# Wrapper for loading templates from storage of some sort (e.g. filesystem, database).
#
# This uses the TEMPLATE_LOADERS setting, which is a list of loaders to use.
# Each loader is expected to have this interface:
#
# callable(name, dirs=[])
#
# name is the template name.
# dirs is an optional list of directories to search instead of TEMPLATE_DIRS.
#
# The loader should return a tuple of (template_source, path). The path returned
# might be shown to the user for debugging purposes, so it should identify where
# the template was loaded from.
#
# A loader may return an already-compiled template instead of the actual
# template source. In that case the path returned should be None, since the
# path information is associated with the template during the compilation,
# which has already been done.
#
# Each loader should have an "is_usable" attribute set. This is a boolean that
# specifies whether the loader can be used in this Python installation. Each
# loader is responsible for setting this when it's initialized.
#
# For example, the eggs loader (which is capable of loading templates from
# Python eggs) sets is_usable to False if the "pkg_resources" module isn't
# installed, because pkg_resources is necessary to read eggs.
from django.core.exceptions import ImproperlyConfigured
from django.template.base import Origin, Template, Context, TemplateDoesNotExist
from django.conf import settings
from django.utils.module_loading import import_string
from django.utils import six
template_source_loaders = None
class BaseLoader(object):
is_usable = False
def __init__(self, *args, **kwargs):
pass
def __call__(self, template_name, template_dirs=None):
return self.load_template(template_name, template_dirs)
def load_template(self, template_name, template_dirs=None):
source, display_name = self.load_template_source(template_name, template_dirs)
origin = make_origin(display_name, self.load_template_source, template_name, template_dirs)
try:
template = get_template_from_string(source, origin, template_name)
return template, None
except TemplateDoesNotExist:
# If compiling the template we found raises TemplateDoesNotExist, back off to
# returning the source and display name for the template we were asked to load.
# This allows for correct identification (later) of the actual template that does
# not exist.
return source, display_name
def load_template_source(self, template_name, template_dirs=None):
"""
Returns a tuple containing the source and origin for the given template
name.
"""
raise NotImplementedError('subclasses of BaseLoader must provide a load_template_source() method')
def reset(self):
"""
Resets any state maintained by the loader instance (e.g., cached
templates or cached loader modules).
"""
pass
class LoaderOrigin(Origin):
def __init__(self, display_name, loader, name, dirs):
super(LoaderOrigin, self).__init__(display_name)
self.loader, self.loadname, self.dirs = loader, name, dirs
def reload(self):
return self.loader(self.loadname, self.dirs)[0]
def make_origin(display_name, loader, name, dirs):
if settings.TEMPLATE_DEBUG and display_name:
return LoaderOrigin(display_name, loader, name, dirs)
else:
return None
def find_template_loader(loader):
if isinstance(loader, (tuple, list)):
loader, args = loader[0], loader[1:]
else:
args = []
if isinstance(loader, six.string_types):
TemplateLoader = import_string(loader)
if hasattr(TemplateLoader, 'load_template_source'):
func = TemplateLoader(*args)
else:
# Try loading module the old way - string is full path to callable
if args:
raise ImproperlyConfigured("Error importing template source loader %s - can't pass arguments to function-based loader." % loader)
func = TemplateLoader
if not func.is_usable:
import warnings
warnings.warn("Your TEMPLATE_LOADERS setting includes %r, but your Python installation doesn't support that type of template loading. Consider removing that line from TEMPLATE_LOADERS." % loader)
return None
else:
return func
else:
raise ImproperlyConfigured('Loader does not define a "load_template" callable template source loader')
def find_template(name, dirs=None):
# Calculate template_source_loaders the first time the function is executed
# because putting this logic in the module-level namespace may cause
# circular import errors. See Django ticket #1292.
global template_source_loaders
if template_source_loaders is None:
loaders = []
for loader_name in settings.TEMPLATE_LOADERS:
loader = find_template_loader(loader_name)
if loader is not None:
loaders.append(loader)
template_source_loaders = tuple(loaders)
for loader in template_source_loaders:
try:
source, display_name = loader(name, dirs)
return (source, make_origin(display_name, loader, name, dirs))
except TemplateDoesNotExist:
pass
raise TemplateDoesNotExist(name)
[docs]def get_template(template_name, dirs=None):
"""
Returns a compiled Template object for the given template name,
handling template inheritance recursively.
"""
template, origin = find_template(template_name, dirs)
if not hasattr(template, 'render'):
# template needs to be compiled
template = get_template_from_string(template, origin, template_name)
return template
def get_template_from_string(source, origin=None, name=None):
"""
Returns a compiled Template object for the given template code,
handling template inheritance recursively.
"""
return Template(source, origin, name)
def render_to_string(template_name, dictionary=None, context_instance=None,
dirs=None):
"""
Loads the given template_name and renders it with the given dictionary as
context. The template_name may be a string to load a single template using
get_template, or it may be a tuple to use select_template to find one of
the templates in the list. Returns a string.
"""
if isinstance(template_name, (list, tuple)):
t = select_template(template_name, dirs)
else:
t = get_template(template_name, dirs)
if not context_instance:
return t.render(Context(dictionary))
if not dictionary:
return t.render(context_instance)
# Add the dictionary to the context stack, ensuring it gets removed again
# to keep the context_instance in the same state it started in.
with context_instance.push(dictionary):
return t.render(context_instance)
[docs]def select_template(template_name_list, dirs=None):
"Given a list of template names, returns the first that can be loaded."
if not template_name_list:
raise TemplateDoesNotExist("No template names provided")
not_found = []
for template_name in template_name_list:
try:
return get_template(template_name, dirs)
except TemplateDoesNotExist as e:
if e.args[0] not in not_found:
not_found.append(e.args[0])
continue
# If we get here, none of the templates could be loaded
raise TemplateDoesNotExist(', '.join(not_found))
Feb 24, 2017