Template name overlays for Django

debug_loader.py

from django.template.loader import BaseLoader
from django.template.loader import find_template_loader
from django.template.loader import make_origin
from django.template.base import TemplateDoesNotExist
from django.template.base import Template


'''
Deubug template loader visually shows which templates are being invoked in the
process of rendering an entire page. To use, wrap your your existing loaders
tuple with DebugLoader instead of CachedLoader, e.g.:


TEMPLATE_LOADERS = (
    ('cir.base.debug_loader.DebugLoader', (
        'django.template.loaders.filesystem.Loader',
        'django.template.loaders.app_directories.Loader',
        'dbtemplates.loader.Loader',
    )),
)

Bulk of this solution is by Stephan on S.O.:
http://stackoverflow.com/questions/21766176/django-display-template-paths-as-overlay
'''


class DebugLoader(BaseLoader):
    is_usable = True

    def __init__(self, loaders):
        self._loaders = loaders
        self._cached_loaders = []

    @property
    def loaders(self):
        # Resolve loaders on demand to avoid circular imports
        if not self._cached_loaders:
                # Set self._cached_loaders atomically. Otherwise, another thread
                # could see an incomplete list. See #17303.
                cached_loaders = []
                for loader in self._loaders:
                    cached_loaders.append(find_template_loader(loader))
                self._cached_loaders = cached_loaders
        return self._cached_loaders

    def load_template(self, template_name, template_dirs=None):
        source = None

        for loader in self.loaders:
            try:
                source, display_name = loader.load_template_source(template_name, template_dirs)
            except TemplateDoesNotExist:
                pass
            else:
                break

        if not source:
            raise TemplateDoesNotExist

        origin = make_origin(display_name, loader.load_template_source, template_name, template_dirs)

        try:
            template = self.get_template_from_string(source, origin, template_name)
            return template, None
        except TemplateDoesNotExist:
            return source, display_name

    def get_template_from_string(self, source, origin, template_name):
        open_string = '<div style="font-size:10px; border: 1px solid #bfbfbf;">'
        close_string = '</div>'

        source = source + open_string + template_name + close_string
        return Template(source, origin, template_name)