Home arrow Zope arrow DTML Basics (part 3)

DTML Basics (part 3)

Last time out, DTML Basics demonstrated conditional statements. This time around, it's time to study loops...which, in the DTML world, aren't exactly what you're used to. Take a look.

  1. DTML Basics (part 3)
  2. When In Rome...
  3. A List In Time
  4. An Easy Replacement
  5. Bringing In The Database
  6. Digging Deeper
By: Harish Kamath, (c) Melonfire
Rating: starstarstarstarstar / 5
July 02, 2002

print this article


If you've been following along, you now know how to incorporate decision-making constructs in your DTML code. As you saw in last week's episode, DTML comes with a fairly large family of conditional statements, which allow you to add business intelligence to your DTML scripts.

But DTML is a full-fledged programming language, and one which allows you to do a lot more than nest "if" statements within each other. One of its cooler capabilities involves using powerful loop constructs to iterate over sequences of both variables and objects. This ability to create loops is not unique to DTML - almost every programming language on the planet allows you to do this - but DTML includes some fairly interesting twists to the traditional approach.

Coincidentally, those twists just happen to be the subject of today's discussion. Keep reading - you've probably never seen this before.{mospagebreak title=Playing The Numbers} Before we get started, let's get the jargon straight - what's a sequence anyway?

As traditionally understood, a "sequence" is a series of items, usually connected to each other by a logical thread. For example,

0, 1, 2, 3, 4, 5...

p, q, r, s, t...

huey, dewey, louie...

are all valid sequences

In the Zope context, the definition of a sequence can be scoped down a little further - a sequence here is usually a set of objects. For example, if you create a folder in Zope, the objects stored within that folder can be considered a sequence. Or, if you retrieve a set of records from a database, the resultset returned can also be considered a sequence of data items.

A sequence, however, is just one part of the jigsaw. In order to access the elements that make up a sequence, you usually need a programming structure that will iterate, or loop, through the sequence, processing each element in turn. This loop can be combined with decision-making logic (remember what you learnt last time?) to perform specific actions or execute specific commands while processing the elements in a sequence.

In order to demonstrate this, let's create a sequence in Zope and write a loop to process it. Fire up Zope, log into the Zope management interface, and create an instance of the DTML Document object. Name it "SampleSequence" and fill it with the following code:

<h3><dtml-var title_or_id></h3><br> <ul> <dtml-in expr="0, 1, 2, 3, 4, 5"> <li> I am <dtml-var sequence-item></li> </dtml-in> </ul>
First, I've created a simple sequence by brute force - it contains numbers from 0 to 5. Then, the <dtml-in> tag is used to loop through the sequence, in a manner similar to the "for" loops that PHP and Perl programmers are familiar with. From the output, it's obvious that this script loops six times to display the items in the sequence.

The individual elements of the sequence can be accessed via the special "sequence-item" variable. This is true in all cases, except when the items in the sequence are object that cannot be converted to strings.

Save the code and view the output of the script - you should see something like this:

* I am 0 * I am 1 * I am 2 * I am 3 * I am 4 * I am 5

>>> More Zope Articles          >>> More By Harish Kamath, (c) Melonfire

blog comments powered by Disqus
escort Bursa Bursa escort Antalya eskort


- Creating Zope Products
- Plone Content Types With Archetypes
- Flat User Management in Zope
- Creating Basic Zope Applications
- Getting started with Zope for Linux and Sola...
- ZPT Basics (part 4)
- ZPT Basics (part 3)
- ZPT Basics (part 2)
- ZPT Basics (part 1)
- Exception Handling In DTML
- DTML Basics (part 4)
- DTML Basics (part 3)
- DTML Basics (part 2)
- DTML Basics (part 1)
- Using Zope With Apache

Developer Shed Affiliates


Dev Shed Tutorial Topics: