Show undefined variable errors in Django templates?

Question

How can I ask Django to tell me when it encounters, for example, an undefined variable error while it\'s rendering templates?

I\'ve tried the obvious DEBUG = T

Answer 1

Put this in your debug settings:

class InvalidString(str):
    def __mod__(self, other):
        from django.template.base import TemplateSyntaxError
        raise TemplateSyntaxError(
            "Undefined variable or unknown value for: \"%s\"" % other)

TEMPLATE_STRING_IF_INVALID = InvalidString("%s")

This should raise an error when the template engine sees or finds an undefined value.

Answer 2

I believe that's a major oversight on Django's part and the primary reason I prefer not to use their default template engine. The sad truth is that, at least for now (Django 1.9), you can't achieve this effect reliably.

• You can make Django raise an exception when {{ undefined_variable }} is encountered - by using "the hack" described in slacy's answer.

• You can't make Django raise the same exception on {% if undefined_variable %} or {% for x in undefined_variable %} etc. "The hack" doesn't work in such cases.

• Even in cases in which you can, it is strongly discouraged by Django authors to use this technique in production environment. Unless you're sure you don't use Django's built-in templates in your app, you should use "the hack" only in DEBUG mode.

However, if you're stuck with Django's templates for now, I would recommend to use slacy's answer, just make sure you're in DEBUG mode.