw_snake(snake_list)

def generate_apple(random_pos):
      global screen
      apple_rect = pygame.Rect(random_pos[0]*TILE_SIZE,random_pos[1]*TILE_SIZE,TILE_SIZE, TILE_SIZE)
      pygame.draw.rect(screen, RED, apple_rect)

def get_random_pos_for_apple():
      global snake_list
      random_pos = [random.randint(0,31), random.randint(0,23)]
      while random_pos in snake_list:
            random_pos = [random.randint(0,31), random.randint(0,23)]
      return random_pos

def elongate_snake(moving_dir):
      global snake_list
      if moving_dir == 'N':
            new_head = [snake_list[0][0], snake_list[0][1]-1]
            snake_list.insert(0, new_head)
      elif moving_dir == 'S':
            new_head = [snake_list[0][0], snake_list[0][1]+1]
            snake_list.insert(0, new_head)
      elif moving_dir == 'E':
            new_head = [snake_list[0][0]+1, snake_list[0][1]]
            snake_list.insert(0, new_head)
      else:
            new_head = [snake_list[0][0]-1, snake_list[0][1]]
            snake_list.insert(0, new_head)

def collide_with_border(snake_list):
      return not (0 <= snake_list[0][0] <= 31 and 0 <= snake_list[0][1] <= 23)

def collide_with_body(snake_list):
      if snake_list[0] in snake_list[1:]:
            return True
      else:
            return False

def show_game_over_text():
      global screen
      text_font = pygame.font.SysFont('arial', 50)
      game_over_surf = text_font.render('Game Over!', True, WHITE)
      screen.blit(game_over_surf, (180, 150))
      
pygame.init()
screen = pygame.display.set_mode((SCREEN_WIDTH, SCREEN_HEIGHT))
pygame.display.set_caption('snake')

# snake head start position (15,11)
snake_head = pygame.Rect(15*TILE_SIZE,11*TILE_SIZE,TILE_SIZE, TILE_SIZE)

# create a snake list to contain its head and body coordinates
# at first, there is only the default head position
snake_list = [[15,11]]

# moving direction of the snake, east by default 'E'
moving_dir = 'E'

game_clock = pygame.time.Clock()

apple_eaten = True

game_over = False

while True:
      # print(snake_list)
      for event in pygame.event.get():
            if event.type == QUIT:
                  pygame.quit()
                  sys.exit()
            elif event.type == KEYDOWN:
                  if event.key == K_UP and moving_dir != 'S':
                        moving_dir = 'N'
                  elif event.key == K_DOWN and moving_dir != 'N':
                        moving_dir = 'S'
                  elif event.key == K_LEFT and moving_dir != 'E':
                        moving_dir = 'W'
                  elif event.key == K_RIGHT and moving_dir != 'W':
                        moving_dir = 'E'
            
            
      screen.fill(BLACK)
      draw_grid()
      if apple_eaten:
            apple_pos = get_random_pos_for_apple()
            apple_eaten = False
      generate_apple(apple_pos)
      
      moving_snake(moving_dir)
      if snake_list[0] == apple_pos: # if snake ate apple
            apple_eaten = True
            elongate_snake(moving_dir)

      if collide_with_border(snake_list):# head go out of borders
            show_game_over_text()
            game_over = True

      if collide_with_body(snake_list):
            show_game_over_text()
            game_over = True
      
      pygame.display.update()
      
      if game_over:
            break
      game_clock.tick(FPS)

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