[ZPT] how do I test the existence of a variable?

[Harry Wilkinson]

> <span define="foo python:1">
>      <b tal:define="bar template/foo | default"
>         tal:content="bar">Foo</b>
> </span>
>
> close but no cigar: the above displays the default value.  The variable
> 'foo' has not been pushed onto the 'template' namespace.
>
> incidentally, the reason I need to do this is because I'm trying to
> parameterise my macros, thus:
>
> 1. Macro definition:
>
> <p metal:define-macro="foo"
>    tal:define="bar mynamespace/bar | python:[]">
>  <span tal:repeat="item bar">
>    stuff
>  </span>
> </p>
>
>
> 2: Using it with a parameter:
>
> <div tal:define="bar python:['a','b','c']">
>  <p metal:use-macro="foo">
>    My macro goes here
>  </p>
> </div>

Maybe I've missed the point but this seems simple enough to me.  I've written 
macros the way I think you're describing before just like this:

1. Macro definition:

<p metal:define-macro="foo"
   tal:define="rhubarb bar | python:[]">
 <span tal:repeat="item rhubarb">
   stuff
 </span>
</p>

'bar' just gets plucked out the current namespace.  Or maybe I've missed some 
deep and complicated problem here : )


Harry