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.
So that's what an error looks like. And now that you've seen what makes it tick, how about writing something to handle it?
Zope allows you to trap errors using the standard "try-catch" exception-handling combination...or, in the DTML world, <dtml-try> and <dtml-catch>. Here's what it looks like:
<dtml-try>
execute this block
<dtml-except err>
execute this block if
exception "err" is raised
</dtml-try>
Take a look at this rewrite of the previous example, which incorporates a simple exception handler.
<dtml-try>
<dtml-var CheckThisOut><dtml-except><b>Something bad happened</b></dtml-try>
Now, view this DTML Document and you'll see that the ugly error screen has disappeared; it's been replaced by a simpler (though not very useful) error message.
The first part of the code introduces you to the <dtml-try> block; this tag instructs Zope to try - literally - to execute the statements within the enclosing block.
<dtml-try>
<dtml-var CheckThisOut>...</dtml-try>
The <dtml-except> tag sets up the exception handler, in the event that one is generated. This tag does the hard work of trapping the exception and suggesting an alternative path for Zope to proceed with.
<dtml-except>
<b>Something bad happened</b>
If an exception is generated, the <dtml-except> segment of the code will be triggered, and Zope's default error handling mechanism will be overridden by the instructions in that code segment - in this case, displaying the text "Something bad happened".
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