Programming Python, 3rd Edition

Refactoring Code for Maintainability

Let’s step back from coding details for just a moment to gain some design perspective. As we’ve seen, Python code, by and large, automatically lends itself to systems that are easy to read and maintain; it has a simple syntax that cuts much of the clutter of other tools. On the other hand, coding styles and program design can often affect maintainability as much as syntax. For example, the “Hello World” selector pages of the preceding section work as advertised and were very easy and fast to throw together. But as currently coded, the languages selector suffers from substantial maintainability flaws.

Imagine, for instance, that you actually take me up on that challenge posed at the end of the last section, and attempt to add another entry for COBOL. If you add COBOL to the CGI script’s table, you’re only half done: the list of supported languages lives redundantly in two places—in the HTML for the main page as well as in the script’s syntax dictionary. Changing one does not change the other. More generally, there are a handful of ways that this program might fail the scrutiny of a rigorous code review. These are described next.

Selection list

As just mentioned, the list of languages supported by this program lives in two places: the HTML file and the CGI script’s table.

Field name

The field name of the input parameter, language, is hardcoded into both files as well. You might remember to change it in the other if you change it in one, but you might ...