Rapid Application Development with Python and Glade
GladeGen first determines whether the specified module/file exists; if not, it creates a basic file with author information and a class definition. GladeGen then parses the Glade XML file and finds a list of widgets and handlers. Python provides the inspect module that allows a program to determine what functions, classes and methods an existing Python module contains and which lines correspond to each. GladeGen uses the inspect module to determine which callbacks have been written already so that they are not replaced with an empty callback method. GladeGen adds any new callbacks to the bottom of the class definition. The inspect module also allows GladeGen to determine which lines contain the init method and to replace them with a new init method containing all the widgets and handlers in the latest Glade XML file.
Python supports both the standard DOM and SAX interfaces for parsing XML files. The SAX interface is an event-driven model in which the user sets up functions to be called as XML tags are processed. The DOM interface reads the entire XML file into memory and provides functions for traversing the XML hierarchy and retrieving the information. For GladeGen, we wanted to extract only certain information from the XML file, so the DOM interface is simpler to use. Also, the size of a Glade XML file is small enough that reading the entire file into memory and generating the Python representation of it should not require a large amount of memory. Using the DOM interface, the get_xml method in the GladeGen class extracts the widget names and handler names from a Glade XML file using about 30 lines of Python code.
Glade and GladeGen automate much of the tedious, repetitive work that goes into creating graphical programs by removing the need to write code to create and store widgets and set up the callback functions. This allows for rapid application development of Python/GNOME/GTK applications. The finished Math Flash is shown in Figure 2. The GladeGen software can run on any system that supports Python and GTK, including Linux, UNIX, Mac OS X and Microsoft Windows.
A number of features could be added to this system. Instead of using the generic *args parameter for the created callback functions, the parameters could be specified explicitly, based on the widget and callback prototype. I also plan to add a graphical front end to the program for configuring the options in the GladeGenConfig.py file. The GladeGen software is released under the GPL. If anyone is interested in modifying/extending it, please let the author know.
Thanks to one of my students, Jeremiah Schilens, who worked on an earlier version of this project with me.
Resources for this article: /article/7558.
David Reed lives in Columbus, Ohio with his wife and two dogs. He has worked with UNIX systems since 1991 and Linux since 1997. He holds a PhD in volumetric graphics from The Ohio State University and currently teaches computer science at Capital University. Capital uses a mixture of Python, C++ and Java throughout its CS curriculum. David can be reached at email@example.com.
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