The Insider's Best-Practice Guide to Rapid PyQt 4 GUI Development
Whether you're building GUI prototypes or full-fledged cross-platform GUI applications with native look-and-feel, PyQt 4 is your fastest, easiest, most powerful solution. Qt expert Mark Summerfield has written the definitive best-practice guide to PyQt 4 development.
With Rapid GUI Programming with Python and Qt you'll learn how to build efficient GUI applications that run on all major operating systems, including Windows, Mac OS X, Linux, and many versions of Unix, using the same source code for all of them. Summerfield systematically introduces every core GUI development technique: from dialogs and windows to data handling; from events to printing; and more. Through the book's realistic examples you'll discover a completely new PyQt 4-based programming approach, as well as coverage of many new topics, from PyQt 4's rich text engine to advanced model/view and graphics/view programming. Every key concept is illuminated with realistic, downloadable examples—all tested on Windows, Mac OS X, and Linux with Python 2.5, Qt 4.2, and PyQt 4.2, and on Windows and Linux with Qt 4.3 and PyQt 4.3.
- Python basics for every PyQt developer: data types, data structures, control structures, classes, modules, and more
- Core PyQt GUI programming techniques: dialogs, main windows, and custom file formats
- Using Qt Designer to design user interfaces, and to implement and test dialogs, events, the Clipboard, and drag-and-drop
- Building custom widgets: Widget Style Sheets, composite widgets, subclassing, and more
- Making the most of Qt 4.2's new graphics/view architecture
- Connecting to databases, executing SQL queries, and using form and table views
- Advanced model/view programming: custom views, generic delegates, and more
- Implementing online help, internationalizing applications, and using PyQt's networking and multithreading facilities
About the Author
Mark Summerfield works as an independent trainer and consultant specializing in C++, Qt, Python, and PyQt. He was Trolltech’s documentation manager from 2000 to 2004, was the founding editor of Qt Quarterly, Trolltech’s customer newsletter, and coauthored C++ GUI Programming with Qt 3 and C++ GUI Programming with Qt 4.Excerpt. © Reprinted by permission. All rights reserved.
This book teaches how to write GUI applications using the Python programming language and the Qt application development framework. The only essential prior knowledge is that you can program in some object-oriented programming language, such as C++, C#, Java, or of course, Python itself. For the rich text chapter, some familiarity with HTML and with regular expressions is assumed, and the databases and threading chapters assume some basic knowledge of those topics. A knowledge of GUI programming is not required, since all the key concepts are covered.
The book will be useful to people who program professionally as part of their job, whether as full-time software developers, or those from other disciplines, including scientists and engineers, who need to do some programming in support of their work. It is also suitable for undergraduate and post-graduate students, particularly those doing courses or research that includes a substantial computing element. The exercises (with solutions) are provided especially to help students.
Python is probably the easiest to learn and nicest scripting language in widespread use, and Qt is probably the best library for developing GUI applications. The combination of Python and Qt, "PyQt", makes it possible to develop applications on any supported platform and run them unchanged on all the supported platforms--for example, all modern versions of Windows, Linux, Mac OS X, and most Unix-based systems. No compilation is required thanks to Python being interpreted, and no source code changes to adapt to different operating systems are required thanks to Qt abstracting away the platform-specific details. We only have to copy the source file or files to a target machine that has both Python and PyQt installed and the application will run.
If you are new to Python: Welcome! You are about to discover a language that is clear to read and write, and that is concise without being cryptic. Python supports many programming paradigms, but because our focus is on GUI programming, we will take an object-oriented approach everywhere except in the very early chapters.
Python is a very expressive language, which means that we can usually write far fewer lines of Python code than would be required for an equivalent application written in, say, C++ or Java. This makes it possible to show some small but complete examples throughout the text, and makes PyQt an ideal tool for rapidly and easily developing GUI applications, whether for prototyping or for production use.
Since the emphasis of the book is on GUI programming, Part I provides a fast-paced Python tutorial as well as some PyQt coverage. This material is clearly marked to make it easy for experienced Python programmers to skip the Python they already know. Parts II, III, and IV of the book are all PyQt-specific and assume that readers can already program in Python, whether from previous experience or from reading Part I.
Quite often in programming we reach decision points when there are several possible approaches we could take. Reference books and the online documentation identify what classes, methods, and functions are available, and in some cases provide examples, but such documents rarely provide a broader context. This book gives the necessary context, highlighting the key decision points for GUI programming and offering insights into the pros and cons so that you can decide for yourself what the right policy is for your particular circumstances. For example, when you create a dialog, should it be modal or modeless? (See Chapter 5 for an explanation and policy recommendations on this issue.)
PyQt is used to write all kinds of GUI applications, from accounting applications, to visualization tools used by scientists and engineers. Figure 1, for example, shows Eric, a powerful integrated development environment that is written in PyQt. It is possible to write PyQt applications that are just tens of lines long, and medium-size projects of 1000 to 10000 lines are very common. Some commercial companies have built 100,000-line PyQt applications, with programming teams varying in size from just one person to more than a dozen people. Many in-house tools are written using PyQt, but because these are often used to gain competitive advantage, the companies involved generally do not permit their use of PyQt to be made public. PyQt is also widely used in the open source world, with games, utilities, visualization tools, and IDEs all written using it.
This book is specifically about PyQt4, the Python bindings for the Qt 4 C++ application development framework. PyQt4 is provided in the form of ten Python modules which between them contain around 400 classes and about 6000 methods and functions. All the example programs have been tested on Windows, Linux, and Mac OS X, using Python 2.5, Qt 4.2, and PyQt 4.2, and additionally on Windows and Linux using Qt 4.3 and PyQt 4.3. Backporting to earlier versions is possible in some cases, but we recommend using the most up-to-date versions of Python, Qt, and PyQt.
Python, PyQt, and Qt can be used free of charge for noncommercial purposes, but the license used by Python is different from that used by PyQt and Qt. Python is available with a very liberal license that allows it to be used to develop both commercial and noncommercial applications. Both PyQt and Qt are dual-licensed: This essentially allows them to be used to develop noncommercial applications--which must in turn be licensed using an acceptable open source license such as the GNU General Public License (GPL); or to be used to develop commercial applications--in this case, a commercial PyQt license and a commercial Qt license must be purchased.
The Structure of the Book
The book is divided into four parts. Part I is primarily a rapid conversion course aimed at non-Python programmers who are familiar with an object-oriented language, although it also has some (clearly marked) PyQt content. Because the core Python language is mostly simple and is quite small, these chapters can teach the basics of Python to a sufficient extent that real Python applications can be written.
If you think that you can pick up the Python syntax simply through reading it, you might be tempted to skip Part I and dive straight into the GUI programming that begins in Part II. The early chapters in Part II include back-references to the relevant pages in Part I to support readers who choose this approach. However, even for readers familiar with Python, we recommend reading about QString in Chapter 1. If you are unfamiliar with partial function application (currying), it is important to read the subsection that covers this in Chapter 2, since this technique is sometimes used in GUI programming.
There are also Python bindings for the older Qt 3 library, but there is no reason to use that library for new projects, especially since Qt 4 offers far more functionality and is easier to use.
Part II begins by showing three tiny PyQt GUI applications to give an initial impression of what PyQt programming is like. It also explains some of the fundamental concepts involved in GUI programming, including PyQt's high-level signals and slots communication mechanism. Chapter 5 shows how to create dialogs and how to create and lay out widgets ("controls" in Windows-speak--the graphical elements that make up a user interface such as buttons, listboxes,and such) in a dialog. Dialogs are central to GUI programming: Most GUI applications have a single main window, and dozens or scores of dialogs, so this topic is covered in depth.
After the dialogs chapter comes Chapter 6, which covers main windows, including menus, toolbars, dock windows, and keyboard shortcuts, as well as loading and saving application settings. Part II's final chapters show how to create dialogs using Qt Designer, Qt's visual design tool, and how to save data in binary, text, and XML formats.
Part III gives deeper coverage of some of the topics covered in Part II, and introduces many new topics. Chapter 9 shows how to lay out widgets in quite sophisticated ways, and how to handle multiple documents. Chapter 10 covers low-level event handlers, and how to use the clipboard as well as drag and drop, text, HTML, and binary data. Chapter 11 shows how to modify and subclass existing widgets, and how to create entirely new widgets from scratch, with complete control over their appearance and behavior. This chapter also shows how to do basic graphics. Chapter 12 shows how to use Qt 4.2's new graphics/view architecture, which is particularly suited to handling large numbers of independent graphical objects. Qt's HTML-capable rich text engine is covered in Chapter 13. This chapter also covers printing both to paper and to PDF files.
Part III concludes with two chapters on model/view programming: Chapter 14 introduces the subject and shows how to use Qt's built-in views and how to create custom data models and custom delegates, and Chapter 15 shows how to use the model/view architecture to perform database programming.
Part IV continues the model/view theme, with coverage of three different advanced model/view topics in Chapter 16. The first section of Chapter 17 describes the techniques that can be used for providing online help, and the second section explains how to internationalize an application, including how to use Qt's translation tools to create translation files. The Python standard library provides its own classes for networking and for threading, but in the last two chapters of Part IV we show how to do networking and threading using PyQt's classes.
Appendix A explains where Python, PyQt, and Qt can be obtained, and how to install them on Windows, Mac OS X, and Linux. PyQt is much easier to learn if you install it and try out some of the exercises, and if you inspect some of the example code. Appendix B presents screenshots and brief descriptions of selected PyQt widgets; this is helpful for those new to GUI programming. Appendix C presents diagrams of some of PyQt's key class hierarchies; this is useful for getting to know what ...