This is snake game we all play when we were child's.

food.py

from turtle import Turtle
import random


class Food(Turtle):

    def __init__(self):
        super().__init__()
        self.shape("circle")
        self.penup()
        self.shapesize(0.5, 0.5)
        self.color("blue")
        self.speed("fastest")
        self.refresh()

    def refresh(self):
        random_x = random.randint(-280, 280)
        random_y = random.randint(-280, 280)
        self.goto(random_x, random_y)

main.py

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


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

snake = Snake()
food = Food()
scoreboard = Score()
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(0.1)
    snake.move()

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

    # Detect collision with tail.

    for segment in snake.segments[1:]:
        if snake.head.distance(segment) < 10:
            scoreboard.reset()
            snake.reset()


screen.exitonclick()

scoreboar.py

from turtle import Turtle

ALIGNMENT = "center"
FONT = ("Courier", 24, "normal")


class Score(Turtle):
    def __init__(self):
        super().__init__()
        with open("data.txt") as data:
            self.high_score = int(data.read())
        self.score = 0
        self.color("white")
        self.penup()
        self.goto(0, 260)
        self.hideturtle()
        self.update_scoreboard()

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

    def reset(self):
        if self.score > self.high_score:
            self.high_score = self.score
            with open("data.txt", mode="w") as data:
                data.write(f"{self.high_score}")
        self.score = 0
        self.update_scoreboard()

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

snake.py

from turtle import Turtle

STARTING_POSITION = [(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_POSITION:
            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 reset(self):
        for seg in self.segments:
            seg.goto(1000, 1000)
        self.segments.clear()
        self.create_snake()
        self.head = self.segments[0]

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

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