GUI Programming with Tkinter
In this topic we look at how a GUI program is assembled in a general sense, then how this is done using Python's native GUI toolkit, Tkinter. This will not be a full blown Tkinter refence nor even a complete tutorial. There is already a very good and detailed tutor linked from the Python web site. This tutorial will instead try to lead you through the basics of GUI programming, introducing some of the basic GUI components and how to use them. We will also look at how Object Oriented programming can help organise a GUI application.
GUI principles
The first thing I want to say is that you won't learn anything new about programming here. Programming a GUI is exactly like any other kind of programming, you can use sequences, loops, branches and modules just as before. What is different is that in programming a GUI you usually use a Toolkit and must follow the pattern of program design laid down by the toolkit vendor. Each new toolkit will have its own API and set of design rules and you as a programmer need to learn these. This is why most programmers try to standardise on only a few toolkits which are available across multiple languages - learning a new toolkit tends to be much harder than learning a new programming language!
We are going to look at the Tk toolkit which is used in Tcl, Perl and Python. The principles in Tk are slightly different to other toolkits so I will conclude with a very brief look at another popular GUI toolkit for Python(and C/C++) which is more conventional in its approach. But first some general principles:
As we have already stated several times GUI applications are nearly always event driven by nature. If you don't remember what that means go back and look at the event driven programming topic.
I will assume that you are already familiar with GUIs as a user and will focus on how GUI programs work from a programmers perspective. I will not be going into details of how to write large complex GUIS with multiple windows, MDI interfaces etc. I will stick to the basics of creating a single window application with some labels, buttons, text boxes and message boxes.
First things first, we need to check our vocabulary. GUI programming has its own set of programming terms. The most common terms are described in the table below:
Term |
|
Description |
Window
Control
An area of the screen controlled by an application. Windows are usually rectangular but some GUI environments permit other shapes. Windows can contain other windows and frequently every single GUI control is treated as a window in its own right.
A control is a GUI object used for controlling the application. Controls have properties and usually generate events. Normally controls correspond to application level objects and the events are coupled to methods of the corresponding object such that when an event occurs the object executes one of its methods. The GUI environment usually provides a mechanism for binding events to methods.
Widget A control, sometimes restricted to visible controls. Some controls(such as timers) can be associated with a given window but are not visible. Widgets are that subset of controls which are visible and can be maniplulated by the user or programmer. The widgets that we shall cover are:
•Frame
•Label
•Button
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