======================
The form rendering API
======================

.. module:: django.forms.renderers
   :synopsis: Built-in form renderers.

Django's form widgets are rendered using Django's :doc:`template engines
system </topics/templates>`.

The form rendering process can be customized at several levels:

* Widgets can specify custom template names.
* Forms and widgets can specify custom renderer classes.
* A widget's template can be overridden by a project. (Reusable applications
  typically shouldn't override built-in templates because they might conflict
  with a project's custom templates.)

.. _low-level-widget-render-api:

The low-level render API
========================

The rendering of form templates is controlled by a customizable renderer class.
A custom renderer can be specified by updating the :setting:`FORM_RENDERER`
setting. It defaults to
``'``:class:`django.forms.renderers.DjangoTemplates`\ ``'``.

By specifying a custom form renderer and overriding
:attr:`~.BaseRenderer.form_template_name` you can adjust the default form
markup across your project from a single place.

You can also provide a custom renderer per-form or per-widget by setting the
:attr:`.Form.default_renderer` attribute or by using the ``renderer`` argument
of :meth:`.Form.render`, or :meth:`.Widget.render`.

Matching points apply to formset rendering. See :ref:`formset-rendering` for
discussion.

Use one of the :ref:`built-in template form renderers
<built-in-template-form-renderers>` or implement your own. Custom renderers
must implement a ``render(template_name, context, request=None)`` method. It
should return a rendered template (as a string) or raise
:exc:`~django.template.TemplateDoesNotExist`.

.. class:: BaseRenderer

    The base class for the built-in form renderers.

    .. attribute:: form_template_name

        The default name of the template to use to render a form.

        Defaults to ``"django/forms/div.html"`` template.

    .. attribute:: formset_template_name

        The default name of the template to use to render a formset.

        Defaults to ``"django/forms/formsets/div.html"`` template.

    .. attribute:: field_template_name

        The default name of the template used to render a ``BoundField``.

        Defaults to ``"django/forms/field.html"``

    .. attribute:: bound_field_class

        The default class used to represent form fields across the project.

        Defaults to :class:`.BoundField` class.

        This can be customized further using :attr:`.Form.bound_field_class`
        for per-form overrides, or :attr:`.Field.bound_field_class` for
        per-field overrides.

    .. method:: get_template(template_name)

        Subclasses must implement this method with the appropriate template
        finding logic.

    .. method:: render(template_name, context, request=None)

        Renders the given template, or raises
        :exc:`~django.template.TemplateDoesNotExist`.

.. _built-in-template-form-renderers:

Built-in-template form renderers
================================

``DjangoTemplates``
-------------------

.. class:: DjangoTemplates

This renderer uses a standalone
:class:`~django.template.backends.django.DjangoTemplates`
engine (unconnected to what you might have configured in the
:setting:`TEMPLATES` setting). It loads templates first from the built-in form
templates directory in :source:`django/forms/templates` and then from the
installed apps' templates directories using the :class:`app_directories
<django.template.loaders.app_directories.Loader>` loader.

If you want to render templates with customizations from your
:setting:`TEMPLATES` setting, such as context processors for example, use the
:class:`TemplatesSetting` renderer.

``Jinja2``
----------

.. class:: Jinja2

This renderer is the same as the :class:`DjangoTemplates` renderer except that
it uses a :class:`~django.template.backends.jinja2.Jinja2` backend. Templates
for the built-in widgets are located in :source:`django/forms/jinja2` and
installed apps can provide templates in a ``jinja2`` directory.

To use this backend, all the forms and widgets in your project and its
third-party apps must have Jinja2 templates. Unless you provide your own Jinja2
templates for widgets that don't have any, you can't use this renderer. For
example, :mod:`django.contrib.admin` doesn't include Jinja2 templates for its
widgets due to their usage of Django template tags.

``TemplatesSetting``
--------------------

.. class:: TemplatesSetting

This renderer gives you complete control of how form and widget templates are
sourced. It uses :func:`~django.template.loader.get_template` to find templates
based on what's configured in the :setting:`TEMPLATES` setting.

Using this renderer along with the built-in templates requires either:

* ``'django.forms'`` in :setting:`INSTALLED_APPS` and at least one engine
  with :setting:`APP_DIRS=True <TEMPLATES-APP_DIRS>`.

* Adding the built-in templates directory in :setting:`DIRS <TEMPLATES-DIRS>`
  of one of your template engines. To generate that path::

    import django

    django.__path__[0] + "/forms/templates"  # or '/forms/jinja2'

Using this renderer requires you to make sure the form templates your project
needs can be located.

Context available in formset templates
======================================

Formset templates receive a context from :meth:`.BaseFormSet.get_context`. By
default, formsets receive a dictionary with the following values:

* ``formset``: The formset instance.

Context available in form templates
===================================

Form templates receive a context from :meth:`.Form.get_context`. By default,
forms receive a dictionary with the following values:

* ``form``: The bound form.
* ``fields``: All bound fields, except the hidden fields.
* ``hidden_fields``: All hidden bound fields.
* ``errors``: All non field related or hidden field related form errors.

Context available in field templates
====================================

Field templates receive a context from :meth:`.BoundField.get_context`. By
default, fields receive a dictionary with the following values:

* ``field``: The :class:`~django.forms.BoundField`.

Context available in widget templates
=====================================

Widget templates receive a context from :meth:`.Widget.get_context`. By
default, widgets receive a single value in the context, ``widget``. This is a
dictionary that contains values like:

* ``name``
* ``value``
* ``attrs``
* ``is_hidden``
* ``template_name``

Some widgets add further information to the context. For instance, all widgets
that subclass ``Input`` defines ``widget['type']`` and :class:`.MultiWidget`
defines ``widget['subwidgets']`` for looping purposes.

.. _overriding-built-in-formset-templates:

Overriding built-in formset templates
=====================================

:attr:`.BaseFormSet.template_name`

To override formset templates, you must use the :class:`TemplatesSetting`
renderer. Then overriding formset templates works :doc:`the same as
</howto/overriding-templates>` overriding any other template in your project.

.. _overriding-built-in-form-templates:

Overriding built-in form templates
==================================

:attr:`.Form.template_name`

To override form templates, you must use the :class:`TemplatesSetting`
renderer. Then overriding form templates works :doc:`the same as
</howto/overriding-templates>` overriding any other template in your project.

.. _overriding-built-in-field-templates:

Overriding built-in field templates
===================================

:attr:`.Field.template_name`

To override field templates, you must use the :class:`TemplatesSetting`
renderer. Then overriding field templates works :doc:`the same as
</howto/overriding-templates>` overriding any other template in your project.

.. _overriding-built-in-widget-templates:

Overriding built-in widget templates
====================================

Each widget has a ``template_name`` attribute with a value such as
``input.html``. Built-in widget templates are stored in the
``django/forms/widgets`` path. You can provide a custom template for
``input.html`` by defining ``django/forms/widgets/input.html``, for example.
See :ref:`built-in widgets` for the name of each widget's template.

To override widget templates, you must use the :class:`TemplatesSetting`
renderer. Then overriding widget templates works :doc:`the same as
</howto/overriding-templates>` overriding any other template in your project.
