Beginning Python - From Novice to Professional

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CHAPTER 12 ■ ■ ■ Graphical User Interfaces In this chapter, you learn how to make graphical user interfaces (GUIs) for your Python programs: you know, windows with buttons and text fields and stuff like that. Pretty cool, huh? There are plenty of so-called “GUI toolkits” available for Python, but none of them is recognized as the standard GUI toolkit. This has its advantages (greater freedom of choice) and drawbacks (others can’t use your programs unless they have the same GUI toolkit installed; fortunately, there is no conflict between the various GUI toolkits available for Python, so you can install as many different GUI toolkits as you want). This chapter focuses on one of the most mature cross-platform GUI toolkits for Python, called wxPython. An Example GUI Application To make things easier to follow, I use a running example throughout this chapter. Your task is to write a basic program that enables you to edit text files. Writing a full-fledged text editor is beyond the scope of this chapter—we’ll stick to the essentials. After all, the goal is to demonstrate the basic mechanisms of GUI programming in Python. The requirements for this minimal text editor are as follows: • It must allow you to open text files, given their file names. • It must allow you to edit the text files. • It must allow you to save the text files. • It must allow you to quit. When writing a GUI program, it’s often useful to draw a sketch of how you want it to look. Figure 12-1 shows a simple layout that satisfies the requirements. 269
270 CHAPTER 12 ■ GRAPHICAL USER INTERFACES Figure 12-1. A sketch of the text editor The elements of the interface can be used as follows: 1. Type a file name in the text field to the left of the buttons and click Open to open a file. The text contained in the file is put in the text field at the bottom. 2. You can edit the text to your heart’s content in the large text field. 3. If and when you want to save your changes, click the Save button, which again uses the text field containing the file name—and writes the contents of the large text field to the file. 4. There is no Quit button—if the user closes the window, the program quits. In some languages, writing a program like this is a daunting task, but with Python and the right GUI toolkit, it’s really a piece of cake. (You may not agree with me right now, but by the end of this chapter I hope you will.) A Plethora of Platforms Before writing a GUI program in Python, you have to decide which GUI platform you want to use. Simply put, a platform is one specific set of graphical components, accessible through a given Python module, called a GUI toolkit. There are many such toolkits available for Python. Some of the most popular ones are listed in Table 12-1. For an even more detailed list, you could search the Vaults of Parnassus (see Appendix C) for the keyword “GUI.” Cameron Laird
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Beginning Python From Novice to Pro
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About the Technical Reviewer ■JER
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Introduction A C program is like a
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Index ■Symbols - operator 558 !=
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