Python & XML

Chapter 1. Python and XML

Python and XML are two very different animals, each with a rich history. Python is a full-scale programming language that has grown from scripting world roots in a very organic way, through the vision and guidance of Python’s inventor, Guido van Rossum. Guido continues to take into account the needs of Python developers as Python matures. XML, on the other hand, though strongly impacted by the ideas of a small cadre of visionaries, has grown from standards-committee roots. It has seen both quiet adoption and wrenching battles over its future. Why bother putting the two technologies together?

Before the Python/XML combination, there seemed no easy or effective way to work with XML in a distributed environment. Developers were forced to rely on a variety of tools used in awkward combination with one other. We used shell scripting and Perl to process text and interact with the operating system, and then used Java XML API’s for processing XML and network programming. The shell provided an excellent means of file manipulation and interaction with the Unix system, and Perl was a good choice for simple text manipulation, providing access to the Unix APIs. Unfortunately, neither sported a sophisticated object model. Java, on the other hand, featured an object-oriented environment, a robust platform API for network programming, threads, and graphical user interface (GUI) application development. But with Java, we found an immediate lack of text manipulation power; scripting languages typically provided strong text processing. Python presented a perfect solution, as it combines the strengths of all of these various options.

Like most scripting languages, Python features excellent text and file manipulation capabilities. Yet, unlike most scripting languages, Python sports a powerful object-oriented environment with a robust platform API for network programming, threads, and graphical user interface development. It can be extended with components written in C and C++ with ease, allowing it to be connected to most existing libraries. To top it off, Python has been shown to be more portable than other popular interpreted languages, running comfortably on platforms ranging from massive parallel Connection Machines to personal digital assistants and other embedded systems. As a result, Python is an excellent choice for XML programming and distributed application development.

It could be said that Python brings sanity and robustness to the scripting world, much in the same way that Java once did to the C++ world. As always, there are trade-offs. In moving from C++ to Java, you find a simpler language with stronger object-oriented underpinnings. Changing to a simpler language further removed from the low-level details of memory management and the hardware, you gain robustness and an improved ability to locate coding errors. You also encounter a rich API equipped with easy thread management, network programming, and support for Internet technologies and protocols. As may be expected, this flexibility comes at a cost: you also encounter some reduced performance when comparing it with languages such as C and C++.

Likewise, when choosing a scripting language such as Python over C, C++, or even Java, you do make some concessions. You trade performance for robustness and for the ability to develop more rapidly. In the area of enterprise and Internet systems development, choosing reliable software, flexible design, and rapid growth and deployment are factors that outweigh the performance gains you might get by using a language such as C++. If you do need some of the performance back, you can still implement speed-sensitive components of your application in C or C++, but you can avoid doing so until you have profiling data to help you pinpoint what is really a problem and what only might be a problem. (How to perform the analysis and write extensions in C/C++ is a topic for other books.)

Regardless of your feelings on scripting languages, Java, or C++, this book focuses on XML and the Python language. For those who are new to XML, we will start with an overview of why it is interesting, and then we’ll move on to using it from Python and seeing how we make our XML applications easier to create.