Building a Better Mouse Trap

This chapter continues our look at building graphical user interfaces with Python and its standard Tkinter library by presenting a collection of realistic GUI programs. In the previous three chapters, we met all the basics of Tkinter programming and toured the core set of widgets -- Python classes that generate devices on a computer screen and may reply to user-generated events like mouseclicks. Here, our focus is on putting those widgets together to create more useful GUIs. We'll study:

• Advanced GUI coding techniques
• PyEdit -- a text editor program
• PyView -- an image slideshow
• PyDraw -- a painting program
• PyClock -- a graphical clock
• PyToe -- and even a simple game just for fun[1]

  [1] All of the larger examples in this book have a "Py" at the start of their names. This is by convention in the Python world. If you shop around at http://www.python.org, you'll find other free software that follows this pattern too: PyApache (a Python interface to the Apache web server), PySol (a Python/Tkinter solitaire game system), and many more. I'm not sure who started this pattern, but it has turned out to be a more or less subtle way to advertise programming language preferences to the rest of the open source world. Pythonistas are nothing if not subtle.

As in Chapter 4, and Chapter 5, I've pulled the examples in this chapter from my own library of Python programs that I really use. For instance, the text editor and clock GUIs that we'll meet here are day-to-day workhorses on my machines. Because they are written in Python and Tkinter, they work unchanged on both my Windows and Linux machines, and they should work on Macs, too.

And since these are pure Python scripts, their future evolution is entirely up to their users -- once you get a handle on Tkinter interfaces, changing or augmenting the behavior of such programs by editing their Python code is a snap. Although some of these examples are similar to commercially available programs (e.g., PyEdit is reminiscent of the Windows Notepad accessory), the portability and almost infinite configurability of Python scripts can be a decided advantage.

9.1.1 Examples in Other Chapters

Later in the book, we'll meet other Tkinter GUI programs that put a good face on specific application domains. For instance, the following larger GUI examples show up in later chapters, too:

• PyMail -- an email client in Chapter 11
• PyForm -- a persistent object table viewer in Chapter 16
• PyTree -- a tree data structure viewer in Chapter 17
• PyCalc -- a calculator widget in Chapter 18

Most of these programs see regular action on my desktop, too. Because GUI libraries are general-purpose tools, there are few domains that cannot benefit from an easy-to-use, easy-to-program, and widely portable user interface coded in Python and Tkinter.

Beyond the examples in this book, you can also find higher-level GUI toolkits for Python, such as the PMW system mentioned in Chapter 6. Such systems build upon Tkinter to provide compound components such as notebook and tabbed widgets. We'll also later meet programs that build user interfaces in web browsers, not Tkinter. But apart from simple web-based interfaces, Tkinter GUIs can be an indispensable feature of almost any Python program you write.

9.1.2 This Chapter's Strategy

As for all case-study chapters in this text, this one is largely a "learn by example" exercise; most of the programs here are listed with minimal details. Along the way I'll point out new Tkinter features that each example introduces, but I'll also assume that you will study the listed source code and its comments for more details. Python's readability becomes a substantial advantage for programmers (and writers), especially once we reach the level of complexity demonstrated by programs here.

Finally, I want to remind you that all of the larger programs listed in the previous sections can be run from the PyDemos and PyGadgets launcher-bar GUIs that we met at the end of the previous chapter. Although I will try hard to capture some of their behavior in screen shots here, GUIs are event-driven systems by nature, and there is nothing quite like running one live to sample the flavor of its user interactions. Because of that, the launcher bars are really a supplement to the material in this chapter. They should run on most platforms and are designed to be easy to start (see the top-level README-PP2E.txt file for hints). You should go there and start clicking things immediately, if you haven't done so already.