import functools
from collections import Counter, OrderedDict
from pathlib import Path
from django.apps import apps
from django.conf import settings
from django.core.exceptions import ImproperlyConfigured
from django.utils.functional import cached_property
from django.utils.module_loading import import_string
class InvalidTemplateEngineError(ImproperlyConfigured):
pass
class EngineHandler:
def __init__(self, templates=None):
"""
templates is an optional list of template engine definitions
(structured like settings.TEMPLATES).
"""
self._templates = templates
self._engines = {}
@cached_property
def templates(self):
if self._templates is None:
self._templates = settings.TEMPLATES
templates = OrderedDict()
backend_names = []
for tpl in self._templates:
try:
# This will raise an exception if 'BACKEND' doesn't exist or
# isn't a string containing at least one dot.
default_name = tpl['BACKEND'].rsplit('.', 2)[-2]
except Exception:
invalid_backend = tpl.get('BACKEND', '<not defined>')
raise ImproperlyConfigured(
"Invalid BACKEND for a template engine: {}. Check "
"your TEMPLATES setting.".format(invalid_backend))
tpl = {
'NAME': default_name,
'DIRS': [],
'APP_DIRS': False,
'OPTIONS': {},
**tpl,
}
templates[tpl['NAME']] = tpl
backend_names.append(tpl['NAME'])
counts = Counter(backend_names)
duplicates = [alias for alias, count in counts.most_common() if count > 1]
if duplicates:
raise ImproperlyConfigured(
"Template engine aliases aren't unique, duplicates: {}. "
"Set a unique NAME for each engine in settings.TEMPLATES."
.format(", ".join(duplicates)))
return templates
def __getitem__(self, alias):
try:
return self._engines[alias]
except KeyError:
try:
params = self.templates[alias]
except KeyError:
raise InvalidTemplateEngineError(
"Could not find config for '{}' "
"in settings.TEMPLATES".format(alias))
# If importing or initializing the backend raises an exception,
# self._engines[alias] isn't set and this code may get executed
# again, so we must preserve the original params. See #24265.
params = params.copy()
backend = params.pop('BACKEND')
engine_cls = import_string(backend)
engine = engine_cls(params)
self._engines[alias] = engine
return engine
def __iter__(self):
return iter(self.templates)
def all(self):
return [self[alias] for alias in self]
@functools.lru_cache()
def get_app_template_dirs(dirname):
"""
Return an iterable of paths of directories to load app templates from.
dirname is the name of the subdirectory containing templates inside
installed applications.
"""
template_dirs = [
str(Path(app_config.path) / dirname)
for app_config in apps.get_app_configs()
if app_config.path and (Path(app_config.path) / dirname).is_dir()
]
# Immutable return value because it will be cached and shared by callers.
return tuple(template_dirs)
