Make Django templates fail fast on a variety of errors.

It's happened to all of us. We forget a template variable in a context, or have a bug in a property accessed in a template. Django, a battle-forged web framework, was designed to serve the damn webpage no matter what, much to the chagrin of web developers who have found easily fixable bugs going unfixed for months. It's the worst. It's literally like getting stabbed in the back and left to bleed out, muttering "Et tu, Django?" with your last breaths. Literally. It's that bad.

Enter django-pedant, the pedantic template renderer's friend.

I think you mean "about what is this package pedantic?" Seriously, though, Django is very lenient in at least the following ways:

• Exceptions raised in computing {% if expression %} expressions other builtin tags. In general, errors in custom tags are allowed to propagate.
• KeyError and AttributeError in {{ context_variable }} expressions.
• UnicodeDecodeError is caught in some places and replaced with '' (TODO)
• In evaluating {{ expr|filter }} expressions, FilterExpression.resolve has ignore_failures=True in some case, which swallows VariableDoesNotExist errors.

To decorate your view which might hide template failures, simply do:

from pedant.decorators import fail_on_template_errors

@fail_on_template_errors
def my_view(request):
    # [...]
    return render_to_string('foo.html')

If there are errors in foo.html, the view will now raise a PedanticTemplateRenderingError if there were any errors in rendering the template that Django swallows.

To simply log if there are template failures, you can use the log_on_template_errors decorator:

import logging

from pedant.decorators import log_on_template_errors

logger = logging.getLogger('myapp.views')

@log_on_template_errors(logger, log_level=logging.INFO)
def my_view(request):
    # [...]
    return render_to_string('foo.html')

This will log template errors to the myapp.views logger at INFO. The default log level is logging.ERROR.

For using pedantic rendering in your view tests, you can simply inherit from PedanticTestCase:

from django.template import Template, Context
from pedant.utils import PedanticTestCase

class TestBuggyTemplate(PedanticTestCase):
    def test(self):
        Template('{{ foo }}').render(Context({'bar': 'baz'}))

That test will fail since foo is undefined in the template. PedanticTestCase inherits from the standard Django TestCase. PedanticTestCaseMixin is also provided if you don't want to incur the transactional overhead of Django's test case (e.g. for unit tests).

NOSE_COVER_MIN_PERCENTAGE=100 django-admin.py test \
    --with-xunit --with-doctest --settings=settings_test \
    --with-coverage --cover-package=pedant --cover-html