ZPT Basics (part 1) (
Page 1 of 5 )
Contrary to what you might think, DTML isn't the only programming language available
to you in Zope. Take a look at Zope Page Templates (ZPT), a template-based alternative
that makes it easier for designers and developers to collaborate on Zope application
development.Not too long ago, I introduced you to something called DTML, the Document Template
Markup Language. I defined it as HTML on steroids, and spent lots of time and
bandwidth showing you how it could be used to build complex Zope applications.
DTML isn't the only thing Zope has going for it, though. Over the next few pages,
I'm going to introduce you to a brand-spanking-new creature from the Zope stable.
It's called Zope Page Templates, or ZPT, and it's rapidly overtaking DTML as the
de-facto standard for developing applications in Zope.
The Zope Web site is pretty wordy when it comes to describing ZPT. It defines
ZPT as "a consistent, XML compliant, markup language [which] embed[s] all logic
in namespaced attributes ...and provide[s] a means to supply prototypical content
to give the presentation designer a sense of context." Or, to put it in simpler
terms, ZPT allows Web developers greater flexibility in separating an application's
presentation layer from the business logic that drives it, thereby making it possible
to easily update one without disrupting the other.
I'm going to show you how in the following pages. Before I begin, though, make
sure that you have a working copy of Zope and ZPT (this tutorial uses Zope 2.5.0,
which comes with ZPT built in), and can log in to the Zope management interface.
In case you can't, drop by
http://www.zope.org/, get yourself set up and come back when you're ready to roll.{mospagebreak title=The
Right Choice} Let's start with a very basic, but important, question: why use
ZPT when you can use DTML?
There are a couple of reasons why you might prefer to use ZPT instead of DTML.
First, DTML isn't really all that friendly, even to developers who are used to
wading in the muddy waters of open-source programming languages. The language
comes with numerous idiosyncrasies, which can be both annoying and confusing to
developers. For example, the result value obtained from a DTML variable often
depends on the manner in which it is accessed, and the connectivity between DTML
and Python can often leave you confused and desperately searching for a Python
programmer to help you get unstuck.
In addition to the technical problems with DTML, it's also not perfect when it
comes to separating business logic from interface code. Since DTML documents contain
both HTML code and DTML commands, interface designers and developers must collaborate
closely with each other whenever a change needs to be made to the interface or
processing sequences within a DTML document. Obviously, this means more time and
effort to implement changes.
ZPT attempts to resolve this last problem by using templates to separate presentation
and layout information from program code. This two-tiered approach affords both
developers and designers a fair degree of independence when it comes to maintaining
a Zope application, and can substantially reduce the time and effort required
in the post-release phases of a development project.
Does this mean DTML is now redundant? No, not really. ZPT should not be considered
a replacement for DTML; rather, it should be treated as an alternative to DTML.
There still are some things that can be handled only using DTML - sending mail,
managing sequences, batching and so on. If you're planning on working with Zope,
you're going to need to keep your DTML skills current. It's just that you now
have a little more choice.
/ 22 
