"TypeError: context must be a dict rather than Context" when using loader.select_template() with Context

[Mark Jones]

The render method of the Template class looks like this

    def render(self, context=None, request=None):
        context = make_context(context, request, autoescape=self.backend.engine.autoescape)
        try:
            return self.template.render(context)
        except TemplateDoesNotExist as exc:
            reraise(exc, self.backend)

The docs show this:

>>> from django.template import Context, Template
>>> template = Template("My name is {{ my_name }}.")

>>> context = Context({"my_name": "Adrian"})
>>> template.render(context)
"My name is Adrian."

>>> context = Context({"my_name": "Dolores"})
>>> template.render(context)
"My name is Dolores."

However make_context looks like this (and throws an exception because of it):

    if context is not None and not isinstance(context, dict):
        raise TypeError('context must be a dict rather than %s.' % context.__class__.__name__)
    if request is None:
        context = Context(context, **kwargs)
    else:
        # The following pattern is required to ensure values from
        # context override those from template context processors.
        original_context = context
        context = RequestContext(request, **kwargs)
        if original_context:
            context.push(original_context)
    return context

I think it needs this code placed before the original code in make_context

    if isinstance(context, Context):
        return context

so that if an actual context is passed in, it works as documented.

This bug only comes about when you select a template using code that looks like this:

from django.template import loader, Context
            servertemplate = loader.select_template(["deployment/%s" % options['webserver'],
                                                     "deployment/default_%s" % options['webserver']])

because the loader returns an instance of <class 'django.template.backends.django.Template'> instead of <class 'django.template.base.Template'> which has a different render method that causes this problem.

My change does fix the issue, but I'm not sure if this is the right fix, or if there should be another.

[Tim Graham]

To fix your code, you should indeed call render() with a plaint dict rather than a Context.

This is related to ​a change in Django 1.11 (#27258). Does some documentation need clarification?

[Tim Graham]

I see you moved the conversation to ticket:27258#comment:12 and 13. Another possibility to fix your code would be to adapt the approach from #27722 like this:

servertemplate = loader.select_template(...).template

This won't work if you use any template engine besides the DjangoTemplates but your comment suggests you don't care about that.

If you have some other suggestion of a code or documentation change to make, feel free to reopen the ticket.