text: # control the velocity of a ball using the arrow keys
  
  try:
      import simplegui
  except ImportError:
      import SimpleGUICS2Pygame.simpleguics2pygame as simplegui
  
  # Initialize globals
  WIDTH = 600
  HEIGHT = 400
  BALL_RADIUS = 20
  
  ball_pos = [WIDTH / 2, HEIGHT / 2]
  vel = [0, 0]
  
  # define event handlers
  def draw(canvas):
      # Update ball position
      ball_pos[0] += vel[0]
      ball_pos[1] += vel[1]
  
      # Draw ball
      canvas.draw_circle(ball_pos, BALL_RADIUS, 2, "Red", "White")
  
  def keydown(key):
      acc = 1
      if key==simplegui.KEY_MAP["left"]:
          vel[0] -= acc
      elif key==simplegui.KEY_MAP["right"]:
          vel[0] += acc
      elif key==simplegui.KEY_MAP["down"]:
          vel[1] += acc
      elif key==simplegui.KEY_MAP["up"]:
          vel[1] -= acc
  
      print ball_pos
  
  # create frame
  frame = simplegui.create_frame("Velocity ball control", WIDTH, HEIGHT)
  
  # register event handlers
  frame.set_draw_handler(draw)
  frame.set_keydown_handler(keydown)
  
  # start frame
  frame.start()
  
  