asteroids | Python Fiddle

import time
import turtle
import math
import random

time_before   = 0

window_width  = 600
window_height = 600
window_left   = -(window_width  / 2)
window_right  =   window_width  / 2
window_bottom = -(window_height / 2)
window_top    =   window_height / 2
# 7 numbers: x,y, vx,vy, angle, turn_rate, size
ship  = [0] * 7

# INDEX NAMES:
# These variables give names to the indexes in the above list
X     = 0
Y     = X + 1
VX    = Y + 1
VY    = VX + 1
ANGLE = VY + 1
RATE  = ANGLE + 1
SIZE  = RATE + 1

# This list will hold all the rock motion records
rocks = []

# And this list will hold the bullet motion records
bullets = []

# Notice how the index names make the code more readable
def move_object(motion, T):
    motion[X]     += motion[VX] * T
    motion[Y]     += motion[VY] * T
    motion[ANGLE] += motion[RATE] * T

def wrap_around(motion):
    if   motion[X] > window_right:
         motion[X] = window_left
    elif motion[X] < window_left:
         motion[X] = window_right
    elif motion[Y] > window_top:
         motion[Y] = window_bottom
    elif motion[Y] < window_bottom:
         motion[Y] = window_top

def move_rocks(T):
    for rock in rocks:
        wrap_around(rock)
        move_object(rock, T)

def draw_rock(motion_record):
    x     = motion_record[X]
    y     = motion_record[Y]
    angle = motion_record[ANGLE]
    size  = motion_record[SIZE]
    turtle.penup()
    turtle.goto(x, y)
    turtle.setheading(angle)
    turtle.forward(size)
    turtle.pendown()
    turtle.left(60)
    for side in range(6):
        turtle.left(60)
        turtle.forward(size)

def draw_rocks():
    for rock in rocks:
        draw_rock(rock)
    
def draw_bullet(bullet):
    turtle.penup()
    turtle.goto(bullet[X], bullet[Y])
    turtle.dot(bullet[SIZE])

def draw_objects():
    turtle.tracer(False)
    turtle.hideturtle()
    turtle.clear()

draw_rocks()
    draw_bullets()
    turtle.tracer(True)
    
def collided(motion1, motion2):
    x1 = motion1[X]
    y1 = motion1[Y]
    radius1 = motion1[SIZE]

x2 = motion2[X]
    y2 = motion2[Y]
    radius2 = motion2[SIZE]

dx = x1 - x2
    dy = y1 - y2
    distance = math.sqrt(dx * dx  +  dy * dy)
    if distance < (radius1 + radius2):
        return True
    else:
        return False

def move_objects(T):
    move_rocks(T)
    move_bullets(T)
    remove_offscreen_bullets()

def update_scene():
    global time_before
    time_now = time.time()
    time_elapsed = time_now - time_before

move_objects(time_elapsed)
    check_rock_bullet_hit()
    draw_objects()

time_before = time_now
    turtle.ontimer(update_scene, 100)

#######################################################################
# THE FUNCTIONS YOU MUST MODIFY ARE BELOW THIS LINE
#
# |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
# v   v   v   v   v   v   v   v   v   v   v   v   v   v   v   v   v   v

def random_motion():
    x = random.randrange(window_left, window_right)
    y = random.randrange(window_bottom, window_top)
    vx = random.random() * 200 - 100
    vy = random.random() * 200 - 100
    rotation_rate = random.random() * 200 - 100
    return [x, y, vx, vy, 0, rotation_rate, 20]

def make_rocks():
    global rocks
    rocks.append(random_motion())

def move_bullets(T):
    return

def remove_offscreen_bullets():
    return

def fire_bullet():
    global bullets

angle      = ship[ANGLE]
    gun_offset = ship[SIZE]
    speed      = 40  # 40 pixels per second
    bullet = [0] * 7
    
    # (ux uy) is a unit vector pointing in the ship's direction
    ux = math.cos(math.radians(angle))
    uy = math.sin(math.radians(angle))

bullet[X] = ship[X] + gun_offset * ux
    bullet[Y] = ship[Y] + gun_offset * uy
    bullet[VX] = ux * speed
    bullet[VY] = uy * speed
    bullet[SIZE] = 5

bullets.append(bullet)

def draw_bullets():
    return

def check_rock_bullet_hit():
    return

def turn_ship_left():
    return

def turn_ship_right():
    return
    
def main():
    global time_before
    
    turtle.setup(window_width, window_height, 0,0)
    turtle.Screen()

turtle.onkey(fire_bullet, ' ')

turtle.ontimer(update_scene, 100)
    time_before = time.time()

make_rocks()
    
    turtle.listen()
    turtle.mainloop()

# ^   ^   ^   ^   ^   ^   ^   ^   ^   ^   ^   ^   ^   ^   ^   ^   ^   ^
# |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
#
# THE FUNCTIONS YOU MUST MODIFY ARE ABOVE THIS LINE
#######################################################################

if __name__ == '__main__':
    main()

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