Space Invaders week 4

import turtle


#Screen Setup

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

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

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

turtlespeed = 15

#Create  the enemy
enemy = turtle.Turtle()
enemy.color("red")
enemy.shape("circle")
enemy.penup()
enemy.speed(0)
enemy.setposition(-200, 250)

enemyspeed = 2

#Create the player's bullet
bullet.turtle.Turtle()
bullet.color("yellow")
bullet.shape("triangle")
bullet.penup()
bullet.speed(0)
bullet.setheading(90)
bullet.shapesize(0.5, 0.5)
bullet.hideturtle()

bulletspeed = 20

#Define bullet state
#ready - to fire
#fire - bullet is firing
bulletstate = "ready"


#Move player left and right

def move_Left ():
    x = turtle.xcor()
    x -= turtlespeed
    if x < -280:
        x = - 280
    player.setx(x)

def move_Right():
    x = turtle.xcor()
    x += turtlespeed
    if x < -280:
        x = - 280
    player.setx(x)

def fire_bullet():
    #Declare bulletstate as a global if it needs changed
    global bulletstate

    #Move the bullet to just above player
    x = player.xcor()
    y = player.ycor() + 10
    bullet.setposition(x, y)
    bullet.showturtle()


#Create keyboard bindings
turtle.listen()
turtle.onkey(move_Left, "Left")
turtle.onkey(move_Right, "Right")
turtle.onkey(fire_bullet, "space")

#Main game loop
while True:

    #Move the enemy
    x = enemy.xcor()
    x += enemyspeed
    enemy.setx(x)

    #Move the enemy back and down
    if enemy.xcor() > 280:
        y = enemy.ycor()
        y  -= 40
        enemyspeed *= - 1
        enemy.sety(y)

    if enemy.xcor() < - 280:
        y = enemy.ycor()
        y  -= 40
        enemyspeed *= - 1
        enemy.sety(y)








wn.mainloop()