Don't Bite Yourself

Lesson 27 of 41 in Coddy's Make Games with Pygame course.

The game also ends when the head runs into the body. Add it to the test that ends the game:

if x < 0 or x >= COLS or y < 0 or y >= ROWS or (x, y) in body[:-1]:
    alive = False

The test uses body[:-1], every cell except the last. On a step without food, the tail moves out of its cell in the same step. Chasing your own tail is safe, so the tail cell does not count.

[:-1] is a slice: the list from the start up to, but not including, the last item.

Challenge

Hard

End the game when the snake bites itself.

Find the test that ends the game at the walls.
Also end it when the new head (x, y) is in body[:-1].

Press Play, eat a few times, then turn back into your body: Game over. Then Check.

Try it yourself

import random
import pygame

CELL = 20
COLS, ROWS = 24, 18
TURNS = {
    pygame.K_LEFT: (-1, 0),
    pygame.K_RIGHT: (1, 0),
    pygame.K_UP: (0, -1),
    pygame.K_DOWN: (0, 1),
}

pygame.init()
screen = pygame.display.set_mode((COLS * CELL, ROWS * CELL))
pygame.display.set_caption("Snake")
clock = pygame.time.Clock()
font = pygame.font.Font(None, 32)


def draw_cell(cell, color):
    col, row = cell
    pygame.draw.rect(screen, color, (col * CELL + 1, row * CELL + 1, CELL - 2, CELL - 2))


def new_food(body):
    while True:
        cell = (random.randrange(COLS), random.randrange(ROWS))
        if cell not in body:
            return cell


body = [(5, 9), (4, 9), (3, 9)]
direction = (1, 0)
food = new_food(body)
score = 0
alive = True

running = True
while running:
    moving = direction
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False
        elif event.type == pygame.KEYDOWN and event.key in TURNS:
            turn = TURNS[event.key]
            if turn != (-moving[0], -moving[1]):
                direction = turn

    if alive:
        x = body[0][0] + direction[0]
        y = body[0][1] + direction[1]
        if x < 0 or x >= COLS or y < 0 or y >= ROWS:
            alive = False
        else:
            body.insert(0, (x, y))
            if (x, y) == food:
                score += 1
                food = new_food(body)
            else:
                body.pop()

    screen.fill((30, 30, 46))
    draw_cell(food, (235, 80, 80))
    for cell in body[1:]:
        draw_cell(cell, (120, 220, 120))
    draw_cell(body[0], (180, 255, 160))
    score_text = font.render(f"Score: {score}", True, (240, 240, 240))
    screen.blit(score_text, (8, 6))
    if not alive:
        message = font.render("Game over", True, (240, 240, 240))
        screen.blit(message, message.get_rect(center=(240, 180)))
    pygame.display.flip()
    clock.tick(10)

pygame.quit()