User Interaction

Python Events

An “event” in Python is when something
happens that our app can react to.

Widget Events

Tkinter Widgets trigger different types of events
when a user interacts with the app.

Event Types

The most common types of events are:

• 
  Mouse Events
  click, move, hover
• 
  Keyboard Events
  key down, key up
• 
  Change Events
  resize, select, focus

Things We Need

To react to an event we need three things:

• A Widget
  
  Which widget will trigger the event?
• The Event Name
  
  Which event are we expecting?
• A Function
  
  What code do we want to run in response?

Event Binding

We use the bind function to link all the parts together:

import tkinter
window = tkinter.Tk()

def say_hello(event):
    print("Why hello there!")

mystery_button = tkinter.Button(window)
mystery_button.config(text="Click Me")
mystery_button.bind("<Button>", say_hello)
mystery_button.grid()

window.mainloop()

This is just an example - we’ll do a demo next!

Events Demo

Open up eventsdemo.py
so we can add some event handling to it.

Click Events

Add a click event binding to the hello_button:

hello_button = tkinter.Button(window)
hello_button.config(text="Click Me")
hello_button.bind("<Button>", say_hello)
hello_button.grid()

Clicking the button should print “Hello!” in the console.

More Click Events

Make the other buttons work, too:

• Add Random Fruit
• Delete Fruit
• Generate Recipe

Keyboard Events

Bind the name entry box to the <Return> event,
so that pressing “enter” does the same as clicking the button.

Challenge: Stuff To Do

Complete todo.py with events and functionality
so that it is a working To-Do app.