Head First Python, 2nd Edition

Chapter 11. Exception Handling: What to Do When Things Go Wrong

Things go wrong, all the time—no matter how good your code is.

You’ve successfully executed all of the examples in this book, and you’re likely confident all of the code presented thus far works. But does this mean the code is robust? Probably not. Writing code based on the assumption that nothing bad ever happens is (at best) naive. At worst, it’s dangerous, as unforeseen things do (and will) happen. It’s much better if you’re wary while coding, as opposed to trusting. Care is needed to ensure your code does what you want it to, as well as reacts properly when things go south. In this chapter, you’ll not only see what can go wrong, but also learn what to do when (and, oftentimes, before) things do.

Long Exercise

We’re starting this chapter by diving right in. Presented below is the latest code to the vsearch4web.py webapp. As you’ll see, we’ve updated this code to use the check_logged_in decorator from the last chapter to control when the information presented by the /viewlog URL is (and isn’t) visible to users.

Take as long as you need to read this code, then use a pencil to circle and annotate the parts you think might cause problems when operating within a production environment. Highlight everything that you think might ...