Pygame Snake, Pt. 4

Source: Dev.to

Introduction

In Parts 1, 2, & 3 we assembled everything except the actual game logic. Now we’ll add the snake mechanics.

Replace the single dot with a snake list

Change the original definition:

dot = pygame.Vector2(W / 2, H / 2)

to:

snake = [pygame.Vector2(W / 2, H / 2)]

Add a growth counter

Just above the while loop, introduce:

grow = 3

This starts the snake with a length of 4.

Update the game loop

Compute the new head position

Replace dot += vel with:

new_head = snake[-1] + vel

Detect self‑collision

if new_head in snake:
    print("hit self")
    break

Append the new head

snake.append(new_head)

Handle growth vs. normal movement

if grow > 0:
    grow -= 1
else:
    snake.pop(0)

Draw the whole snake

Find the two lines that previously drew the single dot:

square = pygame.Rect(dot * S, (S, S))
screen.fill("black", square)

Replace them with a loop that draws every segment:

for dot in snake:
    square = pygame.Rect(dot * S, (S, S))
    screen.fill("black", square)

Full code at this point

import pygame
import random

W = 30
H = 30
S = 20

# pygame setup
pygame.init()
screen = pygame.display.set_mode((W * S, H * S))
clock = pygame.time.Clock()
running = True

# game setup
snake = [pygame.Vector2(W / 2, H / 2)]
vel = pygame.Vector2(1, 0)

key_vel = {
    pygame.K_RIGHT: pygame.Vector2(1, 0),
    pygame.K_DOWN: pygame.Vector2(0, 1),
    pygame.K_LEFT: pygame.Vector2(-1, 0),
    pygame.K_UP: pygame.Vector2(0, -1)
}

grow = 3

def place_food():
    global food_pos
    food_pos = pygame.Vector2(
        random.randrange(W),
        random.randrange(H)
    )
    while food_pos in snake:
        food_pos = pygame.Vector2(
            random.randrange(W),
            random.randrange(H)
        )

place_food()

while running:
    # poll for events
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False
        if event.type == pygame.KEYDOWN and event.key in key_vel:
            vel = key_vel[event.key]

    # clear screen
    screen.fill("white")

    new_head = snake[-1] + vel

    if new_head in snake:
        print("hit self")
        break

    if new_head == food_pos:
        grow += 1
        place_food()

    snake.append(new_head)

    if grow > 0:
        grow -= 1
    else:
        snake.pop(0)

    for dot in snake:
        square = pygame.Rect(dot * S, (S, S))
        screen.fill("black", square)

    square = pygame.Rect(food_pos * S, (S, S))
    screen.fill("green", square)

    # update display
    pygame.display.flip()

    # limit FPS
    clock.tick(20)

pygame.quit()

Next steps

Continue with the next part of the tutorial: Part 5.