enable the use string: ${foo | nothing} to avoid a KeyError

[Edwin Grubbs]

Currently, the following tal with raise a KeyError if $foo is undefined.
  <span tal:content="string: Hello, ${foo}" />

I would like to be able to indicate that I just want an empty string if the variable is undefined. The most consistent syntax would be:
  <span tal:content="string: Hello, ${foo | nothing}">

This would be a lot less redundant than what I have to do now:
  <span tal:define="foo foo | nothing" tal:content="string: Hello, ${foo}" />

[Malthe Borch (mborch)]

2009/6/30 Edwin Grubbs <email address hidden>:
> Public bug reported:
>
> Currently, the following tal with raise a KeyError if $foo is undefined.
>  <span tal:content="string: Hello, ${foo}" />
>
> I would like to be able to indicate that I just want an empty string if the variable is undefined. The most consistent syntax would be:
>  <span tal:content="string: Hello, ${foo | nothing}">

This would yield:

<span>Hello, </span>

Can't you do:

<span tal:content="string: Hello, ${foo} | string:">

\malthe

[Edwin Grubbs (edwin-grubbs)]

On Tue, Jun 30, 2009 at 5:16 PM, Malthe<email address hidden> wrote:
> 2009/6/30 Edwin Grubbs <email address hidden>:
>>  <span tal:content="string: Hello, ${foo | nothing}">
>
> This would yield:
>
> <span>Hello, </span>
>
> Can't you do:
>
> <span tal:content="string: Hello, ${foo} | string:">

I guess my example was too simple to explain the problem I am having.
Here is a better one.

<script tal:content="string: do_something('${foo}', '${bar}', '${baz}')" />

As you can see, I would have to have an alternate string for each
combination of variables that could be undefined.

-Edwin

[Malthe Borch (mborch)]

2009/7/1 Edwin Grubbs <email address hidden>:
> I guess my example was too simple to explain the problem I am having.
> Here is a better one.
>
> <script tal:content="string: do_something('${foo}', '${bar}', '${baz}')"
> />
>
> As you can see, I would have to have an alternate string for each
> combination of variables that could be undefined.

I think it's an abuse, but I see the general issue and actually I've
had this problem myself, something like:

<span tal:attributes="string:${some_class}
contenttype-${maybe_some_content_type | nothing}">...</span>

The second part should ideally be left out entirely, if not defined. Perhaps:

<span tal:attributes="string:${some_class}
${string:contenttype-${maybe_some_content_type} | nothing}">...</span>

could work?

[Edwin Grubbs (edwin-grubbs)]

On Wed, Jul 1, 2009 at 3:29 AM, Malthe<email address hidden> wrote:
> The second part should ideally be left out entirely, if not defined.
> Perhaps:
>
> <span tal:attributes="string:${some_class}
> ${string:contenttype-${maybe_some_content_type} | nothing}">...</span>
>
> could work?

I think that is a nice solution to provide full evaluation of the
expression inside of ${}.

-Edwin