Django: logging template errors

Question

When I make an error in a django template {{placeholder}}, I get no error, just blank space in the output where I was expecting content. Is there a way to see something in my logs when this occurs, preferably using logging.warning or logging.error?

Portauprince

Answer 1

The only thing Django provides for handling unknown context variables in TEMPLATE_STRING_IF_INVALID. You're going to have to do some deeper hacking of the template engine if you want better than that.

Yoshikoyoshio

Ignacio, with the new versions of Django, is that still the only way to go? Thanks – Delectate

django.template logger was intoduced in Django 1.9 docs.djangoproject.com/ja/1.9/topics/logging/#django-template – Frugivorous

Answer 2

Yes, there is. Just add in your development settings.py:

LOGGING = {
    'version': 1,
    'disable_existing_loggers': False,
    'handlers': {
        'console': {
            'class': 'logging.StreamHandler',
        },
    },
    'loggers': {
        'django.template': {
            'handlers': ['console'],
            'level': os.getenv('DJANGO_LOG_LEVEL', 'DEBUG'),
        },
    },
}

As roboslone stated, Django 1.9 did introduce it. The snippet is very similar to the second of Configuring logging examples in Django docs.

Biogen

Answer 3

In Django >= 1.8, TEMPLATE_STRING_IF_INVALID has been deprecated in favor of string_if_invalid in settings.TEMPLATES.

If you want to do a little more than depend on DEBUG messages from the django.template logger, you can fool the following code in django.template.base.FilterExpression.render():

if '%s' in string_if_invalid:
    return string_if_invalid % self.var

With a class like the following:

class InvalidString(object):
    def __mod__(self, other):
        log.error('Missing template variable: "%s"', other)
        # ... do other interesting things ... 
        return u''

    def __contains__(self, item):
        return item == '%s'

And set string_if_invalid in settings.TEMPLATES:

TEMPLATES = [{
    'OPTIONS': {'string_if_invalid': InvalidString()}
    # ...
}]

Frangible