696 lines
24 KiB
Plaintext
696 lines
24 KiB
Plaintext
=========
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Templates
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=========
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.. module:: django.template
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:synopsis: Django's template system
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Being a web framework, Django needs a convenient way to generate HTML
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dynamically. The most common approach relies on templates. A template contains
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the static parts of the desired HTML output as well as some special syntax
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describing how dynamic content will be inserted. For a hands-on example of
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creating HTML pages with templates, see :doc:`Tutorial 3 </intro/tutorial03>`.
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A Django project can be configured with one or several template engines (or
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even zero if you don't use templates). Django ships built-in backends for its
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own template system, creatively called the Django template language (DTL), and
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for the popular alternative Jinja2_. Backends for other template languages may
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be available from third-parties.
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Django defines a standard API for loading and rendering templates regardless
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of the backend. Loading consists of finding the template for a given identifier
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and preprocessing it, usually compiling it to an in-memory representation.
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Rendering means interpolating the template with context data and returning the
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resulting string.
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The :doc:`Django template language </ref/templates/language>` is Django's own
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template system. Until Django 1.8 it was the only built-in option available.
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It's a good template library even though it's fairly opinionated and sports a
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few idiosyncrasies. If you don't have a pressing reason to choose another
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backend, you should use the DTL, especially if you're writing a pluggable
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application and you intend to distribute templates. Django's contrib apps that
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include templates, like :doc:`django.contrib.admin </ref/contrib/admin/index>`,
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use the DTL.
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For historical reasons, both the generic support for template engines and the
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implementation of the Django template language live in the ``django.template``
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namespace.
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.. _template-engines:
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Support for template engines
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============================
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.. versionadded:: 1.8
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Support for multiple template engines and the :setting:`TEMPLATES` setting
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were added in Django 1.8.
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Configuration
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-------------
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Templates engines are configured with the :setting:`TEMPLATES` setting. It's a
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list of configurations, one for each engine. The default value is empty. The
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``settings.py`` generated by the :djadmin:`startproject` command defines a
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more useful value::
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TEMPLATES = [
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{
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'BACKEND': 'django.template.backends.django.DjangoTemplates',
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'DIRS': [],
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'APP_DIRS': True,
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'OPTIONS': {
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# ... some options here ...
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},
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},
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]
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:setting:`BACKEND <TEMPLATES-BACKEND>` is a dotted Python path to a template
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engine class implementing Django's template backend API. The built-in backends
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are :class:`django.template.backends.django.DjangoTemplates` and
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:class:`django.template.backends.jinja2.Jinja2`.
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Since most engines load templates from files, the top-level configuration for
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each engine contains two common settings:
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* :setting:`DIRS <TEMPLATES-DIRS>` defines a list of directories where the
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engine should look for template source files, in search order.
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* :setting:`APP_DIRS <TEMPLATES-APP_DIRS>` tells whether the engine should
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look for templates inside installed applications. Each backend defines a
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conventional name for the subdirectory inside applications where its
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templates should be stored.
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While uncommon, it's possible to configure several instances of the same
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backend with different options. In that case you should define a unique
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:setting:`NAME <TEMPLATES-NAME>` for each engine.
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:setting:`OPTIONS <TEMPLATES-OPTIONS>` contains backend-specific settings.
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Usage
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-----
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.. _template-loading:
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.. module:: django.template.loader
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The ``django.template.loader`` module defines two functions to load templates.
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.. function:: get_template(template_name[, dirs][, using])
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This function loads the template with the given name and returns a
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``Template`` object.
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The exact type of the return value depends on the backend that loaded the
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template. Each backend has its own ``Template`` class.
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``get_template()`` tries each template engine in order until one succeeds.
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If the template cannot be found, it raises
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:exc:`~django.template.TemplateDoesNotExist`. If the template is found but
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contains invalid syntax, it raises
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:exc:`~django.template.TemplateSyntaxError`.
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How templates are searched and loaded depends on each engine's backend and
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configuration.
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If you want to restrict the search to a particular template engine, pass
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the engine's :setting:`NAME <TEMPLATES-NAME>` in the ``using`` argument.
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.. versionchanged:: 1.7
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The ``dirs`` parameter was added.
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.. deprecated:: 1.8
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The ``dirs`` parameter was deprecated.
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.. versionchanged:: 1.8
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The ``using`` parameter was added.
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.. versionchanged:: 1.8
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``get_template()`` returns a backend-dependent ``Template`` instead
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of a :class:`django.template.Template`.
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.. function:: select_template(template_name_list[, dirs][, using])
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``select_template()`` is just like ``get_template()``, except it takes a
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list of template names. It tries each name in order and returns the first
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template that exists.
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.. versionchanged:: 1.7
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The ``dirs`` parameter was added.
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.. deprecated:: 1.8
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The ``dirs`` parameter was deprecated.
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.. versionchanged:: 1.8
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The ``using`` parameter was added.
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.. versionchanged:: 1.8
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``select_template()`` returns a backend-dependent ``Template`` instead
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of a :class:`django.template.Template`.
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.. currentmodule:: django.template
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If loading a template fails, the following two exceptions, defined in
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``django.template``, may be raised:
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.. exception:: TemplateDoesNotExist
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This exception is raised when a template cannot be found.
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.. exception:: TemplateSyntaxError
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This exception is raised when a template was found but contains errors.
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``Template`` objects returned by ``get_template()`` and ``select_template()``
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must provide a ``render()`` method with the following signature:
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.. currentmodule:: django.template.backends.base
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.. method:: Template.render(context=None, request=None)
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Renders this template with a given context.
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If ``context`` is provided, it must be a :class:`dict`. If it isn't
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provided, the engine will render the template with an empty context.
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If ``request`` is provided, it must be an :class:`~django.http.HttpRequest`.
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Then the engine must make it, as well as the CSRF token, available in the
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template. How this is achieved is up to each backend.
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Here's an example of the search algorithm. For this example the
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:setting:`TEMPLATES` setting is::
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TEMPLATES = [
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{
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'BACKEND': 'django.template.backends.django.DjangoTemplates',
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'DIRS': [
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'/home/html/example.com',
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'/home/html/default',
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],
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},
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{
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'BACKEND': 'django.template.backends.jinja2.Jinja2',
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'DIRS': [
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'/home/html/jinja2',
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],
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},
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]
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If you call ``get_template('story_detail.html')``, here are the files Django
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will look for, in order:
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* ``/home/html/example.com/story_detail.html`` (``'django'`` engine)
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* ``/home/html/default/story_detail.html`` (``'django'`` engine)
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* ``/home/html/jinja2/story_detail.html`` (``'jinja2'`` engine)
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If you call ``select_template(['story_253_detail.html', 'story_detail.html'])``,
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here's what Django will look for:
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* ``/home/html/example.com/story_253_detail.html`` (``'django'`` engine)
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* ``/home/html/default/story_253_detail.html`` (``'django'`` engine)
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* ``/home/html/jinja2/story_253_detail.html`` (``'jinja2'`` engine)
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* ``/home/html/example.com/story_detail.html`` (``'django'`` engine)
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* ``/home/html/default/story_detail.html`` (``'django'`` engine)
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* ``/home/html/jinja2/story_detail.html`` (``'jinja2'`` engine)
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When Django finds a template that exists, it stops looking.
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.. admonition:: Tip
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You can use :func:`~django.template.loader.select_template()` for flexible
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template loading. For example, if you've written a news story and want
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some stories to have custom templates, use something like
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``select_template(['story_%s_detail.html' % story.id,
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'story_detail.html'])``. That'll allow you to use a custom template for an
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individual story, with a fallback template for stories that don't have
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custom templates.
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It's possible -- and preferable -- to organize templates in subdirectories
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inside each directory containing templates. The convention is to make a
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subdirectory for each Django app, with subdirectories within those
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subdirectories as needed.
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Do this for your own sanity. Storing all templates in the root level of a
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single directory gets messy.
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To load a template that's within a subdirectory, just use a slash, like so::
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get_template('news/story_detail.html')
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Using the same :setting:`TEMPLATES` option as above, this will attempt to load
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the following templates:
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* ``/home/html/example.com/news/story_detail.html`` (``'django'`` engine)
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* ``/home/html/default/news/story_detail.html`` (``'django'`` engine)
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* ``/home/html/jinja2/news/story_detail.html`` (``'jinja2'`` engine)
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.. currentmodule:: django.template.loader
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In addition, to cut down on the repetitive nature of loading and rendering
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templates, Django provides a shortcut function which automates the process.
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.. function:: render_to_string(template_name[, context][, context_instance][, request][, using])
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``render_to_string()`` loads a template like :func:`get_template` and
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calls its ``render()`` method immediately. It takes the following
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arguments.
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``template_name``
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The name of the template to load and render. If it's a list of template
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names, Django uses :func:`select_template` instead of
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:func:`get_template` to find the template.
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``context``
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A :class:`dict` to be used as the template's context for rendering.
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.. versionchanged:: 1.8
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The ``context`` argument used to be called ``dictionary``. That name
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is deprecated in Django 1.8 and will be removed in Django 2.0.
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``context`` is now optional. An empty context will be used if it
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isn't provided.
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``context_instance``
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An instance of :class:`~django.template.Context` or a subclass (e.g., an
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instance of :class:`~django.template.RequestContext`) to use as the
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template's context.
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.. deprecated:: 1.8
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The ``context_instance`` argument is deprecated. Use ``context`` and
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if needed ``request``.
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``request``
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An optional :class:`~django.http.HttpRequest` that will be available
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during the template's rendering process.
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.. versionadded:: 1.8
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The ``request`` argument was added.
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See also the :func:`~django.shortcuts.render()` and
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:func:`~django.shortcuts.render_to_response()` shortcuts, which call
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:func:`render_to_string()` and feed the result into an
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:class:`~django.http.HttpResponse` suitable for returning from a view.
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Finally, you can use configured engines directly:
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.. data:: engines
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Template engines are available in ``django.template.engines``::
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from django.template import engines
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django_engine = engines['django']
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template = django_engine.from_string("Hello {{ name }}!")
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The lookup key — ``'django'`` in this example — is the engine's
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:setting:`NAME <TEMPLATES-NAME>`.
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.. module:: django.template.backends
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Built-in backends
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-----------------
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.. module:: django.template.backends.django
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.. class:: DjangoTemplates
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Set :setting:`BACKEND <TEMPLATES-BACKEND>` to
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``'django.template.backends.django.DjangoTemplates'`` to configure a Django
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template engine.
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When :setting:`APP_DIRS <TEMPLATES-APP_DIRS>` is ``True``, ``DjangoTemplates``
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engines look for templates in the ``templates`` subdirectory of installed
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applications. This generic name was kept for backwards-compatibility.
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``DjangoTemplates`` engines accept the following :setting:`OPTIONS
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<TEMPLATES-OPTIONS>`:
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* ``'allowed_include_roots'``: a list of strings representing allowed prefixes
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for the ``{% ssi %}`` template tag. This is a security measure, so that
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template authors can't access files that they shouldn't be accessing.
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For example, if ``'allowed_include_roots'`` is ``['/home/html',
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'/var/www']``, then ``{% ssi /home/html/foo.txt %}`` would work, but ``{%
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ssi /etc/passwd %}`` wouldn't.
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It defaults to an empty list.
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.. deprecated:: 1.8
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``allowed_include_roots`` is deprecated because the {% ssi %} tag is
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deprecated.
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* ``'context_processors'``: a list of dotted Python paths to callables that
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are used to populate the context when a template is rendered with a request.
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These callables take a request object as their argument and return a
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:class:`dict` of items to be merged into the context.
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It defaults to an empty list.
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See :class:`~django.template.RequestContext` for more information.
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* ``'debug'``: a boolean that turns on/off template debug mode. If it is
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``True``, the fancy error page will display a detailed report for any
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exception raised during template rendering. This report contains the
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relevant snippet of the template with the appropriate line highlighted.
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It defaults to the value of the :setting:`DEBUG` setting.
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* ``'loaders'``: a list of dotted Python paths to template loader classes.
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Each ``Loader`` class knows how to import templates from a particular
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source. Optionally, a tuple can be used instead of a string. The first item
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in the tuple should be the ``Loader`` class name, and subsequent items are
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passed to the ``Loader`` during initialization.
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The default depends on the values of :setting:`DIRS <TEMPLATES-DIRS>` and
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:setting:`APP_DIRS <TEMPLATES-APP_DIRS>`.
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See :ref:`template-loaders` for details.
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* ``'string_if_invalid'``: the output, as a string, that the template system
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should use for invalid (e.g. misspelled) variables.
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It defaults to an empty string.
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See :ref:`invalid-template-variables` for details.
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* ``'file_charset'``: the charset used to read template files on disk.
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It defaults to the value of :setting:`FILE_CHARSET`.
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.. module:: django.template.backends.jinja2
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.. class:: Jinja2
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Requires Jinja2_ to be installed:
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.. code-block:: console
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$ pip install Jinja2
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Set :setting:`BACKEND <TEMPLATES-BACKEND>` to
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``'django.template.backends.jinja2.Jinja2'`` to configure a Jinja2_ engine.
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When :setting:`APP_DIRS <TEMPLATES-APP_DIRS>` is ``True``, ``Jinja2`` engines
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look for templates in the ``jinja2`` subdirectory of installed applications.
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The most important entry in :setting:`OPTIONS <TEMPLATES-OPTIONS>` is
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``'environment'``. It's a dotted Python path to a callable returning a Jinja2
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environment. It defaults to ``'jinja2.Environment'``. Django invokes that
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callable and passes other options as keyword arguments. Furthermore, Django
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adds defaults that differ from Jinja2's for a few options:
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* ``'autoescape'``: ``True``
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* ``'loader'``: a loader configured for :setting:`DIRS <TEMPLATES-DIRS>` and
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:setting:`APP_DIRS <TEMPLATES-APP_DIRS>`
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* ``'auto_reload'``: ``settings.DEBUG``
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* ``'undefined'``: ``DebugUndefined if settings.DEBUG else Undefined``
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The default configuration is purposefully kept to a minimum. The ``Jinja2``
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backend doesn't create a Django-flavored environment. It doesn't know about
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Django context processors, filters, and tags. In order to use Django-specific
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APIs, you must configure them into the environment.
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For example, you can create ``myproject/jinja2.py`` with this content::
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from django.contrib.staticfiles.storage import staticfiles_storage
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from django.core.urlresolvers import reverse
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from jinja2 import Environment
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def environment(**options):
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env = Environment(**options)
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env.globals.update({
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'static': staticfiles_storage.url,
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'url': reverse,
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})
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return env
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and set the ``'environment'`` option to ``'myproject.jinja2.environment'``.
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Then you could use the following constructs in Jinja2 templates:
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.. code-block:: html+jinja
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<img src="{{ static('path/to/company-logo.png') }}" alt="Company Logo">
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<a href="{{ url('admin:index') }}">Administration</a>
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The concepts of tags and filters exist both in the Django template language
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and in Jinja2 but they're used differently. Since Jinja2 supports passing
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arguments to callables in templates, many features that require a template tag
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or filter in Django templates can be achieved simply by calling a function in
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Jinja2 templates, as shown in the example above. Jinja2's global namespace
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removes the need for template context processors. The Django template language
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doesn't have an equivalent of Jinja2 tests.
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Custom backends
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---------------
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Here's how to implement a custom template backend in order to use another
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template system. A template backend is a class that inherits
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``django.template.backends.base.BaseEngine``. It must implement
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``get_template()`` and optionally ``from_string()``. Here's an example for a
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fictional ``foobar`` template library::
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from django.template import TemplateDoesNotExist, TemplateSyntaxError
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from django.template.backends.base import BaseEngine
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from django.template.backends.utils import csrf_input_lazy, csrf_token_lazy
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import foobar
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class FooBar(BaseEngine):
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# Name of the subdirectory containing the templates for this engine
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# inside an installed application.
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app_dirname = 'foobar'
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def __init__(self, params):
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params = params.copy()
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options = params.pop('OPTIONS').copy()
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super(FooBar, self).__init__(params)
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self.engine = foobar.Engine(**options)
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def from_string(self, template_code):
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try:
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return Template(self.engine.from_string(template_code))
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except foobar.TemplateCompilationFailed as exc:
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raise TemplateSyntaxError(exc.args)
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def get_template(self, template_name):
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try:
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return Template(self.engine.get_template(template_name))
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except foobar.TemplateNotFound as exc:
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raise TemplateDoesNotExist(exc.args)
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except foobar.TemplateCompilationFailed as exc:
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raise TemplateSyntaxError(exc.args)
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class Template(object):
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def __init__(self, template):
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self.template = template
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def render(self, context=None, request=None):
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if context is None:
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context = {}
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if request is not None:
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context['request'] = request
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context['csrf_input'] = csrf_input_lazy(request)
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context['csrf_token'] = csrf_token_lazy(request)
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return self.template.render(context)
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See `DEP 182`_ for more information.
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.. currentmodule:: django.template
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.. _template-language-intro:
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The Django template language
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============================
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.. highlightlang:: html+django
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Syntax
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------
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.. admonition:: About this section
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This is an overview of the Django template language's syntax. For details
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see the :doc:`language syntax reference </ref/templates/language>`.
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A Django template is simply a text document or a Python string marked-up using
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the Django template language. Some constructs are recognized and interpreted
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by the template engine. The main ones are variables and tags.
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A template is rendered with a context. Rendering replaces variables with their
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values, which are looked up in the context, and executes tags. Everything else
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is output as is.
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The syntax of the Django template language involves four constructs.
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Variables
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~~~~~~~~~
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A variable outputs a value from the context, which is a dict-like object
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mapping keys to values.
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Variables are surrounded by ``{{`` and ``}}`` like this::
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My first name is {{ first_name }}. My last name is {{ last_name }}.
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With a context of ``{'first_name': 'John', 'last_name': 'Doe'}``, this
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template renders to::
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My first name is John. My last name is Doe.
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Dictionary lookup, attribute lookup and list-index lookups are implemented
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with a dot notation::
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{{ my_dict.key }}
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{{ my_object.attribute }}
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{{ my_list.0 }}
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If a variable resolves to a callable, the template system will call it with no
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arguments and use its result instead of the callable.
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Tags
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~~~~
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Tags provide arbitrary logic in the rendering process.
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This definition is deliberately vague. For example, a tag can output content,
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serve as a control structure e.g. an "if" statement or a "for" loop, grab
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content from a database, or even enable access to other template tags.
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Tags are surrounded by ``{%`` and ``%}`` like this::
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{% csrf_token %}
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Most tags accept arguments::
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{% cycle 'odd' 'even' %}
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Some tags require beginning and ending tags::
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{% if user.is_authenticated %}Hello, {{ user.username }}.{% endif %}
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A :ref:`reference of built-in tags <ref-templates-builtins-tags>` is
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available as well as :ref:`instructions for writing custom tags
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<howto-writing-custom-template-tags>`.
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Filters
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~~~~~~~
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Filters transform the values of variables and tag arguments.
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They look like this::
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{{ django|title }}
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With a context of ``{'django': 'the web framework for perfectionists with
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deadlines'}``, this template renders to::
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The Web Framework For Perfectionists With Deadlines
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Some filters take an argument::
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{{ my_date|date:"Y-m-d" }}
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A :ref:`reference of built-in filters <ref-templates-builtins-filters>` is
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available as well as :ref:`instructions for writing custom filters
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<howto-writing-custom-template-filters>`.
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Comments
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~~~~~~~~
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Comments look like this::
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{# this won't be rendered #}
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A :ttag:`{% comment %} <comment>` tag provides multi-line comments.
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Components
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----------
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.. admonition:: About this section
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This is an overview of the Django template language's APIs. For details
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see the :doc:`API reference </ref/templates/api>`.
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Engine
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~~~~~~
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:class:`django.template.Engine` encapsulates an instance of the Django
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template system. The main reason for instantiating an
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:class:`~django.template.Engine` directly is to use the Django template
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language outside of a Django project.
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:class:`django.template.backends.django.DjangoTemplates` is a thin wrapper
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adapting :class:`django.template.Engine` to Django's template backend API.
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Template
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~~~~~~~~
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:class:`django.template.Template` represents a compiled template.
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Templates are obtained with :meth:`Engine.get_template()
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<django.template.Engine.get_template>` or :meth:`Engine.from_string()
|
|
<django.template.Engine.from_string>`
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Likewise ``django.template.backends.django.Template`` is a thin wrapper
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adapting :class:`django.template.Template` to the common template API.
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Context
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~~~~~~~
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:class:`django.template.Context` holds some metadata in addition to the
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context data. It is passed to :meth:`Template.render()
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|
<django.template.Template.render>` for rendering a template.
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|
:class:`django.template.RequestContext` is a subclass of
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|
:class:`~django.template.Context` that stores the current
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:class:`~django.http.HttpRequest` and runs template context processors.
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The common API doesn't have an equivalent concept. Context data is passed in a
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plain :class:`dict` and the current :class:`~django.http.HttpRequest` is passed
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separately if needed.
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Loaders
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|
~~~~~~~
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|
Template loaders are responsible for locating templates, loading them, and
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returning :class:`~django.template.Template` objects.
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|
Django provides several :ref:`built-in template loaders <template-loaders>`
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|
and supports :ref:`custom template loaders <custom-template-loaders>`.
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|
Context processors
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|
~~~~~~~~~~~~~~~~~~
|
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|
Context processors are functions that receive the current
|
|
:class:`~django.http.HttpRequest` as an argument and return a :class:`dict` of
|
|
data to be added to the rendering context.
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|
Their main use is to add common data shared by all templates to the context
|
|
without repeating code in every view.
|
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|
Django provides many :ref:`built-in context processors <context-processors>`.
|
|
Implementing a custom context processor is as simple as defining a function.
|
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|
.. _Jinja2: http://jinja.pocoo.org/
|
|
.. _DEP 182: https://github.com/django/deps/blob/master/accepted/0182-multiple-template-engines.rst
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