Python GUI Development Options






Python GUI Development Options

Before we start wading into the Tkinter pond, let's begin with some perspective on Python GUI options in general. Because Python has proven to be such a good match for GUI work, this domain has seen much activity in recent years. In fact, although Tkinter is the most widely used GUI toolkit in Python, there are a variety of ways to program user interfaces in Python today. Some are specific to Windows or X Windows,[*] some are cross-platform solutions, and all have followings and strong points of their own. To be fair to all the alternatives, here is a brief inventory of GUI toolkits available to Python programmers as I write these words:

[*] In this book, "Windows" refers to the Microsoft Windows interface common on PCs, and "X Windows" refers to the X11 interface most commonly found on Unix and Linux platforms. These two interfaces are generally tied to the Microsoft and Unix platforms, respectively. It's possible to run X Windows on top of a Microsoft operating system and Windows emulators on Unix and Linux, but it's not common.


Tkinter

An open source GUI library and the continuing de facto standard for portable GUI development in Python. Python scripts that use Tkinter to build GUIs run portably on Windows, X Windows (Unix and Linux), and Macintosh (both classic and OS X), and they display a native look-and-feel on each of these. Tkinter makes it easy to build simple and portable GUIs quickly. Moreover, it can be easily augmented with Python code, as well as with larger extension packages such as Pmw (a third-party widget library), Tix (another widget library, and now a standard part of Python), and PIL (an image-processing extension).

The underlying Tk library used by Tkinter is a standard in the open source world at large and is also used by the Perl, Ruby, PHP, and Tcl scripting languages, giving it a user base that numbers in the millions. The Python binding to Tk is enhanced by Python's simple object model; Tk widgets become customizable and embeddable objects, not string commands.

Tkinter is mature, robust, widely used, and well documented. It includes roughly 25 basic widget types, plus various dialogs and other tools. Moreover, there is a dedicated book on the subject, plus a large library of published Tkinter and Tk documentation. Perhaps most importantly, because it is based on a library developed for scripting languages, Tkinter is also a relatively lightweight toolkit, and as such it meshes well with a scripting language like Python.

Because of such attributes, Python's Tkinter module ships with Python as a standard library module and is the basis of Python's standard IDLE integrated development environment GUI. In fact, Tkinter is the only GUI toolkit that is part of Python; all others on this list are third-party extensions. The underlying Tk library is also shipped with Python on some platforms (including Windows and most Linux systems).

Although Tkinter is easy to use, its text and canvas widgets are powerful enough to implement web pages, three-dimensional visualization, and animation. PythonWorks, Komodo, and others provide GUI builders for Tkinter, and some Tk tools work for Python too; as we will see, though, Tkinter is usually so easy to code that GUI builders are not widely used.


wxPython

A Python interface for the open source wxWidgets (formerly called wxWindows[*]) library, a portable GUI class framework originally written to be used from the C++ programming language. The wxPython system is an extension module that wraps wxWindows classes. This library is generally considered to excel at building sophisticated interfaces and is probably the second most popular Python GUI toolkit today, behind Tkinter. Today, wxPython code is portable to Windows, Unix-like platforms, and Mac OS X.

[*] Per an article that appeared on slashdot.org in 2004, the name of the underlying wxWidgets library was changed from wxWindows in response to a "polite request" by Microsoft.

Because wxPython is based on a C++ class library, it is generally more complex than Tkinter: it provides more than 200 classes at last count, requires an object-oriented coding style, and has a design reminiscent of MFC. wxPython often expects programmers to write more code, partly because it is a more complex system and partly because it inherits this mindset from its underlying C++ library.

Moreover, wxPython is not as well documented as Tkinter: some of its documentation is oriented toward C++, and there are no books dedicated to wxPython as I write these words. By contrast, Tkinter is covered by one book dedicated to it, large sections of other Python books, and an even larger library of existing literature on the underlying Tk toolkit. (After I wrote this paragraph, a wxPython book was preannounced, but it is still under development and will likely be the only Python-specific wxPython resource available for some time to come.)

On the other hand, in exchange for its added complexity, wxPython provides a powerful toolkit. wxPython comes with a richer set of widgets out of the box than Tkinter, including trees and HTML viewersthings that require extensions such as Pmw or Tix in Tkinter. In addition, some prefer the appearance of the interfaces it renders. BoaConstructor and wxDesigner, among other options, provide a GUI builder that generates wxPython code. Some wxWidgets tools also support Python work. For a quick look at wxPython widgets and code, run the demo that comes with the system.


PyQt

A Python interface to Qt, perhaps the third most widely used GUI toolkit for Python today. PyQt is a full-featured GUI library and runs portably today on Windows, Mac OS X, and Unix and Linux (including the Zaurus Linux-based PDA). Qt is generally more complex, yet more feature rich, than Tkinter as well; it currently contains 300 classes and more than 5,750 functions and methods. Perhaps its most widely cited drawback is that it is not completely open source for commercial use. (Qt 4, announced after this chapter was written, now provides both GPL and commercial license versions on all platforms, including Windows. The GPL version is open source, but also imposes requirements beyond those of the Python BSD-style license; you must, for example, make your source code freely available to end users under the GPL unless you purchase a commercial license instead.) Qt grew up on Linux; the PyQt and PyKDE extension packages provide access to KDE development libraries (PyKDE requires PyQt). The BlackAdder and Qt Designer systems provide a GUI builder for PyQt.


PyGTK

A Python interface to GTK, a portable GUI library originally used as the core of the Gnome window system on Linux. The gnome-python and PyGTK extension packages export Gnome and GTK toolkit calls. At this writing, PyGTK runs portably on Windows and POSIX systems such as Linux and Mac OS X (provided that an X server for Mac OS X has been installed, though a native version is in the works).


Jython

As we will see in Chapter 18, Jython (the system formerly known as JPython) is a Python port for Java, which gives Python scripts seamless access to Java class libraries on the local machine. Because of that, Java GUI libraries such as swing and awt become another way to construct GUIs in Python code run by the JPython system. Such solutions are obviously Java specific and limited in portability to the portability of Java and its libraries. Furthermore, swing is likely the largest and most complex GUI option for Python work. A new package named jTkinter also provides a Tkinter port to Jython using Java's JNI; if installed, Python scripts may also use Tkinter to build GUIs under JPython.


MFC

The Windows PyWin32 extensions package for Python, available at Python's web site, includes wrappers for the Microsoft Foundation Classes (MFC) frameworka development library that includes user interface components. With the Windows extensions, Python programs can construct Windows GUIs using the same MFC calls applied in languages such as Visual C++. Pythonwin, an MFC sample program that implements a Python development GUI, is included with the extensions package. This is a Windows-only solution, but it may be an appealing option for developers with a prior intellectual investment in using the MFC framework from Visual C++.


PythonCard

An open source GUI builder and library built on top of the wxPython toolkit and considered by some to currently be Python's closest equivalent to GUI builders such as those familiar to Visual Basic developers. PythonCard describes itself as a GUI construction kit for building cross-platform desktop applications on Windows, Mac OS X, and Linux, using the Python language.


Dabo

An emerging open source GUI builder also built on wxPython, and a bit more. Dabo is a portable, three-tier, cross-platform application development framework, inspired by Visual FoxPro and written in Python. Its tiers support database access, business logic, and user interface. Its open design is intended to eventually support a variety of databases and multiple user interfaces (wxPython, Tkinter, and even HTML over HTTP).


AnyGui

A toolkit that aims to provide an API that is portable across a variety of underlying toolkits, including Tkinter, wxPython, and Qt. This API takes a lowest-common-denominator approach to achieve its portability. (As of this writing, AnyGui is no longer being actively developed and serves mostly as a proof-of-concept project.)


WPY

An MFC-like GUI library for Python, ported to run on both X Windows for Unix (where it uses Tk) and Windows for PCs (where it uses MFC). WPY scripts run unchanged on each platform, but they use MFC coding styles.


Others

On Macintosh OS X platforms, Python scripts can use the Cocoa library. For Unix-like systems, interfaces to the raw X Windows and Motif libraries also exist for Python; they provide maximum control over the X11 development environment but are an X-only solution.

See the web sites of these toolkits for more details. There are other lesser-known GUI toolkits for Python, and new ones are likely to emerge by the time you read this book (e.g., the IronPython Python port to the .NET Framework on Windows may offer user interface options as well). Moreover, packages like those in this list mutate over time. For an up-to-date list of available tools, see http://www.python.org and the Vaults of Parnassus third-party packages site, currently at http://www.vex.net/parnassus.[*]

[*] In Part IV, we'll also learn how to build basic user interfaces within a web browser, using HTML and Python scripts that run on a server. For now, we'll focus on more traditional GUIs that may or may not be connected to a network.



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