ZPT Basics (part 3) - When In Rome... (
Page 2 of 6 )
Not impressed yet? Let's alter the code a little to see what else
you can do with sequences.
<span tal:repeat="fruits python:'apple', 'banana', 'orange', 'apricot',
'grape'">
<i tal:condition="repeat/fruits/start">Here's where it all
starts</i> <br>
I am a <span tal:replace="fruits" />, my sequence
position is <span tal:replace="repeat/fruits/number"
/>,
and my index number is <span tal:replace="repeat/fruits/index" />. <br>
<i
tal:condition="repeat/fruits/end">And here's where it all ends.</i>
</span>
Now take a look at the output.
Here's where it all starts
I am a apple, my sequence position is 1, and my index
number is 0.
I am a banana, my sequence position is 2, and my index number is
1.
I am a orange, my sequence position is 3, and my index number is 2.
I am
a apricot, my sequence position is 4, and my index number is 3.
I am a grape,
my sequence position is 5, and my index number is 4.
And here's where it all
ends.
How does this work? Well, you may remember, from your DTML exploits, that all
sequences have built-in variables that can be used to identify the current pointer
position within the sequence. The "number" variable represents the position of
the current item in the sequence, while the "index" variable provides an alternative
zero-based indexing mechanism that serves the same purpose. And the "start" and
"end" variables provide an easy way to find out if you're at the beginning or
end of the sequence - the former is true when the current item is the first element
of the sequence and the latter is true when the current element is the last element
of the sequence.
Now, in order to access these values in your Zope Page Templates, you need to
use one or more TALES expressions. Here are the ones I've used:
repeat/fruits/start - A TALES expression for the value of the "start" variable
repeat/fruits/number - A TALES expression for the value of the "number" variable
repeat/fruits/index - A TALES expression for the value of the "index" variable
repeat/fruits/end - A TALES expression for the value of the "end" variable
You may remember, from earlier articles in this series, that every TALES path
must begin with a variable name. "repeat" is one such pre-defined variable, and
it stores information on the start and end position, number, index and length
of the sequence. This information can then be accessed using a three-part path,
such as the ones demonstrated above
The example you just saw used a simple sequence. However, you can also loop over
a collection of objects using the same technique. Take a look at a simple example
that lists the objects in the current folder.
This folder contains:
<ul>
<li tal:repeat="filelist container/objectIds">
<span
tal:replace="filelist"/>
</li>
</ul>
Here's the output:
This folder contains:
* CountingDown
Here, I've used the "container" built-in variable together with the "objectIds"
variable, which returns a sequence with the list of objects in the current folder.
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