Our application needs to monitor, or listen for, all the events that we find interesting, and respond to them in some way if they occur. Some events could also be triggered by occurrences which are not controlled by the user - for example, a background task might complete, or a network connection might be established or lost. We say that an event is fired whenever the user does something - for example, clicks on a button or types a keyboard shortcut.

Anything that happens in a user interface is an event. GUIs often use a form of OO programming which we call event-driven : the program responds to eventswhich are actions that a user takes. We will see how to make a simple GUI which handles user input and output. If you learn the basics of tkinteryou should see many similarities should you try to use a different toolkit. There are many other toolkits available, but they often vary across platforms.

In this chapter we will use tkintera module in the Python standard library which serves as an interface to Tk, a simple toolkit.

Now we will briefly look at creating a program with a graphical user interfaceor GUI. We have previously seen how to write text-only programs which have a command-line interfaceor CLI.

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