Summary

• Python's slicing allows efficient extraction of subsequences from lists and tuples using the syntax list[start:end:step]
• Slicing works identically for both lists and tuples
• In practical applications like the snake game, slicing simplifies code by eliminating complex loops and conditional statements

Resources

Notes\ Code

We now have collision with the snakes tail causing a game over like hitting the walls, the food randomly spawns, the tail extends when the food is eaten and we have a scoreboard keeping count of the food eaten by the snake. Our snake game is pretty much done. Here is a look at the state of the code:

main.py

from turtle import Screen
from snake import Snake
from food import Food
from scoreboard import Scoreboard
import time

screen = Screen()
screen.setup(width=600, height=600)
screen.bgcolor("black")
screen.title("Snake Game")
screen.tracer(0)

score = Scoreboard()
snake = Snake()
food = Food()

screen.listen()
screen.onkey(snake.up,"Up")
screen.onkey(snake.down,"Down")
screen.onkey(snake.left, "Left")
screen.onkey(snake.right, "Right")

game_is_on = True

while game_is_on:
    screen.update()
    time.sleep(.1)
    snake.move()

    #Detect collision with food
    if snake.head.distance(food) < 15:
        food.refresh()
        snake.extend()
        score.increase_score()

    #Detect collision with wall
    if snake.head.xcor() > 280 or snake.head.xcor()< -280 or snake.head.ycor() > 280 or snake.head.ycor() < -280:
        game_is_on = False
        score.game_over()

    for segment in snake.segments:
        if segment == snake.head:
            pass
        elif snake.head.distance(segment) < 10:
            game_is_on = False
            score.game_over()

screen.exitonclick()

snake.py

from turtle import Turtle

STARTING_POSITIONS = [(0, 0), (-20, 0), (-40, 0)]
MOVE_DISTANCE = 20
UP = 90
DOWN = 270
LEFT = 180
RIGHT = 0

class Snake:
    def __init__(self):
        self.segments = []
        self.create_snake()
        self.head = self.segments[0]

    def create_snake(self):
        for position in STARTING_POSITIONS:
            self.add_segment(position)

    def add_segment(self, position):
        new_segment = Turtle("square")
        new_segment.color("white")
        new_segment.penup()
        new_segment.goto(position)
        self.segments.append(new_segment)

    def extend(self):
        self.add_segment(self.segments[-1].position())

    def move(self):
        for seg_num in range(len(self.segments) - 1, 0, -1):
            new_x = self.segments[seg_num - 1].xcor()
            new_y = self.segments[seg_num - 1].ycor()
            self.segments[seg_num].goto(new_x, new_y)
        self.segments[0].forward(MOVE_DISTANCE)

    def up(self):
        if self.head.heading() != DOWN:
            self.head.setheading(UP)

    def down(self):
        if self.head.heading() != UP:
            self.head.setheading(DOWN)

    def right(self):
        if self.head.heading() != LEFT:
            self.head.setheading(RIGHT)

    def left(self):
        if self.head.heading() != RIGHT:
            self.head.setheading(LEFT)

food.py

from turtle import Turtle
import random

class Food(Turtle):
    def __init__(self):
        super().__init__()
        self.shape("circle")
        self.penup()
        self.shapesize(stretch_len=0.5, stretch_wid=0.5)
        self.color("blue")
        self.speed("fastest")
        self.refresh()

    def refresh(self):
        random_x = random.randint(-260, 260)
        random_y = random.randint(-260, 260)
        self.goto(random_x, random_y)

scoreboard.py

from turtle import Turtle
ALIGNMENT = "center"
FONT = ("Arial", 12, "normal")

class Scoreboard(Turtle):
    def __init__(self):
        super().__init__()
        self.hideturtle()
        self.goto(0,280)
        self.color("white")
        self.score = 0
        self.update_scoreboard()

    def update_scoreboard(self):
        self.write(f"Score: {self.score}", align= ALIGNMENT, font=FONT)

    def game_over(self):
        self.penup()
        self.goto(0,0)
        self.write("GAME OVER", align=ALIGNMENT,  font=FONT)

    def increase_score(self):
        self.score += 1
        self.clear()
        self.update_scoreboard()

Now we want to rewrite the code for the section of main that checks if the head has collided with the tail. This:

    for segment in snake.segments:
        if segment == snake.head:
            pass
        elif snake.head.distance(segment) < 10:
            game_is_on = False
            score.game_over()

Its quite wordy and be better written with….