Working with forms
About this document
This document provides an introduction to the basics of web forms and how they are handled in Django. For a more detailed look at specific areas of the forms API, see The Forms API, Form fields, and Form and field validation.
Unless you’re planning to build websites and applications that do nothing but publish content, and don’t accept input from your visitors, you’re going to need to understand and use forms.
Django provides a range of tools and libraries to help you build forms to accept input from site visitors, and then process and respond to the input.
HTML forms
In HTML, a form is a collection of elements inside <form>...</form>
that
allow a visitor to do things like enter text, select options, manipulate
objects or controls, and so on, and then send that information back to the
server.
Some of these form interface elements - text input or checkboxes - are fairly
simple and are built into HTML itself. Others are much more complex; an
interface that pops up a date picker or allows you to move a slider or
manipulate controls will typically use JavaScript and CSS as well as HTML form
<input>
elements to achieve these effects.
As well as its <input>
elements, a form must specify two things:
- where: the URL to which the data corresponding to the user’s input should be returned
- how: the HTTP method the data should be returned by
As an example, the login form for the Django admin contains several
<input>
elements: one of type="text"
for the username, one of
type="password"
for the password, and one of type="submit"
for the
“Log in” button. It also contains some hidden text fields that the user
doesn’t see, which Django uses to determine what to do next.
It also tells the browser that the form data should be sent to the URL
specified in the <form>
’s action
attribute - /admin/
- and that it
should be sent using the HTTP mechanism specified by the method
attribute -
post
.
When the <input type="submit" value="Log in">
element is triggered, the
data is returned to /admin/
.
GET
and POST
GET
and POST
are the only HTTP methods to use when dealing with forms.
Django’s login form is returned using the POST
method, in which the browser
bundles up the form data, encodes it for transmission, sends it to the server,
and then receives back its response.
GET
, by contrast, bundles the submitted data into a string, and uses this
to compose a URL. The URL contains the address where the data must be sent, as
well as the data keys and values. You can see this in action if you do a search
in the Django documentation, which will produce a URL of the form
https://docs.djangoproject.com/search/?q=forms&release=1
.
GET
and POST
are typically used for different purposes.
Any request that could be used to change the state of the system - for example,
a request that makes changes in the database - should use POST
. GET
should be used only for requests that do not affect the state of the system.
GET
would also be unsuitable for a password form, because the password
would appear in the URL, and thus, also in browser history and server logs,
all in plain text. Neither would it be suitable for large quantities of data,
or for binary data, such as an image. A Web application that uses GET
requests for admin forms is a security risk: it can be easy for an attacker to
mimic a form’s request to gain access to sensitive parts of the system.
POST
, coupled with other protections like Django’s CSRF protection offers more control over access.
On the other hand, GET
is suitable for things like a web search form,
because the URLs that represent a GET
request can easily be bookmarked,
shared, or resubmitted.
Django’s role in forms
Handling forms is a complex business. Consider Django’s admin, where numerous items of data of several different types may need to be prepared for display in a form, rendered as HTML, edited using a convenient interface, returned to the server, validated and cleaned up, and then saved or passed on for further processing.
Django’s form functionality can simplify and automate vast portions of this work, and can also do it more securely than most programmers would be able to do in code they wrote themselves.
Django handles three distinct parts of the work involved in forms:
- preparing and restructuring data to make it ready for rendering
- creating HTML forms for the data
- receiving and processing submitted forms and data from the client
It is possible to write code that does all of this manually, but Django can take care of it all for you.
Forms in Django
We’ve described HTML forms briefly, but an HTML <form>
is just one part of
the machinery required.
In the context of a Web application, ‘form’ might refer to that HTML
<form>
, or to the Django Form
that produces it, or to the
structured data returned when it is submitted, or to the end-to-end working
collection of these parts.
The Django Form
class
At the heart of this system of components is Django’s Form
class. In
much the same way that a Django model describes the logical structure of an
object, its behavior, and the way its parts are represented to us, a
Form
class describes a form and determines how it works and appears.
In a similar way that a model class’s fields map to database fields, a form
class’s fields map to HTML form <input>
elements. (A ModelForm
maps a model class’s fields to HTML form <input>
elements via a
Form
; this is what the Django admin is based upon.)
A form’s fields are themselves classes; they manage form data and perform
validation when a form is submitted. A DateField
and a
FileField
handle very different kinds of data and have to do
different things with it.
A form field is represented to a user in the browser as an HTML “widget” - a piece of user interface machinery. Each field type has an appropriate default Widget class, but these can be overridden as required.
Instantiating, processing, and rendering forms
When rendering an object in Django, we generally:
- get hold of it in the view (fetch it from the database, for example)
- pass it to the template context
- expand it to HTML markup using template variables
Rendering a form in a template involves nearly the same work as rendering any other kind of object, but there are some key differences.
In the case of a model instance that contained no data, it would rarely if ever be useful to do anything with it in a template. On the other hand, it makes perfect sense to render an unpopulated form - that’s what we do when we want the user to populate it.
So when we handle a model instance in a view, we typically retrieve it from the database. When we’re dealing with a form we typically instantiate it in the view.
When we instantiate a form, we can opt to leave it empty or pre-populate it, for example with:
- data from a saved model instance (as in the case of admin forms for editing)
- data that we have collated from other sources
- data received from a previous HTML form submission
The last of these cases is the most interesting, because it’s what makes it possible for users not just to read a website, but to send information back to it too.
Building a form
The work that needs to be done
Suppose you want to create a simple form on your website, in order to obtain the user’s name. You’d need something like this in your template:
<form action="/your-name/" method="post">
<label for="your_name">Your name: </label>
<input id="your_name" type="text" name="your_name" value="{{ current_name }}">
<input type="submit" value="OK">
</form>
This tells the browser to return the form data to the URL /your-name/
, using
the POST
method. It will display a text field, labeled “Your name:”, and a
button marked “OK”. If the template context contains a current_name
variable, that will be used to pre-fill the your_name
field.
You’ll need a view that renders the template containing the HTML form, and
that can supply the current_name
field as appropriate.
When the form is submitted, the POST
request which is sent to the server
will contain the form data.
Now you’ll also need a view corresponding to that /your-name/
URL which will
find the appropriate key/value pairs in the request, and then process them.
This is a very simple form. In practice, a form might contain dozens or hundreds of fields, many of which might need to be pre-populated, and we might expect the user to work through the edit-submit cycle several times before concluding the operation.
We might require some validation to occur in the browser, even before the form is submitted; we might want to use much more complex fields, that allow the user to do things like pick dates from a calendar and so on.
At this point it’s much easier to get Django to do most of this work for us.
Building a form in Django
The Form
class
We already know what we want our HTML form to look like. Our starting point for it in Django is this:
from django import forms
class NameForm(forms.Form):
your_name = forms.CharField(label='Your name', max_length=100)
This defines a Form
class with a single field (your_name
). We’ve
applied a human-friendly label to the field, which will appear in the
<label>
when it’s rendered (although in this case, the label
we specified is actually the same one that would be generated automatically if
we had omitted it).
The field’s maximum allowable length is defined by
max_length
. This does two things. It puts a
maxlength="100"
on the HTML <input>
(so the browser should prevent the
user from entering more than that number of characters in the first place). It
also means that when Django receives the form back from the browser, it will
validate the length of the data.
A Form
instance has an is_valid()
method, which runs
validation routines for all its fields. When this method is called, if all
fields contain valid data, it will:
- return
True
- place the form’s data in its
cleaned_data
attribute.
The whole form, when rendered for the first time, will look like:
<label for="your_name">Your name: </label>
<input id="your_name" type="text" name="your_name" maxlength="100" required>
Note that it does not include the <form>
tags, or a submit button.
We’ll have to provide those ourselves in the template.
The view
Form data sent back to a Django website is processed by a view, generally the same view which published the form. This allows us to reuse some of the same logic.
To handle the form we need to instantiate it in the view for the URL where we want it to be published:
from django.shortcuts import render
from django.http import HttpResponseRedirect
from .forms import NameForm
def get_name(request):
# if this is a POST request we need to process the form data
if request.method == 'POST':
# create a form instance and populate it with data from the request:
form = NameForm(request.POST)
# check whether it's valid:
if form.is_valid():
# process the data in form.cleaned_data as required
# ...
# redirect to a new URL:
return HttpResponseRedirect('/thanks/')
# if a GET (or any other method) we'll create a blank form
else:
form = NameForm()
return render(request, 'name.html', {'form': form})
If we arrive at this view with a GET
request, it will create an empty form
instance and place it in the template context to be rendered. This is what we
can expect to happen the first time we visit the URL.
If the form is submitted using a POST
request, the view will once again
create a form instance and populate it with data from the request: form =
NameForm(request.POST)
This is called “binding data to the form” (it is now
a bound form).
We call the form’s is_valid()
method; if it’s not True
, we go back to
the template with the form. This time the form is no longer empty (unbound)
so the HTML form will be populated with the data previously submitted, where it
can be edited and corrected as required.
If is_valid()
is True
, we’ll now be able to find all the validated form
data in its cleaned_data
attribute. We can use this data to update the
database or do other processing before sending an HTTP redirect to the browser
telling it where to go next.
The template
We don’t need to do much in our name.html
template. The simplest example
is:
<form action="/your-name/" method="post">
{% csrf_token %}
{{ form }}
<input type="submit" value="Submit">
</form>
All the form’s fields and their attributes will be unpacked into HTML markup
from that {{ form }}
by Django’s template language.
Forms and Cross Site Request Forgery protection
Django ships with an easy-to-use protection against Cross Site Request
Forgeries. When submitting a form via POST
with
CSRF protection enabled you must use the csrf_token
template tag
as in the preceding example. However, since CSRF protection is not
directly tied to forms in templates, this tag is omitted from the
following examples in this document.
HTML5 input types and browser validation
If your form includes a URLField
, an
EmailField
or any integer field type, Django will
use the url
, email
and number
HTML5 input types. By default,
browsers may apply their own validation on these fields, which may be
stricter than Django’s validation. If you would like to disable this
behavior, set the novalidate attribute on the form
tag, or specify
a different widget on the field, like TextInput
.
We now have a working web form, described by a Django Form
, processed
by a view, and rendered as an HTML <form>
.
That’s all you need to get started, but the forms framework puts a lot more at your fingertips. Once you understand the basics of the process described above, you should be prepared to understand other features of the forms system and ready to learn a bit more about the underlying machinery.
More about Django Form
classes
All form classes are created as subclasses of either django.forms.Form
or django.forms.ModelForm
. You can think of ModelForm
as a
subclass of Form
. Form
and ModelForm
actually inherit common
functionality from a (private) BaseForm
class, but this implementation
detail is rarely important.
Models and Forms
In fact if your form is going to be used to directly add or edit a Django
model, a ModelForm can save you a great
deal of time, effort, and code, because it will build a form, along with the
appropriate fields and their attributes, from a Model
class.
Bound and unbound form instances
The distinction between Bound and unbound forms is important:
- An unbound form has no data associated with it. When rendered to the user, it will be empty or will contain default values.
- A bound form has 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 what data to correct.
The form’s is_bound
attribute will tell you whether a form has
data bound to it or not.
More on fields
Consider a more useful form than our minimal example above, which we could use to implement “contact me” functionality on a personal website:
from django import forms
class ContactForm(forms.Form):
subject = forms.CharField(max_length=100)
message = forms.CharField(widget=forms.Textarea)
sender = forms.EmailField()
cc_myself = forms.BooleanField(required=False)
Our earlier form used a single field, your_name
, a CharField
. 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 Form fields.
Widgets
Each form field has a corresponding Widget class,
which in turn corresponds to an HTML form widget such as <input
type="text">
.
In most cases, the field will have a sensible default widget. For example, by
default, a CharField
will have a TextInput
widget, that
produces an <input type="text">
in the HTML. If you needed <textarea>
instead, you’d specify the appropriate widget when defining your form field,
as we have done for the message
field.
Field data
Whatever the data submitted with a form, once it has been successfully
validated by calling is_valid()
(and is_valid()
has returned True
),
the validated form data will be in the form.cleaned_data
dictionary. This
data will have been nicely converted into Python types for you.
Note
You can still access the unvalidated data directly from request.POST
at
this point, but the validated data is better.
In the contact form example above, cc_myself
will be a boolean value.
Likewise, fields such as IntegerField
and FloatField
convert
values to a Python int
and float
respectively.
Here’s how the form data could be processed in the view that handles this form:
from django.core.mail import send_mail
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)
send_mail(subject, message, sender, recipients)
return HttpResponseRedirect('/thanks/')
Tip
For more on sending email from Django, see Sending email.
Some field types need some extra handling. For example, files that are uploaded
using a form need to be handled differently (they can be retrieved from
request.FILES
, rather than request.POST
). For details of how to handle
file uploads with your form, see Binding uploaded files to a form.
Working with form templates
All you need to do to get your form into a template is to place the form
instance into the template context. So if your form is called form
in the
context, {{ form }}
will render its <label>
and <input>
elements
appropriately.
Form rendering options
Additional form template furniture
Don’t forget that a form’s output does not include the surrounding
<form>
tags, or the form’s submit
control. You will have to provide
these yourself.
There are other output options though for the <label>
/<input>
pairs:
{{ form.as_table }}
will render them as table cells wrapped in<tr>
tags{{ form.as_p }}
will render them wrapped in<p>
tags{{ form.as_ul }}
will render them wrapped in<li>
tags
Note that you’ll have to provide the surrounding <table>
or <ul>
elements yourself.
Here’s the output of {{ form.as_p }}
for our ContactForm
instance:
<p><label for="id_subject">Subject:</label>
<input id="id_subject" type="text" name="subject" maxlength="100" required></p>
<p><label for="id_message">Message:</label>
<textarea name="message" id="id_message" required></textarea></p>
<p><label for="id_sender">Sender:</label>
<input type="email" name="sender" id="id_sender" required></p>
<p><label for="id_cc_myself">Cc myself:</label>
<input type="checkbox" name="cc_myself" id="id_cc_myself"></p>
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 in ensuring that
forms are accessible to assistive technology such as screen reader software.
You can also customize the way in which labels and ids are generated.
See Outputting forms as HTML for more on this.
Rendering fields manually
We don’t have to let Django unpack the form’s fields; we can do it manually if
we like (allowing us to reorder the fields, for example). Each field is
available as an attribute of the form using {{ form.name_of_field }}
, and
in a Django template, will be rendered appropriately. For example:
{{ form.non_field_errors }}
<div class="fieldWrapper">
{{ form.subject.errors }}
<label for="{{ form.subject.id_for_label }}">Email subject:</label>
{{ form.subject }}
</div>
<div class="fieldWrapper">
{{ form.message.errors }}
<label for="{{ form.message.id_for_label }}">Your message:</label>
{{ form.message }}
</div>
<div class="fieldWrapper">
{{ form.sender.errors }}
<label for="{{ form.sender.id_for_label }}">Your email address:</label>
{{ form.sender }}
</div>
<div class="fieldWrapper">
{{ form.cc_myself.errors }}
<label for="{{ form.cc_myself.id_for_label }}">CC yourself?</label>
{{ form.cc_myself }}
</div>
Complete <label>
elements can also be generated using the
label_tag()
. For example:
<div class="fieldWrapper">
{{ form.subject.errors }}
{{ form.subject.label_tag }}
{{ form.subject }}
</div>
Rendering form error messages
Of course, the price of this flexibility is more work. Until now we haven’t had
to worry about how to display form errors, because that’s taken care of for us.
In this example we have had to make sure we take care of any errors for each
field and any errors for the form as a whole. Note {{ form.non_field_errors
}}
at the top of the form and the template lookup for errors on each field.
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 %}
Non-field errors (and/or hidden field errors that are rendered at the top of
the form when using helpers like form.as_p()
) will be rendered with an
additional class of nonfield
to help distinguish them from field-specific
errors. For example, {{ form.non_field_errors }}
would look like:
<ul class="errorlist nonfield">
<li>Generic validation error</li>
</ul>
See The Forms API for more on errors, styling, and working with form attributes in templates.
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:
{% for field in form %}
<div class="fieldWrapper">
{{ field.errors }}
{{ field.label_tag }} {{ field }}
{% if field.help_text %}
<p class="help">{{ field.help_text|safe }}</p>
{% endif %}
</div>
{% endfor %}
Useful attributes on {{ field }}
include:
{{ field.label }}
- The label of the field, e.g.
Email address
. {{ field.label_tag }}
The field’s label wrapped in the appropriate HTML
<label>
tag. This includes the form’slabel_suffix
. For example, the defaultlabel_suffix
is a colon:<label for="id_email">Email address:</label>
{{ field.id_for_label }}
- The ID that will be used for this field (
id_email
in the example above). If you are constructing the label manually, you may want to use this in lieu oflabel_tag
. It’s also useful, for example, if you have some inline JavaScript and want to avoid hardcoding the field’s ID. {{ field.value }}
- The value of the field. e.g
someone@example.com
. {{ 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 andFalse
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 %}
{{ field.field }}
- The
Field
instance from the form class that thisBoundField
wraps. You can use it to accessField
attributes, e.g.{{ char_field.field.max_length }}
.
See also
For a complete list of attributes and methods, see
BoundField
.
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 include
tag to reuse it in other templates:
# In your form template:
{% include "form_snippet.html" %}
# 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 with
argument of the include
tag:
{% include "form_snippet.html" with form=comment_form %}
If you find yourself doing this often, you might consider creating a custom inclusion tag.
Further topics
This covers the basics, but forms can do a whole lot more:
- Formsets
- Using initial data with a formset
- Limiting the maximum number of forms
- Formset validation
- Validating the number of forms in a formset
- Dealing with ordering and deletion of forms
- Adding additional fields to a formset
- Passing custom parameters to formset forms
- Customizing a formset’s prefix
- Using a formset in views and templates
- Creating forms from models
- Form Assets (the
Media
class)
See also
- The Forms Reference
- Covers the full API reference, including form fields, form widgets, and form and field validation.