Introduction

Credit: Andy McKay

The Web has been a key technology for many years now, and it has become unusual to develop an application that doesn't involve some aspects of the Web. From showing a help file in a browser to using web services, the Web has become an integral part of most applications.

I came to Python through a rather tortuous path of ASP (Active Server Pages), then Perl, some Zope, and then Python. Looking back, it seems strange that I didn't find Python earlier, but the dominance of Perl and ASP (and later PHP) in this area makes it difficult for new developers to see the advantages of Python shining through all the other languages.

Unsurprisingly, Python is an excellent language for web development, and, as a batteries included language, Python comes with most of the modules you need. The relatively recent inclusion of xmlrpclib in the Python Standard Library is a reassuring indication that batteries continue to be added as the march of technology requires, making the standard libraries even more useful. One of the modules I often use is urllib, which demonstrates the power of a simple, well-designed modulesaving a file from the Web in two lines (using urlretrieve) is easy. The cgi module is another example of a module that has enough functionality to work with, but not too much to make your scripts slow and bloated.

Compared to other languages, Python seems to have an unusually large number of application servers and templating languages. While it's easy to develop anything for the Web in Python "from scratch", it would be peculiar and unwise to do so without first looking at the application servers available. Rather than continually recreating dynamic pages and scripts, the community has taken on the task of building these application servers to allow other users to create the content in easy-to-use templating systems.

Zope is the most well-known product in this space and provides an object-oriented interface to web publishing. With features too numerous to mention, Zope allows a robust and powerful object-publishing environment. The new, revolutionary major release, Zope 3, makes Zope more Pythonic and powerful than ever. Quixote and WebWare are two other application servers with similar, highly modular designs. Any of these can be a real help to the overworked web developer who needs to reuse components and to give other users the ability to create web sites. The Twisted network-programming framework, increasingly acknowledged as the best-of-breed Python framework for asynchronous network programming, is also starting to expand into the web application server field, with its newer "Nevow" offshoot, which you'll also find used in some of the recipes in this chapter.

For all that, an application server is just too much at times, and a simple CGI script is really all you need. Indeed, the very first recipe, Recipe 14.1, demonstrates all the ingredients you need to make sure that your web server and Python CGI scripting setup are working correctly. Writing a CGI script doesn't get much simpler than this, although, as the recipe's discussion points out, you could use the cgi.test function to make it even shorter.

Another common web-related task is the parsing of HTML, either on your own site or on other web sites. Parsing HTML tags correctly is not as simple as many developers first think, as they optimistically assume a few regular expressions or string searches will see them through. However, we have decided to deal with such issues in other chapters, such as Chapter 1, rather than in this one. After all, while HTML was born with and for the Web, these days HTML is also often used in other contexts, such as for distributing documentation. In any case, most web developers create more than just web pages, so, even if you, the reader, primarily identify as a web developer, and maybe turned to this chapter as your first one in the book, you definitely should peruse the rest of the book, too: many relevant, useful recipes in other chapters describe parsing XML, reading network resources, performing systems administration, dealing with images, and many great ideas about developing in Python, testing your programs, and debugging them!