Django: The perils of string_if_invalid in templates

Django’s template engine has a string_if_invalid option that replaces missing variable lookups with a string of your choice:

TEMPLATES = [
    {
        "BACKEND": "django.template.backends.django.DjangoTemplates",
        # ...
        "OPTIONS": {
            # ...
            "string_if_invalid": "MISSING VARIABLE %s",
        },
    }
]

The %s will be replaced with the name of the missing variable.

This exists as a debugging aid to …