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This chapter is the fourth part of our look at Python Internet programming, and continues the last chapter's discussion. In the prior chapter, we explored the fundamentals of server-side CGI scripting in Python. Armed with that knowledge, in this and the following chapter we move on to two larger case studies that underscore advanced CGI topics:

PyMailCgi

This chapter presents PyMailCgi,a web site for reading and sending email that illustrates security concepts, hidden form fields, URL generation, and more. Because this system is similar in spirit to the PyMailGui program shown in Chapter 11, this example also serves as a comparison of web and non-web applications.

PyErrata

Chapter 14, presents PyErrata, a web site for posting book comments and bugs that introduces database concepts in the CGI domain. This system demonstrates common ways to store data persistently on the server between web transactions, and addresses concurrent update problems inherent in the CGI model.

Both of these case studies are based on CGI scripting, but implement full-blown web sites that do something more useful than the last chapter's examples.

As usual, these chapters split their focus between application-level details and Python programming concepts. Because both of the case studies presented are fairly large, they illustrate system design concepts that are important in actual projects. They also say more about CGI scripts in general. PyMailCgi, for example, introduces the notions of state retention in hidden fields and URLs, as well as security concerns and encryption. PyErrata provides a vehicle for exploring persistent database concepts in the context of web sites.

Neither system here is particularly flashy or feature-rich as web sites go (in fact, the initial cut of PyMailCgi was thrown together during a layover at a Chicago airport). Alas, you will find neither dancing bears nor blinking lights at either of these sites. On the other hand, they were written to serve real purposes, speak more to us about CGI scripting, and hint at just how far Python server-side programs can take us. In Chapter 15, we will explore higher-level systems and tools that build upon ideas we will apply here. For now, let's have some fun with Python on the Web.