Python GUI Program

Program Structure:
    Globals (state)
    Helper Functions
    Classes (later)
    Define event handler
    Create a frame
    Register event handler
    Start frame & timers

Example:

# SimpleGUI program template

# Import the module
import simplegui

# Define global variables (program state)
counter = 0

# Define "helper" functions
def increment():
    global counter
    counter += 1
    
# Define event handler functions
def tick():
    increment()
    print counter

def buttonpress():
    global counter
    counter = 0

# Create a frame
frame = simplegui.create_frame("Simple GUI test", 100, 100)

# Register event handlers
timer = simplegui.create_timer(1000, tick)
frame.add_button("Click me!", buttonpress)

# Start frame and timers
frame.start()
timer.start()

Canvas (Drawing on GUI):

# first example of drawing on the canvas

import simplegui

# define draw handler
def draw(canvas):
    canvas.draw_text("Hello!",[100, 100], 24, "White")
    canvas.draw_circle([100, 100], 2, 2, "Red")

# create frame
frame = simplegui.create_frame("Text drawing", 300, 200)

# register draw handler    
frame.set_draw_handler(draw)

# start frame
frame.start()

Interactive Drawing

# interactive application to convert a float in dollars and cents

import simplegui

# define global value

value = 3.12

# Handle single quantity
def convert_units(val, name):
    result = str(val) + " " + name
    if val > 1:
        result = result + "s"
    return result
        
# convert xx.yy to xx dollars and yy cents
def convert(val):
    # Split into dollars and cents
    dollars = int(val)
    cents = int(round(100 * (val - dollars)))

    # Convert to strings
    dollars_string = convert_units(dollars, "dollar")
    cents_string = convert_units(cents, "cent")

    # return composite string
    if dollars == 0 and cents == 0:
        return "Broke!"
    elif dollars == 0:
        return cents_string
    elif cents == 0:
        return dollars_string
    else:
        return dollars_string + " and " + cents_string
    

# define draw handler
def draw(canvas):
    canvas.draw_text(convert(value), [60, 110], 24, "White")


# define an input field handler
def input_handler(text):
    global value
    value = float(text)


# create frame
frame = simplegui.create_frame("Converter", 400, 200)

# register event handlers
frame.set_draw_handler(draw)
frame.add_input("Enter value", input_handler, 100)


# start frame
frame.start()

Timer. Timer update for specified time interval. Draw update 60Hz.

# Simple "screensaver" program.

# Import modules
import simplegui
import random

# Global state
message = "Python is Fun!"
position = [50, 50]
width = 500
height = 500
interval = 2000

# Handler for text box
def update(text):
    global message
    message = text
    
# Handler for timer
def tick():
    x = random.randrange(0, width)
    y = random.randrange(0, height)
    position[0] = x
    position[1] = y

# Handler to draw on canvas
def draw(canvas):
    canvas.draw_text(message, position, 36, "Red")

# Create a frame 
frame = simplegui.create_frame("Home", width, height)

# Register event handlers
text = frame.add_input("Message:", update, 150)
frame.set_draw_handler(draw)
timer = simplegui.create_timer(interval, tick)

# Start the frame animation
frame.start()
timer.start()