making django templates "strict"?

[Webb S.]

Is there a way (in Linux) to make the rendering of Django templates
error out when a object property is undefined?

So that <p>blah {{ bldg.name }} </p> throws a big fat stack trace,
rather than rendering to <p> blah </p>

This is mostly a problem for me with generated javascript code which
is building a map. I am sure there is a better way for that, but I
haven't found it yet, and I would prefer to render templates strictly
anyway.

Tx!

[Niklasro(.appspot)]

Answer is yes just test if (not) None or likewise just that doing with
no none and no null tests getting it farther than obvious.

[Webb S.]

On Jul 11, 4:57 am, "Niklasro(.appspot)" <nikla...@gmail.com> wrote:
> Answer is yes just test if (not) None or likewise just that doing with
> no none and no null tests getting it farther than obvious.

Yeah, I realize I could add code to test for empty variables. I was
hoping for a setting that would automatically do that, like "use
strict" in Perl.

[djidjadji]

In the django.template module:
The problem is with the FilterExpression.resolve() method.
It handles the ignore_failures case wrong.
And the VariableNode.render() should call
FilterExpression.resolve(context,True).
The default behavior is to ignore the failures.

I have found two solutions
################################
Method 1:
Write a custom template filter that calls resolve_variable, and thus
raise an exception if {{var.arg}} fails. This will not catch the case
where var is not part of the template context {{var}}

The filter function is
-----------------------------
register = webapp.template.create_template_register()

@register.filter
def resolve(value, arg):
"""resolve the lookup of arg in value, raise exception if not found"""
return resolve_variable('var.' + arg, {'var' : value})
-----------------------------

In the template use, instead of {{var.arg}}
{{var|resolve:"arg"}}

################################
Method 2:
Monkey patch the FilterExpression.resolve() method. Replace it with a
working version.
Add the following code to your request handler .py file

-----------------------------
from google.appengine.ext.webapp import template
import django.template
from django.template import resolve_variable,VariableDoesNotExist
from django.conf import settings

##class FilterExpression(object):
## from django.template
def resolve(self, context, ignore_failures=False):
try:
obj = resolve_variable(self.var, context)
except VariableDoesNotExist:
if ignore_failures:
if settings.TEMPLATE_STRING_IF_INVALID:
return settings.TEMPLATE_STRING_IF_INVALID
else:
obj = settings.TEMPLATE_STRING_IF_INVALID
else:
# simplify the stackdump
if isinstance(e.params[1],django.template.context.Context):
raise VariableDoesNotExist(e.msg,(e.params[0],"Main context"))
raise
for func, args in self.filters:
arg_vals = []
for lookup, arg in args:
if not lookup:
arg_vals.append(arg)
else:
arg_vals.append(resolve_variable(arg, context))
obj = func(obj, *arg_vals)
return obj

django.template.FilterExpression.resolve = resolve
-----------------------------
In the template: {{var.notthere}} will raise an exception, with only
"var" in the context.
And {{notthere}} will print an exception without context dump.

2010/7/11 Webb S. <webb.s...@gmail.com>:

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