Bug in ability to use render_to_string()

[peterbe]

This works in regular django:

from django.test import TestCase
from django.template.loader import render_to_string
from django.template import Context


class SimpleTest(TestCase):

    def test_render_to_string(self):

        context = {'name': 'Peter'}
        html = render_to_string('homepage/test.html', context)
        assert 'Name:Peter' in html

        ccontext = Context(context)
        html = render_to_string('homepage/test.html', ccontext)
        assert 'Name:Peter' in html

But if fails when using jingo. It fails when the context parameter is a real subclass of the Context class.
The documentation says you're supposed to be able to pass either a dict or a Context instance.
https://docs.djangoproject.com/en/dev/ref/templates/api/#the-render-to-string-shortcut

The traceback is this:

Traceback (most recent call last):
  File "/Users/peterbe/dev/DJANGO/django-peterbecom/apps/homepage/tests.py", line 15, in test_render_to_string
    html = render_to_string('homepage/test.html', ccontext)
  File "/Users/peterbe/virtualenvs/peterbecom2/lib/python2.7/site-packages/django/template/loader.py", line 171, in render_to_string
    return t.render(Context(dictionary))
  File "/Users/peterbe/virtualenvs/peterbecom2/lib/python2.7/site-packages/jingo/__init__.py", line 172, in render
    context_dict.update(d)
ValueError: dictionary update sequence element #0 has length 1; 2 is required

The relevant code is this:

class Template(jinja2.Template):

    def render(self, context={}):
        """Render's a template, context can be a Django Context or a
        dictionary.
        """
        # flatten the Django Context into a single dictionary.
        context_dict = {}
        if hasattr(context, 'dicts'):
            for d in context.dicts:
                context_dict.update(d)
        else:
            context_dict = context
        ...

[peterbe]

Crap! I misinterpreted the documentation. If you're not going to send a simple dict you use the context_instance like this:

ccontext = Context(context)
html = render_to_string('homepage/test.html', context_instance=ccontext)

The original reason for investigating this is probably where the fault is at.