Python - Keyboard input in GUI

# Keyboard echo

import simplegui

# initialize state
current_key = ' '

# event handlers
def keydown(key):
    global current_key
    current_key = chr(key)
    
def keyup(key):
    global current_key
    current_key = ' '
    
def draw(c):
    # NOTE draw_text now throws an error on some non-printable characters
    # Since keydown event key codes do not all map directly to
    # the printable character via ord(), this example now restricts
    # keys to alphanumerics
    
    if current_key in "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789":
        c.draw_text(current_key, [10, 25], 20, "Red")    
        
# create frame             
f = simplegui.create_frame("Echo", 35, 35)

# register event handlers
f.set_keydown_handler(keydown)
f.set_keyup_handler(keyup)
f.set_draw_handler(draw)

# start frame
f.start()

import simplegui

# Initialize globals
WIDTH = 600
HEIGHT = 400
BALL_RADIUS = 20

ball_pos = [WIDTH / 2, HEIGHT / 2]

# define event handlers
def draw(canvas):
    canvas.draw_circle(ball_pos, BALL_RADIUS, 2, "Red", "White")

def keydown(key):
    vel = 4
    if key == simplegui.KEY_MAP["left"]:
        ball_pos[0] -= vel
    elif key == simplegui.KEY_MAP["right"]:
        ball_pos[0] += vel
    elif key == simplegui.KEY_MAP["down"]:
        ball_pos[1] += vel
    elif key == simplegui.KEY_MAP["up"]:
        ball_pos[1] -= vel        
    
# create frame 
frame = simplegui.create_frame("Positional ball control", WIDTH, HEIGHT)

# register event handlers
frame.set_draw_handler(draw)
frame.set_keydown_handler(keydown)

# start frame
frame.start()