==================

Working with forms

==================

.. admonition:: About this document

    This document provides an introduction to Django's form handling features.

    For a more detailed look at specific areas of the forms API, see

    :doc:`/ref/forms/api`, :doc:`/ref/forms/fields`, and

    :doc:`/ref/forms/validation`.

.. highlightlang:: html+django

``django.forms`` is Django's form-handling library.

While it is possible to process form submissions just using Django's

:class:`~django.http.HttpRequest` class, using the form library takes care of a

number of common form-related tasks. Using it, you can:

    1. Display an HTML form with automatically generated form widgets.

    2. Check submitted data against a set of validation rules.

    3. Redisplay a form in the case of validation errors.

    4. Convert submitted form data to the relevant Python data types.

Overview

========

The library deals with these concepts:

.. glossary::

    Widget

        A class that corresponds to an HTML form widget, e.g.

        ``<input type="text">`` or ``<textarea>``. This handles rendering of the

        widget as HTML.

    Field

        A class that is responsible for doing validation, e.g.

        an ``EmailField`` that makes sure its data is a valid e-mail address.

    Form

        A collection of fields that knows how to validate itself and

        display itself as HTML.

    Form Media

        The CSS and JavaScript resources that are required to render a form.

The library is decoupled from the other Django components, such as the database

layer, views and templates. It relies only on Django settings, a couple of

``django.utils`` helper functions and Django's internationalization hooks (but

you're not required to be using internationalization features to use this

library).

Form objects

============

A Form object encapsulates a sequence of form fields and a collection of

validation rules that must be fulfilled in order for the form to be accepted.

Form classes are created as subclasses of ``django.forms.Form`` and

make use of a declarative style that you'll be familiar with if you've used

Django's database models.

For example, consider a form used to implement "contact me" functionality on a

personal Web site:

.. code-block:: python

    from django import forms

    class ContactForm(forms.Form):

        subject = forms.CharField(max_length=100)

        message = forms.CharField()

        sender = forms.EmailField()

        cc_myself = forms.BooleanField(required=False)

A form is composed of ``Field`` objects. In this case, our form has four

fields: ``subject``, ``message``, ``sender`` and ``cc_myself``. ``CharField``,

``EmailField`` and ``BooleanField`` are just three of the available field types;

a full list can be found in :doc:`/ref/forms/fields`.

If your form is going to be used to directly add or edit a Django model, you can

use a :doc:`ModelForm </topics/forms/modelforms>` to avoid duplicating your model

description.

Using a form in a view

----------------------

The standard pattern for processing a form in a view looks like this:

.. code-block:: python

   def contact(request):

       if request.method == 'POST': # If the form has been submitted...

           form = ContactForm(request.POST) # A form bound to the POST data

           if form.is_valid(): # All validation rules pass

               # Process the data in form.cleaned_data

               # ...

               return HttpResponseRedirect('/thanks/') # Redirect after POST

       else:

           form = ContactForm() # An unbound form

       return render_to_response('contact.html', {

           'form': form,

       })

There are three code paths here:

    1. If the form has not been submitted, an unbound instance of ContactForm is

       created and passed to the template.

    2. If the form has been submitted, a bound instance of the form is created

       using ``request.POST``. If the submitted data is valid, it is processed

       and the user is re-directed to a "thanks" page.

    3. If the form has been submitted but is invalid, the bound form instance is

       passed on to the template.

.. versionchanged:: 1.0

    The ``cleaned_data`` attribute was called ``clean_data`` in earlier releases.

The distinction between **bound** and **unbound** forms is important. An unbound

form does not have any data associated with it; when rendered to the user, it

will be empty or will contain default values. A bound form does have submitted

data, and hence can be used to tell if that data is valid. If an invalid bound

form is rendered it can include inline error messages telling the user where

they went wrong.

See :ref:`ref-forms-api-bound-unbound` for further information on the

differences between bound and unbound forms.

Handling file uploads with a form

---------------------------------

To see how to handle file uploads with your form see

:ref:`binding-uploaded-files` for more information.

Processing the data from a form

-------------------------------

Once ``is_valid()`` returns ``True``, you can process the form submission safe

in the knowledge that it conforms to the validation rules defined by your form.

While you could access ``request.POST`` directly at this point, it is better to

access ``form.cleaned_data``. This data has not only been validated but will

also be converted in to the relevant Python types for you. In the above example,

``cc_myself`` will be a boolean value. Likewise, fields such as ``IntegerField``

and ``FloatField`` convert values to a Python int and float respectively.

Extending the above example, here's how the form data could be processed:

.. code-block:: python

    if form.is_valid():

        subject = form.cleaned_data['subject']

        message = form.cleaned_data['message']

        sender = form.cleaned_data['sender']

        cc_myself = form.cleaned_data['cc_myself']

        recipients = ['info@example.com']

        if cc_myself:

            recipients.append(sender)

        from django.core.mail import send_mail

        send_mail(subject, message, sender, recipients)

        return HttpResponseRedirect('/thanks/') # Redirect after POST

For more on sending e-mail from Django, see :doc:`/topics/email`.

Displaying a form using a template

----------------------------------

Forms are designed to work with the Django template language. In the above

example, we passed our ``ContactForm`` instance to the template using the

context variable ``form``. Here's a simple example template::

    <form action="/contact/" method="post">

    {{ form.as_p }}

    <input type="submit" value="Submit" />

    </form>

The form only outputs its own fields; it is up to you to provide the surrounding

``<form>`` tags and the submit button.

``form.as_p`` will output the form with each form field and accompanying label

wrapped in a paragraph. Here's the output for our example template::

   <form action="/contact/" method="post">

   <p><label for="id_subject">Subject:</label>

       <input id="id_subject" type="text" name="subject" maxlength="100" /></p>

   <p><label for="id_message">Message:</label>

       <input type="text" name="message" id="id_message" /></p>

   <p><label for="id_sender">Sender:</label>

       <input type="text" name="sender" id="id_sender" /></p>

   <p><label for="id_cc_myself">Cc myself:</label>

       <input type="checkbox" name="cc_myself" id="id_cc_myself" /></p>

   <input type="submit" value="Submit" />

   </form>

Note that each form field has an ID attribute set to ``id_<field-name>``, which

is referenced by the accompanying label tag. This is important for ensuring

forms are accessible to assistive technology such as screen reader software. You

can also :ref:`customize the way in which labels and ids are generated

<ref-forms-api-configuring-label>`.

You can also use ``form.as_table`` to output table rows (you'll need to provide

your own ``<table>`` tags) and ``form.as_ul`` to output list items.

Customizing the form template

-----------------------------

If the default generated HTML is not to your taste, you can completely customize

the way a form is presented using the Django template language. Extending the

above example::

    <form action="/contact/" method="post">

        {{ form.non_field_errors }}

        <div class="fieldWrapper">

            {{ form.subject.errors }}

            <label for="id_subject">E-mail subject:</label>

            {{ form.subject }}

        </div>

        <div class="fieldWrapper">

            {{ form.message.errors }}

            <label for="id_message">Your message:</label>

            {{ form.message }}

        </div>

        <div class="fieldWrapper">

            {{ form.sender.errors }}

            <label for="id_sender">Your email address:</label>

            {{ form.sender }}

        </div>

        <div class="fieldWrapper">

            {{ form.cc_myself.errors }}

            <label for="id_cc_myself">CC yourself?</label>

            {{ form.cc_myself }}

        </div>

        <p><input type="submit" value="Send message" /></p>

    </form>

Each named form-field can be output to the template using

``{{ form.name_of_field }}``, which will produce the HTML needed to display the

form widget. Using ``{{ form.name_of_field.errors }}`` displays a list of form

errors, rendered as an unordered list. This might look like::

   <ul class="errorlist">

       <li>Sender is required.</li>

   </ul>

The list has a CSS class of ``errorlist`` to allow you to style its appearance.

If you wish to further customize the display of errors you can do so by looping

over them::

    {% if form.subject.errors %}

        <ol>

        {% for error in form.subject.errors %}

            <li><strong>{{ error|escape }}</strong></li>

        {% endfor %}

        </ol>

    {% endif %}

Looping over the form's fields

------------------------------

If you're using the same HTML for each of your form fields, you can reduce

duplicate code by looping through each field in turn using a ``{% for %}``

loop::

    <form action="/contact/" method="post">

        {% for field in form %}

            <div class="fieldWrapper">

                {{ field.errors }}

                {{ field.label_tag }}: {{ field }}

            </div>

        {% endfor %}

        <p><input type="submit" value="Send message" /></p>

    </form>

Within this loop, ``{{ field }}`` is an instance of :class:`BoundField`.

``BoundField`` also has the following attributes, which can be useful in your

templates:

    ``{{ field.label }}``

        The label of the field, e.g. ``E-mail address``.

    ``{{ field.label_tag }}``

        The field's label wrapped in the appropriate HTML ``<label>`` tag,

        e.g. ``<label for="id_email">E-mail address</label>``

    ``{{ field.html_name }}``

        The name of the field that will be used in the input element's name

        field. This takes the form prefix into account, if it has been set.

    ``{{ field.help_text }}``

        Any help text that has been associated with the field.

    ``{{ field.errors }}``

        Outputs a ``<ul class="errorlist">`` containing any validation errors

        corresponding to this field. You can customize the presentation of

        the errors with a ``{% for error in field.errors %}`` loop. In this

        case, each object in the loop is a simple string containing the error

        message.

    ``field.is_hidden``

        This attribute is ``True`` if the form field is a hidden field and

        ``False`` otherwise. It's not particularly useful as a template

        variable, but could be useful in conditional tests such as::

            {% if field.is_hidden %}

               {# Do something special #}

            {% endif %}

Looping over hidden and visible fields

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

If you're manually laying out a form in a template, as opposed to relying on

Django's default form layout, you might want to treat ``<input type="hidden">``

fields differently than non-hidden fields. For example, because hidden fields

don't display anything, putting error messages "next to" the field could cause

confusion for your users -- so errors for those fields should be handled

differently.

Django provides two methods on a form that allow you to loop over the hidden

and visible fields independently: ``hidden_fields()`` and

``visible_fields()``. Here's a modification of an earlier example that uses

these two methods::

    <form action="/contact/" method="post">

        {% for field in form.visible_fields %}

            <div class="fieldWrapper">

                {# Include the hidden fields in the form #}

                {% if forloop.first %}

                    {% for hidden in form.hidden_fields %}

                    {{ hidden }}

                    {% endfor %}

                {% endif %}

                {{ field.errors }}

                {{ field.label_tag }}: {{ field }}

            </div>

        {% endfor %}

        <p><input type="submit" value="Send message" /></p>

    </form>

This example does not handle any errors in the hidden fields. Usually, an

error in a hidden field is a sign of form tampering, since normal form

interaction won't alter them. However, you could easily insert some error

displays for those form errors, as well.

.. versionadded:: 1.1

    The ``hidden_fields`` and ``visible_fields`` methods are new in Django

    1.1.

Reusable form templates

-----------------------

If your site uses the same rendering logic for forms in multiple places, you

can reduce duplication by saving the form's loop in a standalone template and

using the :ttag:`include` tag to reuse it in other templates::

    <form action="/contact/" method="post">

        {% include "form_snippet.html" %}

        <p><input type="submit" value="Send message" /></p>

    </form>

    # In form_snippet.html:

    {% for field in form %}

        <div class="fieldWrapper">

            {{ field.errors }}

            {{ field.label_tag }}: {{ field }}

        </div>

    {% endfor %}

If the form object passed to a template has a different name within the

context, you can alias it using the :ttag:`with` tag::

    <form action="/comments/add/" method="post">

        {% with comment_form as form %}

            {% include "form_snippet.html" %}

        {% endwith %}

        <p><input type="submit" value="Submit comment" /></p>

    </form>

If you find yourself doing this often, you might consider creating a custom

:ref:`inclusion tag<howto-custom-template-tags-inclusion-tags>`.

Further topics

==============

This covers the basics, but forms can do a whole lot more:

.. toctree::

   :maxdepth: 2

   modelforms

   formsets

   media

.. seealso::

    :doc:`The Forms Reference </ref/forms/index>`

        Covers the full API reference, including form fields, form widgets, 

        and form and field validation.