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O'Reilly Book Excerpts: Python Programming on Win32

Python Programming on Win32 using Tkinter

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Python Programming On Win32
Help for Windows Programmers
By Mark Hammond, Andy Robinson

by Mark Hammond

An excerpt from Chapter 20: GUI Development, from Python Programming on Win32. This is the first of three excerpts covering Tkinter, PythonWin, and wxPython. This excerpt only covers Tkinter.

In this chapter, we examine the various options for developing graphical user interfaces (GUIs) in Python.

We will look in some detail at three of the GUI toolkits that operate on the Windows platform: Tkinter, PythonWin, and wxPython. Each of these GUI toolkits provide a huge range of facilities for creating user interfaces, and to completely cover any of these toolkits is beyond the scope of this single chapter. Each framework would need its own book to do it justice.

Our intent in this chapter is to give you a feel for each of these GUI frameworks, so you can understand the basic model they use and the problems they were designed to address. We take a brief tour of each of these toolkits, describing their particular model and providing sample code along the way. Armed with this information, you can make an informed decision about which toolkit to use in which situation, have a basic understanding of how your application will look, and where it will run when finished.

The authors need to express their gratitude to Gary Herron for the Tkinter section, and Robin Dunn for the wxPython section. Their information helped us complete this chapter.

Tkinter

Tkinter is the Python interface to the Tk GUI toolkit current maintained by Scriptics (http://www.scriptics.com). Tkinter has become the de facto standard GUI toolkit for Python due mainly to its cross-platform capabilities; it presents a powerful and adaptable GUI model across the major Python platforms, including Windows 95/98/NT, the Macintosh, and most Unix implementations and Linux distributions.

This section gives a short description of the capabilities of Tkinter, and provides a whirlwind tour of the more important aspects of the Tkinter framework. To effectively use Tkinter, you need a more thorough description than is provided for here. Fredrik Lundh has made an excellent introduction to Tkinter programming available at http://www.pythonware.com/library.htm, and at time of printing a Tkinter book by Fredrik has just been announced, so may be available by the time you read this. For more advanced uses of Tkinter, you may need to refer directly to the Tk reference manual, available from the Scriptics site.

Two Python applications, tkBrowser and tkDemo, accompany this section. TkBrowser is a Doubletalk application, providing several views and some small editing capabilities of Doubletalk BookSets; TkDemo demonstrates a simple use of the core Tk user interface elements. Both applications are too large to include in their entirety, so where relevant, we include snippets.

Terminology

There's some new terminology with Tkinter, defined here for clarity:

Tk
A GUI toolkit provided as a library of C routines. This library manages and manipulates the windows and handles the GUI events and user interaction.

Tkinter
The Python Tk interface. A Python module that provides a collection of Python classes and methods for accessing the Tk toolkit from within Python.

Tcl
The (mostly hidden) language used by Tk and, hence, used by Tkinter to communicate with the Tk toolkit.

Widget
A user interface element, such as a text box, combo box, or top-level window. On Windows, the common terminology is control or window.

Pros and Cons of Tkinter

Before we launch into Tkinter programming, a brief discussion of the pros and cons of Tkinter will help you decide if Tkinter may be the correct GUI toolkit for your application. The following are often given as advantages of Tkinter:

Brevity
Python programs using Tkinter can be very brief, partly because of the power of Python, but also due to Tk. In particular, reasonable default values are defined for many options used in creating a widget, and packing it (i.e., placing and displaying).

Cross platform
Tk provides widgets on Windows, Macs, and most Unix implementations with very little platform-specific dependence. Some newer GUI frameworks are achieving a degree of platform independence, but it will be some time before they match Tk's in this respect.

Maturity
First released in 1990, the core is well developed and stable.

Extensibility
Many extensions of Tk exist, and more are being frequently distributed on the Web. Any extension is immediately accessible from Tkinter, if not through an extension to Tkinter, than at least through Tkinter's access to the Tcl language.

To balance things, here's a list of what's often mention as weaknesses in Tkinter:

Speed
There is some concern with the speed of Tkinter. Most calls to Tkinter are formatted as a Tcl command (a string) and interpreted by Tcl from where the actual Tk calls are made. This theoretical slowdown caused by the successive execution of two interpreted languages is rarely seen in practice and most real-world applications spend little time communicating between the various levels of Python, Tcl, and Tk.

Tcl
Python purists often balk at the need to install another (and to some, a rival) scripting language in order to perform GUI tasks. Consequently, there is periodic interest in removing the need for Tcl by using Tk's C-language API directly, although no such attempt has ever succeeded.

Tk lacks modern widgets
It's acknowledged that Tk presents a small basic set of widgets and lacks a collection of modern fancy widgets. For instance, Tk lacks paned windows, tabbed windows, progress meter widgets, and tree hierarchy widgets. However, the power and flexibility of Tk is such that you can easily construct new widgets from a collection of basic widgets. This fits in especially well with the object-oriented nature of Python.

Native look and feel
One common source of complaints is that Tkinter applications on Windows don't look like native Windows applications. As we shall see, the current version of Tkinter provides an interface that should be acceptable to almost everyone except the Microsoft marketing department, and we can expect later versions of Tkinter to be virtually indistinguishable.

Although many individuals could (and no doubt will) argue with some individual points on this list, it tends to reflects the general consensus amongst the Python community. Use this only as a guide to assist you in your decision-making process.

 

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