[stringtemplate-interest] Problem in multivalued attribute handling?

[Terence Parr]

On Jul 11, 2006, at 9:24 AM, Colin Bean wrote:

> Okay, I've got the beginnings of a fix.  The problem is indeed in
> checking for the existence of an attribute.  As Praki mentioned
> earlier, using a conditional like "if x:" looks like it should simply
> check for the existence of x, but in fact evaluates to false not only
> if x is None, but also if x is an empty container or a numeric zero.

Empty container is correct, but 0 is incorrect ;)

> It's a weird little python feature that has bitten me a couple of
> times; the solution is to explicitly check if a value is None.
> I'm sure that there are many other places in the code that could use a
> review for this, the following changes made PyST correctly evaluate a
> (single or multi-valued) attribute with the integer value of zero.  I
> changed one line in StringTemplate.py, where it checks for the
> attribute's existence before setting it, and one in
> language/ASTExpr.py, where it again checks existence before writing an
> attribute out.  I ran the code through the unit tests and it was fine,
> but other than that and my "zero" test I haven't run this code
> anywhere else -- ymmv.  Here's a diff of the changes:

Sweet!  Thanks, Colin :)  I'm CC'ing Marq in case he misses this.

Ter
> --- StringTemplateOrig.py       2006-07-10 15:53:44.000000000 -0700
> +++ StringTemplate.py   2006-07-10 15:59:49.000000000 -0700
> @@ -677,7 +677,7 @@
>             # a normal call to setAttribute with unknown attribute
>             raise KeyError("no such attribute: " + name +
>                " in template context " +
> self.getEnclosingInstanceStackString())
> -        if value:
> +        if value is not None:
>             attributes[name] = value
>         elif isinstance(value, list) or \
>              isinstance(value, dict) or \
> --- language/ASTExprOrig.py     2006-07-10 15:57:35.000000000 -0700
> +++ language/ASTExpr.py 2006-07-10 15:11:35.000000000 -0700
> @@ -390,7 +390,7 @@
>         return self._write(this, o, out, separator)
>
>     def _write(self, this, o, out, separator):
> -        if not o:
> +        if o is None:
>             return 0
>         n = 0
>         try:
>
>
> If I find anything else relevant to this I'll post it.
> Regards,
> -Colin
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