Walls

Lesson 26 of 41 in Coddy's Make Games with Pygame course.

The game ends when the head would leave the grid. A cell is on the grid when its column is from 0 to COLS - 1 and its row from 0 to ROWS - 1.

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:
        # insert, eat or pop, as before

Note x >= COLS, not x > COLS: columns are numbered from 0, so column COLS is already past the edge.

Test before you move. The head never goes off the grid, and once alive is false the snake stays where it was. Show Game over centred at (240, 180) while it is false.

Challenge

Medium

End the game when the snake hits a wall.

Set alive = True before the loop, and put the move under if alive:.
If the new cell (x, y) is off the grid, set alive = False; otherwise insert, eat or pop as before.
When alive is false, show Game over centred at (240, 180).

Press Play and hit a wall: Game over shows and the snake stops. 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

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

    x = body[0][0] + direction[0]
    y = body[0][1] + direction[1]
    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))
    pygame.display.flip()
    clock.tick(10)

pygame.quit()