[Zope] TAL: test() or condition Howto?

[Ivo van der Wijk]

On Fri, Jan 31, 2003 at 12:12:55PM +0100, Elena Schulz wrote:
> Hi,
> 
> I have the followong TAL-expression:
> 
>     <td
>     tal:content="structure python:here.test(myImportantCondition and
> myExpensiveMethod(), myExpensiveMethod(),
> 'myDefaultString')">myDefaultString</td>
> 
> To execute 'myExpensiveMethod()' 'myImportantCondition' must be 'true'. But
> I want to avoid to execute 'myExpensiveMethod()' two times. How can I achive
> that? As default-value myDefaultString should be served.
> 

I've given this some thought, and it's actually rather difficult (if you
want to invoke myExpensiveMethod() just once and only if myImportantCondition
is true).

Also most people don't seem to realize that test() doesn't do lazy evaluation -
the ZPT above will *always* invoke at least once, no matter what 
myImportantCondition is.

My advice would be to use a pythonscript.

Cheers

	Ivo

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