Overriding Django's {% extends %} template tag to prevent a parent template rendering in a third party app

__init__.py

"""
This needs to go somewhere that will force it to run immediately.

As the 'extends' tag always has to be first in a template, it's not
possible to use the {% load %} tag for this. Instead it must be
loaded in the same way as the django tags.

add_to_builtins function changed module in 1.7
"""
try:
    from django.template.loader import add_to_builtins
except ImportError:
    from django.template.base import add_to_builtins


add_to_builtins('my_app.templatetags.overriden_tags')

overriden_tags.py

from django import template
from django.template.loader_tags import do_extends, ExtendsNode

register = template.Library()


@register.tag('extends')
def preventable_extends(parser, token):
    node = do_extends(parser, token)
    return PreventableExtendsNode(node.nodelist, node.parent_name)


class PreventableExtendsNode(ExtendsNode):

    def render(self, context):
        prevent = context.get('prevent_extends')
        if prevent == self.parent_name.var:
            return self.nodelist.render(context)
        return super(PreventableExtendsNode, self).render(context)

view_mixin.py

class PreventExtendsMixin(object):

    def __init__(self, **kwargs):
        self.prevent_extends = kwargs.pop('prevent_extends')
        super(PreventExtendsMixin, self).__init__(**kwargs)

    def get_context_data(self, **kwargs):
        context = super(PreventExtendsMixin, self).get_context_data(**kwargs)
        context['prevent_extends'] = self.prevent_extends
        return context