django/django/template/engine.py

from django.core.exceptions import ImproperlyConfigured
from django.utils import lru_cache, six
from django.utils.functional import cached_property
from django.utils.module_loading import import_string

from .base import Context, Template
from .context import _builtin_context_processors
from .exceptions import TemplateDoesNotExist
from .library import import_library


class Engine(object):
    default_builtins = [
        'django.template.defaulttags',
        'django.template.defaultfilters',
        'django.template.loader_tags',
    ]

    def __init__(self, dirs=None, app_dirs=False, context_processors=None,
                 debug=False, loaders=None, string_if_invalid='',
                 file_charset='utf-8', libraries=None, builtins=None, autoescape=True):
        if dirs is None:
            dirs = []
        if context_processors is None:
            context_processors = []
        if loaders is None:
            loaders = ['django.template.loaders.filesystem.Loader']
            if app_dirs:
                loaders += ['django.template.loaders.app_directories.Loader']
            if not debug:
                loaders = [('django.template.loaders.cached.Loader', loaders)]
        else:
            if app_dirs:
                raise ImproperlyConfigured(
                    "app_dirs must not be set when loaders is defined.")
        if libraries is None:
            libraries = {}
        if builtins is None:
            builtins = []

        self.dirs = dirs
        self.app_dirs = app_dirs
        self.autoescape = autoescape
        self.context_processors = context_processors
        self.debug = debug
        self.loaders = loaders
        self.string_if_invalid = string_if_invalid
        self.file_charset = file_charset
        self.libraries = libraries
        self.template_libraries = self.get_template_libraries(libraries)
        self.builtins = self.default_builtins + builtins
        self.template_builtins = self.get_template_builtins(self.builtins)

    @staticmethod
    @lru_cache.lru_cache()
    def get_default():
        """
        When only one DjangoTemplates backend is configured, returns it.

        Raises ImproperlyConfigured otherwise.

        This is required for preserving historical APIs that rely on a
        globally available, implicitly configured engine such as:

        >>> from django.template import Context, Template
        >>> template = Template("Hello {{ name }}!")
        >>> context = Context({'name': "world"})
        >>> template.render(context)
        'Hello world!'
        """
        # Since Engine is imported in django.template and since
        # DjangoTemplates is a wrapper around this Engine class,
        # local imports are required to avoid import loops.
        from django.template import engines
        from django.template.backends.django import DjangoTemplates
        django_engines = [engine for engine in engines.all()
                          if isinstance(engine, DjangoTemplates)]
        if len(django_engines) == 1:
            # Unwrap the Engine instance inside DjangoTemplates
            return django_engines[0].engine
        elif len(django_engines) == 0:
            raise ImproperlyConfigured(
                "No DjangoTemplates backend is configured.")
        else:
            raise ImproperlyConfigured(
                "Several DjangoTemplates backends are configured. "
                "You must select one explicitly.")

    @cached_property
    def template_context_processors(self):
        context_processors = _builtin_context_processors
        context_processors += tuple(self.context_processors)
        return tuple(import_string(path) for path in context_processors)

    def get_template_builtins(self, builtins):
        return [import_library(x) for x in builtins]

    def get_template_libraries(self, libraries):
        loaded = {}
        for name, path in libraries.items():
            loaded[name] = import_library(path)
        return loaded

    @cached_property
    def template_loaders(self):
        return self.get_template_loaders(self.loaders)

    def get_template_loaders(self, template_loaders):
        loaders = []
        for template_loader in template_loaders:
            loader = self.find_template_loader(template_loader)
            if loader is not None:
                loaders.append(loader)
        return loaders

    def find_template_loader(self, loader):
        if isinstance(loader, (tuple, list)):
            args = list(loader[1:])
            loader = loader[0]
        else:
            args = []

        if isinstance(loader, six.string_types):
            loader_class = import_string(loader)
            return loader_class(self, *args)
        else:
            raise ImproperlyConfigured(
                "Invalid value in template loaders configuration: %r" % loader)

    def find_template(self, name, dirs=None, skip=None):
        tried = []
        for loader in self.template_loaders:
            if loader.supports_recursion:
                try:
                    template = loader.get_template(
                        name, template_dirs=dirs, skip=skip,
                    )
                    return template, template.origin
                except TemplateDoesNotExist as e:
                    tried.extend(e.tried)
            else:
                # RemovedInDjango20Warning: Use old api for non-recursive
                # loaders.
                try:
                    return loader(name, dirs)
                except TemplateDoesNotExist:
                    pass
        raise TemplateDoesNotExist(name, tried=tried)

    def from_string(self, template_code):
        """
        Returns a compiled Template object for the given template code,
        handling template inheritance recursively.
        """
        return Template(template_code, engine=self)

    def get_template(self, template_name):
        """
        Returns a compiled Template object for the given template name,
        handling template inheritance recursively.
        """
        template, origin = self.find_template(template_name)
        if not hasattr(template, 'render'):
            # template needs to be compiled
            template = Template(template, origin, template_name, engine=self)
        return template

    def render_to_string(self, template_name, context=None):
        """
        Render the template specified by template_name with the given context.
        For use in Django's test suite.
        """
        if isinstance(template_name, (list, tuple)):
            t = self.select_template(template_name)
        else:
            t = self.get_template(template_name)
        # Django < 1.8 accepted a Context in `context` even though that's
        # unintended. Preserve this ability but don't rewrap `context`.
        if isinstance(context, Context):
            return t.render(context)
        else:
            return t.render(Context(context))

    def select_template(self, template_name_list):
        """
        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 self.get_template(template_name)
            except TemplateDoesNotExist as exc:
                if exc.args[0] not in not_found:
                    not_found.append(exc.args[0])
                continue
        # If we get here, none of the templates could be loaded
        raise TemplateDoesNotExist(', '.join(not_found))