Traceback (most recent call last):
      File "C:PythonPython36pygame projectsspace invaders.py", line 163, in <module>
        bullet.hideturtle()
      File "C:PythonPython36libturtle.py", line 2322, in hideturtle
        self.pen(shown=False)
      File "C:PythonPython36libturtle.py", line 2459, in pen
        self._update()
      File "C:PythonPython36libturtle.py", line 2660, in _update
        self._update_data()
      File "C:PythonPython36libturtle.py", line 2646, in _update_data
        self.screen._incrementudc()
      File "C:PythonPython36libturtle.py", line 1292, in _incrementudc
        raise Terminator
    turtle.Terminator

enemies = []
number_of_enemies = 5
for i in range(number_of_enemies):
    enemies.append(turtle.Turtle())

for enemy in enemies:
    enemy.color("green")
    enemy.shape("circle")
    enemy.penup()
    enemy.speed(0)
    x = random.randint(-200, 200)
    y = random.randint(100, 250)
    enemy.setposition(x, y)

enemyspeed = 2

def isCollision(t1, t2):
    distance = math.sqrt(math.pow(t1.xcor() - t2.xcor(), 2)+ math.pow(t1.ycor() - t2.ycor(), 2))
    if distance < 15:
        return True
    else:
        return False



while True:

for enemy in enemies:
    x = enemy.xcor()
    x += enemyspeed
    enemy.setx(x)

    if enemy.xcor() > 280:
        for e in enemies:
            y = enemy.ycor()
            y -= 40
            enemy.sety(y)
        enemyspeed *= -1

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

    if bulletstate == "fire":
        y = bullet.ycor()
        y += bulletspeed
        bullet.sety(y)

    if isCollision(bullet, enemy):
        #reset the bullet
        bullet.hideturtle()
        bulletstate = "ready"
        bullet.setposition(0, -400)
        #reset the enemy
        x = random.randint(-200, 200)
        y = random.randint(100, 250)
        enemy.setposition(x, y)

    if isCollision(player, enemy):
        player.hideturtle()
        enemy.hideturtle()
        print ("Get To The Doctors! You're Riddled!")
        break

from turtle import Turtle, Screen
from random import randint

NUMBER_OF_ENEMIES = 5
ENEMY_JUMP = 40

BULLET_SPEED = 20
PLAYER_SPEED = 15

SAFETY_DISTANCE = 15

GALLERY_WIDTH, GALLERY_HEIGHT = 560, 550
GALLERY_BORDER = 80

# player movement
def move_left():
    x = player.xcor() - PLAYER_SPEED

    if x < -GALLERY_WIDTH / 2:
        x = -GALLERY_WIDTH / 2

    player.setx(x)

def move_right():
    x = player.xcor() + PLAYER_SPEED

    if x > GALLERY_WIDTH / 2:
        x = GALLERY_WIDTH / 2

    player.setx(x)

def fire_bullet():
    global bulletstate

    if bulletstate == 'ready':
        bulletstate = 'fire'
        bullet.setposition(player.position())
        bullet.forward(BULLET_SPEED / 2)
        bullet.showturtle()

def isCollision(t1, t2):
    return t1.distance(t2) < SAFETY_DISTANCE

def move():
    global enemy_speed, bulletstate

    screen.tracer(False)

    for enemy in enemies:
        x = enemy.xcor() + enemy_speed

        enemy.setx(x)

        if x > GALLERY_WIDTH / 2:
            for e in enemies:
                y = e.ycor() - ENEMY_JUMP
                e.sety(y)

            enemy_speed *= -1

        elif x < -GALLERY_WIDTH / 2:
            for e in enemies:
                y = e.ycor() - ENEMY_JUMP
                e.sety(y)

            enemy_speed *= -1

        if isCollision(player, enemy):
            player.hideturtle()
            enemy.hideturtle()
            print("Get To The Doctors! You're Riddled!")
            screen.update()
            return

        if isCollision(bullet, enemy):
            # reset the bullet
            bullet.hideturtle()
            bullet.setposition(0, -GALLERY_HEIGHT)
            bulletstate = 'ready'

            # reset the enemy
            enemy.hideturtle()
            x = randint(GALLERY_BORDER - GALLERY_WIDTH / 2, GALLERY_WIDTH / 2 - GALLERY_BORDER)
            y = randint(GALLERY_HEIGHT / 2 - 175, GALLERY_HEIGHT / 2 - 25)
            enemy.setposition(x, y)
            enemy.showturtle()

    if bulletstate == 'fire':
        bullet.forward(BULLET_SPEED)

        # check to see if the bullets has gone to the top
        if bullet.ycor() > GALLERY_HEIGHT / 2:
            bullet.hideturtle()
            bulletstate = 'ready'

    screen.tracer(True)

    screen.ontimer(move, 25)

screen = Screen()
screen.setup(GALLERY_WIDTH + GALLERY_BORDER, GALLERY_HEIGHT + GALLERY_BORDER)
screen.bgcolor('black')

player = Turtle('turtle', visible=False)
player.speed('fastest')
player.color('red')
player.penup()
player.setheading(90)
player.sety(-250)  # need to define this
player.showturtle()

enemies = []

enemy_speed = 1

for _ in range(NUMBER_OF_ENEMIES):
    enemy = Turtle('circle', visible=False)
    enemy.speed('fastest')
    enemy.color('green')
    enemy.penup()

    x = randint(GALLERY_BORDER - GALLERY_WIDTH / 2, GALLERY_WIDTH / 2 - GALLERY_BORDER)
    y = randint(GALLERY_HEIGHT / 2 - 175, GALLERY_HEIGHT / 2 - 25)  # define these!
    enemy.setposition(x, y)
    enemy.showturtle()

    enemies.append(enemy)

# create the player's spunk shots
bullet = Turtle('triangle', visible=False)
bullet.speed('fastest')
bullet.shapesize(0.5)
bullet.color('white')
bullet.penup()
bullet.setheading(90)

# define bullet state
# ready - ready to fire
# fire - bullet is firing
bulletstate = 'ready'

screen.onkey(move_left, 'Left')
screen.onkey(move_right, 'Right')
screen.onkey(fire_bullet, 'space')

screen.listen()

move()

screen.mainloop()