Friday, August 25, 2006

Spyce will not waste your time: form processing

The revamed Spyce website announces "Spyce will not waste your time."

Most web frameworks today waste your time with busywork at least some of the time. This is unacceptable; boilerplate code is tedious to write, an obstacle to good maintenance, and a distraction from real productivity. All the development of Spyce 2.0 and 2.1 has been towards eliminating common sources of busywork in web development.

Today I'll give a couple concrete examples of how this applies to creating forms for user input.

Let's say you want to have a select box that remembers what the user's last selection was. Pretty much any form these days needs logic like this when giving feedback inline. Many frameworks make you write this code out by hand; if you've ever developed in one of these, you know how quickly this gets old.

Here's what you'd have to write in Spyce 2.1, given a list of options named options:

<f:select name="foo" data="options" />

That's it.

For comparison, here's what this would have looked like in Spyce version 1.2, some time in 2002. Many frameworks still make you do it much the same way today:

<select name="foo">
  [[ for name, value in options:{ ]]
     <option value="[[= value ]]"[[ if value == request['foo']:{ ]] selected[[ } ]]>[[= name ]]</option>
  [[ } ]]

Going back to the modern Spyce: notice the data attribute? All Spyce tags that you would expect to use a for loop with, now take a data attribute that can be any Python iterable. You can still render the contents of a select or a ul or a table manually, but Spyce saves you time for the common case.

Spyce also takes the boilerplate out of giving feedback to users. I'm unaware of any other framework that makes this as easy as Spyce; perhaps the closest is ASP.NET, but even that seems pretty clunky to me after using Spyce for a while.

All you need to do is raise a HandlerError from your handler, and Spyce knows how to render it with the associated form with no further action on your part:

    raise HandlerError('choice', 'None selected')

The rendering of errors is easily customized, and you can raise CompoundHandlerError if there's more than one problem.

There's a live example over here; click on "Run this code" and see what it does when you ask for the square root of a negative number.

I'll leave comparing this with the hoops your current framework makes you jump through as an exercise for the reader.


Anonymous said...

I see and understand the example; what sort of error handling is possible in a multi-field form, using out of the box form handling as opposed to hand crafted?

Will errors be trapped field by field (and presented with helpful error text hints along side or under each field)? Or will the user have to step through the form submit by submit, correcting each error in sequence as they are alerted? A multi-field example showing error handling might be nice...

Jonathan Ellis said...

Here is an example showing CompoundHandlerError:

Anonymous said...

I would be cool if handlers could execute some abitrary javascript. Maybe if i did a redirect to a page with the js in it?
I have not used the heandlers as much as i wanted since most of my stuff calls AJAX stuff (openrico , mochikit)
I seem to remember this being possible in the 1.3 days??

Jonathan Ellis said...

You can't really do AJAX with handlers in Spyce 2.1; it's something we'd like to do for 2.2. (Even if you redirected to a page with js, you're already committed to the page load, which defeats the point if I understand your scenario correctly.)

Handlers were introduced in 2.0, so no, you're not remembering 1.3 incorrectly. :)