id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
26603	Can't use lazy objects as template names with cached loader anymore	Sylvain Fankhauser	Simon Charette	"It looks like commit https://github.com/django/django/commit/bd145e7209a0e628cced10384bd6f62d65c0f211 introduced a regression in Django 1.9.6. Before this commit, you could pass a lazy object to the {% extends %} tag and it would work just fine, however with Django 1.9.6 the following exception is raised:

{{{
Template error:
In template /home/vagrant/ENV/local/lib/python2.7/site-packages/parler/templates/admin/parler/change_form.html, error at line 1
   sequence item 0: expected string, __proxy__ found   1 :  {% extends default_change_form_template|default:""admin/change_form.html"" %} 
   2 : 
   3 : {% block field_sets %}
   4 : {% if language_tabs %}{% include ""admin/parler/language_tabs.html"" %}{% endif %}
   5 : {{ block.super }}
   6 : {% endblock %}
   7 : 

Traceback:

File ""/home/vagrant/ENV/local/lib/python2.7/site-packages/django/core/handlers/base.py"" in get_response
  174.                     response = self.process_exception_by_middleware(e, request)

File ""/home/vagrant/ENV/local/lib/python2.7/site-packages/django/core/handlers/base.py"" in get_response
  172.                     response = response.render()

File ""/home/vagrant/ENV/local/lib/python2.7/site-packages/django/template/response.py"" in render
  160.             self.content = self.rendered_content

File ""/home/vagrant/ENV/local/lib/python2.7/site-packages/django/template/response.py"" in rendered_content
  137.         content = template.render(context, self._request)

File ""/home/vagrant/ENV/local/lib/python2.7/site-packages/django/template/backends/django.py"" in render
  95.             return self.template.render(context)

File ""/home/vagrant/ENV/local/lib/python2.7/site-packages/django/template/base.py"" in render
  206.                     return self._render(context)

File ""/home/vagrant/ENV/local/lib/python2.7/site-packages/django/test/utils.py"" in instrumented_test_render
  92.     return self.nodelist.render(context)

File ""/home/vagrant/ENV/local/lib/python2.7/site-packages/django/template/base.py"" in render
  992.                 bit = node.render_annotated(context)

File ""/home/vagrant/ENV/local/lib/python2.7/site-packages/django/template/base.py"" in render_annotated
  959.             return self.render(context)

File ""/home/vagrant/ENV/local/lib/python2.7/site-packages/django/template/loader_tags.py"" in render
  151.         compiled_parent = self.get_parent(context)

File ""/home/vagrant/ENV/local/lib/python2.7/site-packages/django/template/loader_tags.py"" in get_parent
  148.         return self.find_template(parent, context)

File ""/home/vagrant/ENV/local/lib/python2.7/site-packages/django/template/loader_tags.py"" in find_template
  128.             template_name, skip=history,

File ""/home/vagrant/ENV/local/lib/python2.7/site-packages/django/template/engine.py"" in find_template
  157.                         name, template_dirs=dirs, skip=skip,

File ""/home/vagrant/ENV/local/lib/python2.7/site-packages/django/template/loaders/cached.py"" in get_template
  49.         key = self.cache_key(template_name, template_dirs, skip)

File ""/home/vagrant/ENV/local/lib/python2.7/site-packages/django/template/loaders/cached.py"" in cache_key
  103.         return '-'.join(filter(bool, [template_name, skip_prefix, dirs_prefix]))

Exception Type: TypeError at /en/admin/aldryn_newsblog/newsblogconfig/1/change/
Exception Value: sequence item 0: expected string, __proxy__ found
}}}

You can easily reproduce the problem in a new project by using the following code in the urls.py file:

{{{
#!python
from django.views.generic import TemplateView
from django.utils.functional import lazy


class TestView(TemplateView):
    template_name = 'home.html'

    def get_context_data(self, **kwargs):
        context = super(TestView, self).get_context_data(**kwargs)
        context['extended_template'] = lazy(lambda: 'base.html')
        return context

urlpatterns = [
    url(r'^$', TestView.as_view()),
]
}}}

And create a file templates/home.html (and adapt the template dirs accordingly):

{{{
{% extends extended_template %}
}}}

The bug is present on master as well."	Bug	closed	Template system	1.9	Release blocker	fixed			Ready for checkin	1	0	0	0	0	0