【python】An Introduction to Interactive Programming in Python(week two)

This is a note for https://class.coursera.org/interactivepython-005

In week two, I have learned:

1.event-drvien programing

4 event types:

Input: button, textbox

Keyborad: key up, key down

Mouse: click, drag

Timer

example:

# Example of a simple event-driven program

# CodeSkulptor GUI module
import simplegui

# Event handler
def tick():
    print "tick!"

# Register handler
timer = simplegui.create_timer(1000, tick)

# Start timer
timer.start()

2. global variables

when you want to change the global variables, use global, ifelse you don‘t need global.(不需更改全局变量，只是想使用全局变量的值的时候，不需要声明global)

3. simpleGUI

Program structure with 7 steps:

①Globals (state)

②Helper functions

③Classes

④Define event handlers

⑤Create a frame

⑥Register event handlers

⑦Start frame & timers

# SimpleGUI program template

# Import the module
import simplegui

# Define global variables (program state)
counter = 0
# Define "helper" functions
def increment():
    global counter
    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("SimpleGUI Test", 100, 100)
frame.add_button("Click me!", buttonpress)
# Register event handlers
timer = simplegui.create_timer(1000, tick)

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

Simple Calculator

Data

　　Store

　　Operand

Operations

　　print

　　Swap

　　Add

　　Subtract

　　Multiple

　　Divide

Computation

　　Store = store operation operand

# calculator with all buttons

import simplegui

# intialize globals
store = 0
operand = 0

# event handlers for calculator with a store and operand

def output():
    """prints contents of store and operand"""
    print "Store = ", store
    print "Operand = ", operand
    print ""

def swap():
    """ swap contents of store and operand"""
    global store, operand
    store, operand = operand, store
    output()

def add():
    """ add operand to store"""
    global store
    store = store + operand
    output()

def sub():
    """ subtract operand from store"""
    global store
    store = store - operand
    output()

def mult():
    """ multiply store by operand"""
    global store
    store = store * operand
    output()

def div():
    """ divide store by operand"""
    global store
    store = store / operand
    output()

def enter(t):
    """ enter a new operand"""
    global operand
    operand = int(t)
    output()

# create frame
f = simplegui.create_frame("Calculator",300,300)

# register event handlers and create control elements
f.add_button("Print", output, 100)
f.add_button("Swap", swap, 100)
f.add_button("Add", add, 100)
f.add_button("Sub", sub, 100)
f.add_button("Mult", mult, 100)
f.add_button("Div", div, 100)
f.add_input("Enter", enter, 100)

# get frame rolling
f.start()