code for tokyoed

import turtle
import os

wn = turtle.Screen()
wn.bgcolor("black")
wn.title("Space Invaders")

border_pen = turtle.Turtle()
border_pen.speed(0)
border_pen.color("white")
border_pen.penup()
border_pen.setposition(-300,-300)
border_pen.pensize(3)
for side in range(4):
    border_pen.fd(600)
    border_pen.lt(90)
    border_pen.hideturtle()

    player = turtle.Turtle()
    player.color("blue")
    player.shape("triangle")
    player.penup()
    player.speed(0)
    player.setposition(0, -250)
    player.setheading(90)

    playerspeed = 15

    def move_left():
        x = player.xcor()
        x -= playerspeed
        if x < -280:
            x = -280
        player.setx(x)

        def move_right():
            x = player.xcor()
            x += playerspeed
            if x > 280:
                x = 280
            player.setx(x)

        turtle.listen()
        turtle.onkey(move_left, "Left")
        turtle.onkey(move_right, "Right")