Make django templates strict

问题

In a django template, a call to {{ var }} will silently fail if var is undefined. That makes templates hard to debug. Is there a setting I can switch so django will throw an exception in this case?

The only hint at a solution I've found online is http://groups.google.com/group/google-appengine/browse_thread/thread/86a5b12ff868038d and that sounds awfully hacky.

回答1:

Django<=1.9

Set TEMPLATE_STRING_IF_INVALID = 'DEBUG WARNING: undefined template variable [%s] not found' in your settings.py.

See docs:
https://docs.djangoproject.com/en/1.9/ref/settings/#template-string-if-invalid

Django>=1.10

Set string_if_invalid = 'DEBUG WARNING: undefined template variable [%s] not found' template option in your settings.py.

See docs: https://docs.djangoproject.com/en/2.0/topics/templates/#module-django.template.backends.django

Also read: http://docs.djangoproject.com/en/dev/ref/templates/api/#invalid-template-variables

回答2:

This hack from djangosnippets will raise an exception when an undefined variable is encountered in a template.

# settings.py
class InvalidVarException(object):
    def __mod__(self, missing):
        try:
            missing_str = unicode(missing)
        except:
            missing_str = 'Failed to create string representation'
        raise Exception('Unknown template variable %r %s' % (missing, missing_str))
    def __contains__(self, search):
        if search == '%s':
            return True
        return False

TEMPLATE_DEBUG = True
TEMPLATE_STRING_IF_INVALID = InvalidVarException()

回答3:

That's part of the design. It allows you to provide defaults and switch based on whether or not a variable exists in the context. It also allows templates to be very flexible and promotes re-usability of templates instead of a strict "each view must have it's own template" approach.

More to the point, templates are not really supposed to be "debugged". The idea is to put as much of your logic as possible outside the template, in the views or models. If you want to figure out why a variable that's supposed to be passed to the context isn't, the place to debug that is in your view. Just drop import pdb;pdb.set_trace() somewhere before your view returns and poke around.

来源：https://stackoverflow.com/questions/8990224/make-django-templates-strict