Ever wondered if there was a way to stop Zope from barfing error messages all over your screen when one of your scripts crashes and burns? Well, guess what - there is! Meet the and tags, which can be used to trap and resolve errors in script execution.
As a developer, there are a few things you get used to pretty quickly: the long hours, the demanding customers, the low pay, the lack of a social life. However, if you're anything like most developers, there's one thing that probably never fails to get your goat, no matter how long you've been writing code.
It's sad but true - error-free code is still largely a Utopian dream. No matter how careful you are, no matter how deep your knowledge or how good your IDE, you're bound to slip up sooner or later. And when you do, and your routines decide to go AWOL, you need to take remedial action.
Most programming languages - including DTML - come with built-in exception handling capabilities. These exception handlers make it possible to catch errors and resolve them sensibly, thereby insulating the user from complex decisions and incomprehensible technical information. As a professional developer, you should always wrap your code in exception handling routines, if only to avoid embarrassing flameouts in front of your customers.
That's where this article comes in. Over the next few pages, I'm going to be looking at exception handling, with a special focus on exceptions in the Zope and DTML universe. I'll be explaining the most common error types you'll encounter, together with the DTML constructs you can use to catch and resolve them, and I'll include lots of examples so that you can see how it works in practice. So come on in, and let's get started.