[Zope] Difference between dtml-let & dtml-in

[Gabriel Genellina]

Hi

This piece of code works fine:

<dtml-let sql="restrictedTraverse(PathToSqlMethod)">
<dtml-in sql>
    <dtml-var AnyFieldName>,
</dtml-in>
</dtml-let>

where PathToSqlMethod is a path to any SQLMethod, and AnyFieldName is a 
column name in that SQLMethod.

Then, I didnt like the dtml-let, so I collapsed both lines, and wrote:

<dtml-in "restrictedTraverse(PathToSqlMethod)">
    <dtml-var AnyFieldName>,
</dtml-in>

and I got a KeyError in __getitem__, Error Value: 0 (zero).
After several attempts I got the right way of doing it:

<dtml-in "restrictedTraverse(PathToSqlMethod)()">
    <dtml-var AnyFieldName>,
</dtml-in>

So I need to call the SQLMethod explicitly, and then it returns a sequence 
that <dtml-in> can handle (at least, this is what I guess.)

But now, I don't understand why the ()'s arent needed using <dtml-let>, and 
then, why are them really necessary using <dtml-in "">.
I would expect both tags to behave similarly.
Perhaps someone can explain me the difference.


Gabriel Genellina
Softlab SRL