Django template context variable injector decorator (inject variables into templates based on URL, not view)

template_injector.py

#from django.core.urlresolvers import reverse, reverse_lazy, NoReverseMatch
# from django.utils.functional import lazy


# CONTEXT_INJECTOR_REVERSE_DEBUG = getattr(settings, 'CONTEXT_INJECTOR_REVERSE_DEBUG', False)


class TemplateContextInjectorMiddleware(object):
    lazy_url_func_pairs = []

    @classmethod
    def add_func_pair(cls, key, func):
        cls.lazy_url_func_pairs.append((key, func))

    def get_context_processors(self, path):
        """
        Gets a list of context processors associated with this path. 
        Evaluates lazy calls upon first call (reverse must be evaluated after django fully initializes)
        """
        if not hasattr(self, '_url_func_pairs'):
            self._url_func_pairs = {}
            for proxy, func in self.lazy_url_func_pairs:
                self._url_func_pairs.setdefault(unicode(proxy), []).append(func)
        return self._url_func_pairs.get(path)

    def process_template_response(self, request, response):
        context_processors = self.get_context_processors(request.path)

        if context_processors:
            for function in context_processors:
                new_context = function(request)

                print 'Function found... injecting context', new_context
                response.context_data.update(new_context)
        return response


def inject_variables(url=None, reverse=None, args=None, kwargs=None):
    """
    Inject variables into template response


    @inject_variables(reverse_lazy('products:list', kwargs={'product_type_slug': 'ipad-case'}))
    def foo(request):
        return {
            'products': [],
        }
    """
    if url and not isinstance(url, basestring):
        raise Exception("First argument or url keyword must be a string (a url path)")

    if not url and not reverse:
        raise Exception("Must supply url or reverse keyword argument")

    # this must RETURN a decorator.
    def decorator_function(func):
        TemplateContextInjectorMiddleware.add_func_pair(url or reverse, func)
        def wrapped(*func_args, **func_kwargs):
            return func(*func_args, **func_kwargs)
        return wrapped

    return decorator_function