Wrapper for loading templates from "templates" directories in the specified apps.

loaders.py

"""
Wrapper for loading templates from "templates" directories in the specified
apps.

>>> {% extends 'grappelli,admin:admin/change_list.html' %}
"""

import os
import sys

from django.apps import apps
from django.template.loaders import app_directories
from django.utils._os import safe_join
from django.utils import six


app_template_dirs_cache = {}


def get_app_template_dir(app_label):
    if app_label not in app_template_dirs_cache:
        app_template_dirs = []
        app_config = apps.get_app_config(app_label)
        if app_config.path:
            template_dir = os.path.join(app_config.path, 'templates')
            if os.path.isdir(template_dir):
                if six.PY2:
                    fs_encoding = sys.getfilesystemencoding() or \
                                  sys.getdefaultencoding()
                    template_dir = template_dir.decode(fs_encoding)
                app_template_dirs.append(template_dir)
        app_template_dirs_cache[app_label] = tuple(app_template_dirs)
    return app_template_dirs_cache[app_label]


class Loader(app_directories.Loader):

    is_usable = True

    def get_template_sources(self, template_name, template_dirs=None):
        """
        Returns the absolute paths to "template_name", when appended to each
        directory in "template_dirs". Any paths that don't lie inside one of the
        template dirs are excluded from the result set, for security reasons.
        """
        if ':' in template_name:
            app_labels, template_name = template_name.split(':')
            for app_label in app_labels.split(','):
                for template_dir in get_app_template_dir(app_label):
                    try:
                        yield safe_join(template_dir, template_name)
                    except UnicodeDecodeError:
                        # The template dir name was a bytestring that wasn't
                        # valid UTF-8.
                        raise
                    except ValueError:
                        # The joined path was located outside of template_dir.
                        pass