The Forms API¶
About this document
This document covers the gritty details of Django’s forms API. You should read the introduction to working with forms first.
Bound and unbound forms¶
A Form
instance is either bound to a set of data, or unbound.
- If it’s bound to a set of data, it’s capable of validating that data and rendering the form as HTML with the data displayed in the HTML.
- If it’s unbound, it cannot do validation (because there’s no data to validate!), but it can still render the blank form as HTML.
To create an unbound Form
instance, instantiate the class:
>>> f = ContactForm()
To bind data to a form, pass the data as a dictionary as the first parameter to
your Form
class constructor:
>>> data = {'subject': 'hello',
... 'message': 'Hi there',
... 'sender': 'foo@example.com',
... 'cc_myself': True}
>>> f = ContactForm(data)
In this dictionary, the keys are the field names, which correspond to the
attributes in your Form
class. The values are the data you’re trying to
validate. These will usually be strings, but there’s no requirement that they be
strings; the type of data you pass depends on the Field
, as we’ll see
in a moment.
-
Form.
is_bound
¶
If you need to distinguish between bound and unbound form instances at runtime,
check the value of the form’s is_bound
attribute:
>>> f = ContactForm()
>>> f.is_bound
False
>>> f = ContactForm({'subject': 'hello'})
>>> f.is_bound
True
Note that passing an empty dictionary creates a bound form with empty data:
>>> f = ContactForm({})
>>> f.is_bound
True
If you have a bound Form
instance and want to change the data somehow,
or if you want to bind an unbound Form
instance to some data, create
another Form
instance. There is no way to change data in a
Form
instance. Once a Form
instance has been created, you
should consider its data immutable, whether it has data or not.
Using forms to validate data¶
-
Form.
clean
()¶
Implement a clean()
method on your Form
when you must add custom
validation for fields that are interdependent. See
Cleaning and validating fields that depend on each other for example usage.
-
Form.
is_valid
()¶
The primary task of a Form
object is to validate data. With a bound
Form
instance, call the is_valid()
method to run validation
and return a boolean designating whether the data was valid:
>>> data = {'subject': 'hello',
... 'message': 'Hi there',
... 'sender': 'foo@example.com',
... 'cc_myself': True}
>>> f = ContactForm(data)
>>> f.is_valid()
True
Let’s try with some invalid data. In this case, subject
is blank (an error,
because all fields are required by default) and sender
is not a valid
email address:
>>> data = {'subject': '',
... 'message': 'Hi there',
... 'sender': 'invalid email address',
... 'cc_myself': True}
>>> f = ContactForm(data)
>>> f.is_valid()
False
-
Form.
errors
¶
Access the errors
attribute to get a dictionary of error
messages:
>>> f.errors
{'sender': ['Enter a valid email address.'], 'subject': ['This field is required.']}
In this dictionary, the keys are the field names, and the values are lists of strings representing the error messages. The error messages are stored in lists because a field can have multiple error messages.
You can access errors
without having to call
is_valid()
first. The form’s data will be validated the first time
either you call is_valid()
or access errors
.
The validation routines will only get called once, regardless of how many times
you access errors
or call is_valid()
. This means that
if validation has side effects, those side effects will only be triggered once.
-
Form.errors.
as_data
()¶
Returns a dict
that maps fields to their original ValidationError
instances.
>>> f.errors.as_data()
{'sender': [ValidationError(['Enter a valid email address.'])],
'subject': [ValidationError(['This field is required.'])]}
Use this method anytime you need to identify an error by its code
. This
enables things like rewriting the error’s message or writing custom logic in a
view when a given error is present. It can also be used to serialize the errors
in a custom format (e.g. XML); for instance, as_json()
relies on as_data()
.
The need for the as_data()
method is due to backwards compatibility.
Previously ValidationError
instances were lost as soon as their
rendered error messages were added to the Form.errors
dictionary.
Ideally Form.errors
would have stored ValidationError
instances
and methods with an as_
prefix could render them, but it had to be done
the other way around in order not to break code that expects rendered error
messages in Form.errors
.
-
Form.errors.
as_json
(escape_html=False)¶
Returns the errors serialized as JSON.
>>> f.errors.as_json()
{"sender": [{"message": "Enter a valid email address.", "code": "invalid"}],
"subject": [{"message": "This field is required.", "code": "required"}]}
By default, as_json()
does not escape its output. If you are using it for
something like AJAX requests to a form view where the client interprets the
response and inserts errors into the page, you’ll want to be sure to escape the
results on the client-side to avoid the possibility of a cross-site scripting
attack. You can do this in JavaScript with element.textContent = errorText
or with jQuery’s $(el).text(errorText)
(rather than its .html()
function).
If for some reason you don’t want to use client-side escaping, you can also
set escape_html=True
and error messages will be escaped so you can use them
directly in HTML.
-
Form.errors.
get_json_data
(escape_html=False)¶
Returns the errors as a dictionary suitable for serializing to JSON.
Form.errors.as_json()
returns serialized JSON, while this returns the
error data before it’s serialized.
The escape_html
parameter behaves as described in
Form.errors.as_json()
.
-
Form.
add_error
(field, error)¶
This method allows adding errors to specific fields from within the
Form.clean()
method, or from outside the form altogether; for instance
from a view.
The field
argument is the name of the field to which the errors
should be added. If its value is None
the error will be treated as
a non-field error as returned by Form.non_field_errors()
.
The error
argument can be a string, or preferably an instance of
ValidationError
. See Raising ValidationError for best practices
when defining form errors.
Note that Form.add_error()
automatically removes the relevant field from
cleaned_data
.
-
Form.
has_error
(field, code=None)¶
This method returns a boolean designating whether a field has an error with
a specific error code
. If code
is None
, it will return True
if the field contains any errors at all.
To check for non-field errors use
NON_FIELD_ERRORS
as the field
parameter.
-
Form.
non_field_errors
()¶
This method returns the list of errors from Form.errors
that aren’t associated with a particular field.
This includes ValidationError
s that are raised in Form.clean()
and errors added using Form.add_error(None,
"...")
.
Behavior of unbound forms¶
It’s meaningless to validate a form with no data, but, for the record, here’s what happens with unbound forms:
>>> f = ContactForm()
>>> f.is_valid()
False
>>> f.errors
{}
Initial form values¶
-
Form.
initial
¶
Use initial
to declare the initial value of form fields at
runtime. For example, you might want to fill in a username
field with the
username of the current session.
To accomplish this, use the initial
argument to a Form
.
This argument, if given, should be a dictionary mapping field names to initial
values. Only include the fields for which you’re specifying an initial value;
it’s not necessary to include every field in your form. For example:
>>> f = ContactForm(initial={'subject': 'Hi there!'})
These values are only displayed for unbound forms, and they’re not used as fallback values if a particular value isn’t provided.
If a Field
defines initial
and you
include initial
when instantiating the Form
, then the latter
initial
will have precedence. In this example, initial
is provided both
at the field level and at the form instance level, and the latter gets
precedence:
>>> from django import forms
>>> class CommentForm(forms.Form):
... name = forms.CharField(initial='class')
... url = forms.URLField()
... comment = forms.CharField()
>>> f = CommentForm(initial={'name': 'instance'}, auto_id=False)
>>> print(f)
<tr><th>Name:</th><td><input type="text" name="name" value="instance" required></td></tr>
<tr><th>Url:</th><td><input type="url" name="url" required></td></tr>
<tr><th>Comment:</th><td><input type="text" name="comment" required></td></tr>
-
Form.
get_initial_for_field
(field, field_name)¶
Returns the initial data for a form field. It retrieves the data from
Form.initial
if present, otherwise trying Field.initial
.
Callable values are evaluated.
It is recommended to use BoundField.initial
over
get_initial_for_field()
because BoundField.initial
has a
simpler interface. Also, unlike get_initial_for_field()
,
BoundField.initial
caches its values. This is useful especially when
dealing with callables whose return values can change (e.g. datetime.now
or
uuid.uuid4
):
>>> import uuid
>>> class UUIDCommentForm(CommentForm):
... identifier = forms.UUIDField(initial=uuid.uuid4)
>>> f = UUIDCommentForm()
>>> f.get_initial_for_field(f.fields['identifier'], 'identifier')
UUID('972ca9e4-7bfe-4f5b-af7d-07b3aa306334')
>>> f.get_initial_for_field(f.fields['identifier'], 'identifier')
UUID('1b411fab-844e-4dec-bd4f-e9b0495f04d0')
>>> # Using BoundField.initial, for comparison
>>> f['identifier'].initial
UUID('28a09c59-5f00-4ed9-9179-a3b074fa9c30')
>>> f['identifier'].initial
UUID('28a09c59-5f00-4ed9-9179-a3b074fa9c30')
Checking which form data has changed¶
-
Form.
has_changed
()¶
Use the has_changed()
method on your Form
when you need to check if the
form data has been changed from the initial data.
>>> data = {'subject': 'hello',
... 'message': 'Hi there',
... 'sender': 'foo@example.com',
... 'cc_myself': True}
>>> f = ContactForm(data, initial=data)
>>> f.has_changed()
False
When the form is submitted, we reconstruct it and provide the original data so that the comparison can be done:
>>> f = ContactForm(request.POST, initial=data)
>>> f.has_changed()
has_changed()
will be True
if the data from request.POST
differs
from what was provided in initial
or False
otherwise. The
result is computed by calling Field.has_changed()
for each field in the
form.
-
Form.
changed_data
¶
The changed_data
attribute returns a list of the names of the fields whose
values in the form’s bound data (usually request.POST
) differ from what was
provided in initial
. It returns an empty list if no data differs.
>>> f = ContactForm(request.POST, initial=data)
>>> if f.has_changed():
... print("The following fields changed: %s" % ", ".join(f.changed_data))
>>> f.changed_data
['subject', 'message']
Accessing the fields from the form¶
-
Form.
fields
¶
You can access the fields of Form
instance from its fields
attribute:
>>> for row in f.fields.values(): print(row)
...
<django.forms.fields.CharField object at 0x7ffaac632510>
<django.forms.fields.URLField object at 0x7ffaac632f90>
<django.forms.fields.CharField object at 0x7ffaac3aa050>
>>> f.fields['name']
<django.forms.fields.CharField object at 0x7ffaac6324d0>
You can alter the field and BoundField
of Form
instance to
change the way it is presented in the form:
>>> f.as_div().split("</div>")[0]
'<div><label for="id_subject">Subject:</label><input type="text" name="subject" maxlength="100" required id="id_subject">'
>>> f["subject"].label = "Topic"
>>> f.as_div().split("</div>")[0]
'<div><label for="id_subject">Topic:</label><input type="text" name="subject" maxlength="100" required id="id_subject">'
Beware not to alter the base_fields
attribute because this modification
will influence all subsequent ContactForm
instances within the same Python
process:
>>> f.base_fields["subject"].label_suffix = "?"
>>> another_f = CommentForm(auto_id=False)
>>> f.as_div().split("</div>")[0]
'<div><label for="id_subject">Subject?</label><input type="text" name="subject" maxlength="100" required id="id_subject">'
Accessing “clean” data¶
-
Form.
cleaned_data
¶
Each field in a Form
class is responsible not only for validating
data, but also for “cleaning” it – normalizing it to a consistent format. This
is a nice feature, because it allows data for a particular field to be input in
a variety of ways, always resulting in consistent output.
For example, DateField
normalizes input into a
Python datetime.date
object. Regardless of whether you pass it a string in
the format '1994-07-15'
, a datetime.date
object, or a number of other
formats, DateField
will always normalize it to a datetime.date
object
as long as it’s valid.
Once you’ve created a Form
instance with a set of data and validated
it, you can access the clean data via its cleaned_data
attribute:
>>> data = {'subject': 'hello',
... 'message': 'Hi there',
... 'sender': 'foo@example.com',
... 'cc_myself': True}
>>> f = ContactForm(data)
>>> f.is_valid()
True
>>> f.cleaned_data
{'cc_myself': True, 'message': 'Hi there', 'sender': 'foo@example.com', 'subject': 'hello'}
Note that any text-based field – such as CharField
or EmailField
–
always cleans the input into a string. We’ll cover the encoding implications
later in this document.
If your data does not validate, the cleaned_data
dictionary contains
only the valid fields:
>>> data = {'subject': '',
... 'message': 'Hi there',
... 'sender': 'invalid email address',
... 'cc_myself': True}
>>> f = ContactForm(data)
>>> f.is_valid()
False
>>> f.cleaned_data
{'cc_myself': True, 'message': 'Hi there'}
cleaned_data
will always only contain a key for fields defined in the
Form
, even if you pass extra data when you define the Form
. In this
example, we pass a bunch of extra fields to the ContactForm
constructor,
but cleaned_data
contains only the form’s fields:
>>> data = {'subject': 'hello',
... 'message': 'Hi there',
... 'sender': 'foo@example.com',
... 'cc_myself': True,
... 'extra_field_1': 'foo',
... 'extra_field_2': 'bar',
... 'extra_field_3': 'baz'}
>>> f = ContactForm(data)
>>> f.is_valid()
True
>>> f.cleaned_data # Doesn't contain extra_field_1, etc.
{'cc_myself': True, 'message': 'Hi there', 'sender': 'foo@example.com', 'subject': 'hello'}
When the Form
is valid, cleaned_data
will include a key and value for
all its fields, even if the data didn’t include a value for some optional
fields. In this example, the data dictionary doesn’t include a value for the
nick_name
field, but cleaned_data
includes it, with an empty value:
>>> from django import forms
>>> class OptionalPersonForm(forms.Form):
... first_name = forms.CharField()
... last_name = forms.CharField()
... nick_name = forms.CharField(required=False)
>>> data = {'first_name': 'John', 'last_name': 'Lennon'}
>>> f = OptionalPersonForm(data)
>>> f.is_valid()
True
>>> f.cleaned_data
{'nick_name': '', 'first_name': 'John', 'last_name': 'Lennon'}
In this above example, the cleaned_data
value for nick_name
is set to an
empty string, because nick_name
is CharField
, and CharField
s treat
empty values as an empty string. Each field type knows what its “blank” value
is – e.g., for DateField
, it’s None
instead of the empty string. For
full details on each field’s behavior in this case, see the “Empty value” note
for each field in the “Built-in Field
classes” section below.
You can write code to perform validation for particular form fields (based on their name) or for the form as a whole (considering combinations of various fields). More information about this is in Form and field validation.
Outputting forms as HTML¶
The second task of a Form
object is to render itself as HTML. To do so,
print
it:
>>> f = ContactForm()
>>> print(f)
<tr><th><label for="id_subject">Subject:</label></th><td><input id="id_subject" type="text" name="subject" maxlength="100" required></td></tr>
<tr><th><label for="id_message">Message:</label></th><td><input type="text" name="message" id="id_message" required></td></tr>
<tr><th><label for="id_sender">Sender:</label></th><td><input type="email" name="sender" id="id_sender" required></td></tr>
<tr><th><label for="id_cc_myself">Cc myself:</label></th><td><input type="checkbox" name="cc_myself" id="id_cc_myself"></td></tr>
If the form is bound to data, the HTML output will include that data
appropriately. For example, if a field is represented by an
<input type="text">
, the data will be in the value
attribute. If a
field is represented by an <input type="checkbox">
, then that HTML will
include checked
if appropriate:
>>> data = {'subject': 'hello',
... 'message': 'Hi there',
... 'sender': 'foo@example.com',
... 'cc_myself': True}
>>> f = ContactForm(data)
>>> print(f)
<tr><th><label for="id_subject">Subject:</label></th><td><input id="id_subject" type="text" name="subject" maxlength="100" value="hello" required></td></tr>
<tr><th><label for="id_message">Message:</label></th><td><input type="text" name="message" id="id_message" value="Hi there" required></td></tr>
<tr><th><label for="id_sender">Sender:</label></th><td><input type="email" name="sender" id="id_sender" value="foo@example.com" required></td></tr>
<tr><th><label for="id_cc_myself">Cc myself:</label></th><td><input type="checkbox" name="cc_myself" id="id_cc_myself" checked></td></tr>
This default output is a two-column HTML table, with a <tr>
for each field.
Notice the following:
- For flexibility, the output does not include the
<table>
and</table>
tags, nor does it include the<form>
and</form>
tags or an<input type="submit">
tag. It’s your job to do that. - Each field type has a default HTML representation.
CharField
is represented by an<input type="text">
andEmailField
by an<input type="email">
.BooleanField(null=False)
is represented by an<input type="checkbox">
. Note these are merely sensible defaults; you can specify which HTML to use for a given field by using widgets, which we’ll explain shortly. - The HTML
name
for each tag is taken directly from its attribute name in theContactForm
class. - The text label for each field – e.g.
'Subject:'
,'Message:'
and'Cc myself:'
is generated from the field name by converting all underscores to spaces and upper-casing the first letter. Again, note these are merely sensible defaults; you can also specify labels manually. - Each text label is surrounded in an HTML
<label>
tag, which points to the appropriate form field via itsid
. Itsid
, in turn, is generated by prepending'id_'
to the field name. Theid
attributes and<label>
tags are included in the output by default, to follow best practices, but you can change that behavior. - The output uses HTML5 syntax, targeting
<!DOCTYPE html>
. For example, it uses boolean attributes such aschecked
rather than the XHTML style ofchecked='checked'
.
Although <table>
output is the default output style when you print
a
form, other output styles are available. Each style is available as a method on
a form object, and each rendering method returns a string.
Default rendering¶
The default rendering when you print
a form uses the following methods and
attributes.
template_name
¶
-
Form.
template_name
¶
The name of the template rendered if the form is cast into a string, e.g. via
print(form)
or in a template via {{ form }}
.
By default, a property returning the value of the renderer’s
form_template_name
. You may set it
as a string template name in order to override that for a particular form
class.
In older versions template_name
defaulted to the string value
'django/forms/default.html'
.
render()
¶
-
Form.
render
(template_name=None, context=None, renderer=None)¶
The render method is called by __str__
as well as the
Form.as_table()
, Form.as_p()
, and Form.as_ul()
methods.
All arguments are optional and default to:
template_name
:Form.template_name
context
: Value returned byForm.get_context()
renderer
: Value returned byForm.default_renderer
By passing template_name
you can customize the template used for just a
single call.
get_context()
¶
-
Form.
get_context
()¶
Return the template context for rendering the form.
The available context is:
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.
template_name_label
¶
-
Form.
template_name_label
¶
The template used to render a field’s <label>
, used when calling
BoundField.label_tag()
/legend_tag()
. Can be changed per
form by overriding this attribute or more generally by overriding the default
template, see also Overriding built-in form templates.
Output styles¶
As well as rendering the form directly, such as in a template with
{{ form }}
, the following helper functions serve as a proxy to
Form.render()
passing a particular template_name
value.
These helpers are most useful in a template, where you need to override the
form renderer or form provided value but cannot pass the additional parameter
to render()
. For example, you can render a form as an unordered
list using {{ form.as_ul }}
.
Each helper pairs a form method with an attribute giving the appropriate template name.
as_div()
¶
-
Form.
template_name_div
¶
The template used by as_div()
. Default: 'django/forms/div.html'
.
-
Form.
as_div
()¶
as_div()
renders the form as a series of <div>
elements, with each
<div>
containing one field, such as:
>>> f = ContactForm()
>>> f.as_div()
… gives HTML like:
<div>
<label for="id_subject">Subject:</label>
<input type="text" name="subject" maxlength="100" required id="id_subject">
</div>
<div>
<label for="id_message">Message:</label>
<input type="text" name="message" required id="id_message">
</div>
<div>
<label for="id_sender">Sender:</label>
<input type="email" name="sender" required id="id_sender">
</div>
<div>
<label for="id_cc_myself">Cc myself:</label>
<input type="checkbox" name="cc_myself" id="id_cc_myself">
</div>
Note
Of the framework provided templates and output styles, as_div()
is
recommended over the as_p()
, as_table()
, and as_ul()
versions
as the template implements <fieldset>
and <legend>
to group related
inputs and is easier for screen reader users to navigate.
as_p()
¶
-
Form.
template_name_p
¶
The template used by as_p()
. Default: 'django/forms/p.html'
.
-
Form.
as_p
()¶
as_p()
renders the form as a series of <p>
tags, with each <p>
containing one field:
>>> f = ContactForm()
>>> f.as_p()
'<p><label for="id_subject">Subject:</label> <input id="id_subject" type="text" name="subject" maxlength="100" required></p>\n<p><label for="id_message">Message:</label> <input type="text" name="message" id="id_message" required></p>\n<p><label for="id_sender">Sender:</label> <input type="text" name="sender" id="id_sender" required></p>\n<p><label for="id_cc_myself">Cc myself:</label> <input type="checkbox" name="cc_myself" id="id_cc_myself"></p>'
>>> print(f.as_p())
<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> <input type="text" name="message" id="id_message" required></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>
as_ul()
¶
-
Form.
template_name_ul
¶
The template used by as_ul()
. Default: 'django/forms/ul.html'
.
-
Form.
as_ul
()¶
as_ul()
renders the form as a series of <li>
tags, with each <li>
containing one field. It does not include the <ul>
or </ul>
, so that
you can specify any HTML attributes on the <ul>
for flexibility:
>>> f = ContactForm()
>>> f.as_ul()
'<li><label for="id_subject">Subject:</label> <input id="id_subject" type="text" name="subject" maxlength="100" required></li>\n<li><label for="id_message">Message:</label> <input type="text" name="message" id="id_message" required></li>\n<li><label for="id_sender">Sender:</label> <input type="email" name="sender" id="id_sender" required></li>\n<li><label for="id_cc_myself">Cc myself:</label> <input type="checkbox" name="cc_myself" id="id_cc_myself"></li>'
>>> print(f.as_ul())
<li><label for="id_subject">Subject:</label> <input id="id_subject" type="text" name="subject" maxlength="100" required></li>
<li><label for="id_message">Message:</label> <input type="text" name="message" id="id_message" required></li>
<li><label for="id_sender">Sender:</label> <input type="email" name="sender" id="id_sender" required></li>
<li><label for="id_cc_myself">Cc myself:</label> <input type="checkbox" name="cc_myself" id="id_cc_myself"></li>
as_table()
¶
-
Form.
template_name_table
¶
The template used by as_table()
. Default: 'django/forms/table.html'
.
-
Form.
as_table
()¶
as_table()
renders the form as an HTML <table>
:
>>> f = ContactForm()
>>> f.as_table()
'<tr><th><label for="id_subject">Subject:</label></th><td><input id="id_subject" type="text" name="subject" maxlength="100" required></td></tr>\n<tr><th><label for="id_message">Message:</label></th><td><input type="text" name="message" id="id_message" required></td></tr>\n<tr><th><label for="id_sender">Sender:</label></th><td><input type="email" name="sender" id="id_sender" required></td></tr>\n<tr><th><label for="id_cc_myself">Cc myself:</label></th><td><input type="checkbox" name="cc_myself" id="id_cc_myself"></td></tr>'
>>> print(f)
<tr><th><label for="id_subject">Subject:</label></th><td><input id="id_subject" type="text" name="subject" maxlength="100" required></td></tr>
<tr><th><label for="id_message">Message:</label></th><td><input type="text" name="message" id="id_message" required></td></tr>
<tr><th><label for="id_sender">Sender:</label></th><td><input type="email" name="sender" id="id_sender" required></td></tr>
<tr><th><label for="id_cc_myself">Cc myself:</label></th><td><input type="checkbox" name="cc_myself" id="id_cc_myself"></td></tr>
Styling required or erroneous form rows¶
-
Form.
error_css_class
¶
-
Form.
required_css_class
¶
It’s pretty common to style form rows and fields that are required or have errors. For example, you might want to present required form rows in bold and highlight errors in red.
The Form
class has a couple of hooks you can use to add class
attributes to required rows or to rows with errors: set the
Form.error_css_class
and/or Form.required_css_class
attributes:
from django import forms
class ContactForm(forms.Form):
error_css_class = 'error'
required_css_class = 'required'
# ... and the rest of your fields here
Once you’ve done that, rows will be given "error"
and/or "required"
classes, as needed. The HTML will look something like:
>>> f = ContactForm(data)
>>> print(f.as_table())
<tr class="required"><th><label class="required" for="id_subject">Subject:</label> ...
<tr class="required"><th><label class="required" for="id_message">Message:</label> ...
<tr class="required error"><th><label class="required" for="id_sender">Sender:</label> ...
<tr><th><label for="id_cc_myself">Cc myself:<label> ...
>>> f['subject'].label_tag()
<label class="required" for="id_subject">Subject:</label>
>>> f['subject'].legend_tag()
<legend class="required" for="id_subject">Subject:</legend>
>>> f['subject'].label_tag(attrs={'class': 'foo'})
<label for="id_subject" class="foo required">Subject:</label>
>>> f['subject'].legend_tag(attrs={'class': 'foo'})
<legend for="id_subject" class="foo required">Subject:</legend>
Configuring form elements’ HTML id
attributes and <label>
tags¶
-
Form.
auto_id
¶
By default, the form rendering methods include:
- HTML
id
attributes on the form elements. - The corresponding
<label>
tags around the labels. An HTML<label>
tag designates which label text is associated with which form element. This small enhancement makes forms more usable and more accessible to assistive devices. It’s always a good idea to use<label>
tags.
The id
attribute values are generated by prepending id_
to the form
field names. This behavior is configurable, though, if you want to change the
id
convention or remove HTML id
attributes and <label>
tags
entirely.
Use the auto_id
argument to the Form
constructor to control the id
and label behavior. This argument must be True
, False
or a string.
If auto_id
is False
, then the form output will not include <label>
tags nor id
attributes:
>>> f = ContactForm(auto_id=False)
>>> print(f.as_div())
<div>Subject:<input type="text" name="subject" maxlength="100" required></div>
<div>Message:<textarea name="message" cols="40" rows="10" required></textarea></div>
<div>Sender:<input type="email" name="sender" required></div>
<div>Cc myself:<input type="checkbox" name="cc_myself"></div>
If auto_id
is set to True
, then the form output will include
<label>
tags and will use the field name as its id
for each form
field:
>>> f = ContactForm(auto_id=True)
>>> print(f.as_div())
<div><label for="subject">Subject:</label><input type="text" name="subject" maxlength="100" required id="subject"></div>
<div><label for="message">Message:</label><textarea name="message" cols="40" rows="10" required id="message"></textarea></div>
<div><label for="sender">Sender:</label><input type="email" name="sender" required id="sender"></div>
<div><label for="cc_myself">Cc myself:</label><input type="checkbox" name="cc_myself" id="cc_myself"></div>
If auto_id
is set to a string containing the format character '%s'
,
then the form output will include <label>
tags, and will generate id
attributes based on the format string. For example, for a format string
'field_%s'
, a field named subject
will get the id
value
'field_subject'
. Continuing our example:
>>> f = ContactForm(auto_id='id_for_%s')
>>> print(f.as_div())
<div><label for="id_for_subject">Subject:</label><input type="text" name="subject" maxlength="100" required id="id_for_subject"></div>
<div><label for="id_for_message">Message:</label><textarea name="message" cols="40" rows="10" required id="id_for_message"></textarea></div>
<div><label for="id_for_sender">Sender:</label><input type="email" name="sender" required id="id_for_sender"></div>
<div><label for="id_for_cc_myself">Cc myself:</label><input type="checkbox" name="cc_myself" id="id_for_cc_myself"></div>
If auto_id
is set to any other true value – such as a string that doesn’t
include %s
– then the library will act as if auto_id
is True
.
By default, auto_id
is set to the string 'id_%s'
.
-
Form.
label_suffix
¶
A translatable string (defaults to a colon (:
) in English) that will be
appended after any label name when a form is rendered.
It’s possible to customize that character, or omit it entirely, using the
label_suffix
parameter:
>>> f = ContactForm(auto_id='id_for_%s', label_suffix='')
>>> print(f.as_div())
<div><label for="id_for_subject">Subject</label><input type="text" name="subject" maxlength="100" required id="id_for_subject"></div>
<div><label for="id_for_message">Message</label><textarea name="message" cols="40" rows="10" required id="id_for_message"></textarea></div>
<div><label for="id_for_sender">Sender</label><input type="email" name="sender" required id="id_for_sender"></div>
<div><label for="id_for_cc_myself">Cc myself</label><input type="checkbox" name="cc_myself" id="id_for_cc_myself"></div>
>>> f = ContactForm(auto_id='id_for_%s', label_suffix=' ->')
>>> print(f.as_div())
<div><label for="id_for_subject">Subject:</label><input type="text" name="subject" maxlength="100" required id="id_for_subject"></div>
<div><label for="id_for_message">Message -></label><textarea name="message" cols="40" rows="10" required id="id_for_message"></textarea></div>
<div><label for="id_for_sender">Sender -></label><input type="email" name="sender" required id="id_for_sender"></div>
<div><label for="id_for_cc_myself">Cc myself -></label><input type="checkbox" name="cc_myself" id="id_for_cc_myself"></div>
Note that the label suffix is added only if the last character of the
label isn’t a punctuation character (in English, those are .
, !
, ?
or :
).
Fields can also define their own label_suffix
.
This will take precedence over Form.label_suffix
. The suffix can also be overridden at runtime
using the label_suffix
parameter to
label_tag()
/
legend_tag()
.
-
Form.
use_required_attribute
¶
When set to True
(the default), required form fields will have the
required
HTML attribute.
Formsets instantiate forms with
use_required_attribute=False
to avoid incorrect browser validation when
adding and deleting forms from a formset.
Configuring the rendering of a form’s widgets¶
-
Form.
default_renderer
¶
Specifies the renderer to use for the form. Defaults to
None
which means to use the default renderer specified by the
FORM_RENDERER
setting.
You can set this as a class attribute when declaring your form or use the
renderer
argument to Form.__init__()
. For example:
from django import forms
class MyForm(forms.Form):
default_renderer = MyRenderer()
or:
form = MyForm(renderer=MyRenderer())
Notes on field ordering¶
In the as_p()
, as_ul()
and as_table()
shortcuts, the fields are
displayed in the order in which you define them in your form class. For
example, in the ContactForm
example, the fields are defined in the order
subject
, message
, sender
, cc_myself
. To reorder the HTML
output, change the order in which those fields are listed in the class.
There are several other ways to customize the order:
-
Form.
field_order
¶
By default Form.field_order=None
, which retains the order in which you
define the fields in your form class. If field_order
is a list of field
names, the fields are ordered as specified by the list and remaining fields are
appended according to the default order. Unknown field names in the list are
ignored. This makes it possible to disable a field in a subclass by setting it
to None
without having to redefine ordering.
You can also use the Form.field_order
argument to a Form
to
override the field order. If a Form
defines
field_order
and you include field_order
when instantiating
the Form
, then the latter field_order
will have precedence.
-
Form.
order_fields
(field_order)¶
You may rearrange the fields any time using order_fields()
with a list of
field names as in field_order
.
How errors are displayed¶
If you render a bound Form
object, the act of rendering will automatically
run the form’s validation if it hasn’t already happened, and the HTML output
will include the validation errors as a <ul class="errorlist">
near the
field. The particular positioning of the error messages depends on the output
method you’re using:
>>> data = {'subject': '',
... 'message': 'Hi there',
... 'sender': 'invalid email address',
... 'cc_myself': True}
>>> f = ContactForm(data, auto_id=False)
>>> print(f.as_div())
<div>Subject:<ul class="errorlist"><li>This field is required.</li></ul><input type="text" name="subject" maxlength="100" required></div>
<div>Message:<textarea name="message" cols="40" rows="10" required>Hi there</textarea></div>
<div>Sender:<ul class="errorlist"><li>Enter a valid email address.</li></ul><input type="email" name="sender" value="invalid email address" required></div>
<div>Cc myself:<input type="checkbox" name="cc_myself" checked></div>
>>> print(f.as_table())
<tr><th>Subject:</th><td><ul class="errorlist"><li>This field is required.</li></ul><input type="text" name="subject" maxlength="100" required></td></tr>
<tr><th>Message:</th><td><textarea name="message" cols="40" rows="10" required></textarea></td></tr>
<tr><th>Sender:</th><td><ul class="errorlist"><li>Enter a valid email address.</li></ul><input type="email" name="sender" value="invalid email address" required></td></tr>
<tr><th>Cc myself:</th><td><input checked type="checkbox" name="cc_myself"></td></tr>
>>> print(f.as_ul())
<li><ul class="errorlist"><li>This field is required.</li></ul>Subject: <input type="text" name="subject" maxlength="100" required></li>
<li>Message: <textarea name="message" cols="40" rows="10" required></textarea></li>
<li><ul class="errorlist"><li>Enter a valid email address.</li></ul>Sender: <input type="email" name="sender" value="invalid email address" required></li>
<li>Cc myself: <input checked type="checkbox" name="cc_myself"></li>
>>> print(f.as_p())
<p><ul class="errorlist"><li>This field is required.</li></ul></p>
<p>Subject: <input type="text" name="subject" maxlength="100" required></p>
<p>Message: <textarea name="message" cols="40" rows="10" required></textarea></p>
<p><ul class="errorlist"><li>Enter a valid email address.</li></ul></p>
<p>Sender: <input type="email" name="sender" value="invalid email address" required></p>
<p>Cc myself: <input checked type="checkbox" name="cc_myself"></p>
Customizing the error list format¶
-
class
ErrorList
(initlist=None, error_class=None, renderer=None)¶ By default, forms use
django.forms.utils.ErrorList
to format validation errors.ErrorList
is a list like object whereinitlist
is the list of errors. In addition this class has the following attributes and methods.-
error_class
¶ The CSS classes to be used when rendering the error list. Any provided classes are added to the default
errorlist
class.
-
renderer
¶ Specifies the renderer to use for
ErrorList
. Defaults toNone
which means to use the default renderer specified by theFORM_RENDERER
setting.
-
template_name
¶ The name of the template used when calling
__str__
orrender()
. By default this is'django/forms/errors/list/default.html'
which is a proxy for the'ul.html'
template.
-
template_name_text
¶ The name of the template used when calling
as_text()
. By default this is'django/forms/errors/list/text.html'
. This template renders the errors as a list of bullet points.
-
template_name_ul
¶ The name of the template used when calling
as_ul()
. By default this is'django/forms/errors/list/ul.html'
. This template renders the errors in<li>
tags with a wrapping<ul>
with the CSS classes as defined byerror_class
.
-
get_context
()¶ Return context for rendering of errors in a template.
The available context is:
errors
: A list of the errors.error_class
: A string of CSS classes.
-
render
(template_name=None, context=None, renderer=None)¶ The render method is called by
__str__
as well as by theas_ul()
method.All arguments are optional and will default to:
template_name
: Value returned bytemplate_name
context
: Value returned byget_context()
renderer
: Value returned byrenderer
-
as_text
()¶ Renders the error list using the template defined by
template_name_text
.
-
as_ul
()¶ Renders the error list using the template defined by
template_name_ul
.
If you’d like to customize the rendering of errors this can be achieved by overriding the
template_name
attribute or more generally by overriding the default template, see also Overriding built-in form templates.-
Deprecated since version 4.0: The ability to return a str
when calling the __str__
method is
deprecated. Use the template engine instead which returns a SafeString
.
More granular output¶
The as_p()
, as_ul()
, and as_table()
methods are shortcuts –
they’re not the only way a form object can be displayed.
-
class
BoundField
[source]¶ Used to display HTML or access attributes for a single field of a
Form
instance.The
__str__()
method of this object displays the HTML for this field.
To retrieve a single BoundField
, use dictionary lookup syntax on your form
using the field’s name as the key:
>>> form = ContactForm()
>>> print(form['subject'])
<input id="id_subject" type="text" name="subject" maxlength="100" required>
To retrieve all BoundField
objects, iterate the form:
>>> form = ContactForm()
>>> for boundfield in form: print(boundfield)
<input id="id_subject" type="text" name="subject" maxlength="100" required>
<input type="text" name="message" id="id_message" required>
<input type="email" name="sender" id="id_sender" required>
<input type="checkbox" name="cc_myself" id="id_cc_myself">
The field-specific output honors the form object’s auto_id
setting:
>>> f = ContactForm(auto_id=False)
>>> print(f['message'])
<input type="text" name="message" required>
>>> f = ContactForm(auto_id='id_%s')
>>> print(f['message'])
<input type="text" name="message" id="id_message" required>
Attributes of BoundField
¶
-
BoundField.
auto_id
¶ The HTML ID attribute for this
BoundField
. Returns an empty string ifForm.auto_id
isFalse
.
-
BoundField.
data
¶ This property returns the data for this
BoundField
extracted by the widget’svalue_from_datadict()
method, orNone
if it wasn’t given:>>> unbound_form = ContactForm() >>> print(unbound_form['subject'].data) None >>> bound_form = ContactForm(data={'subject': 'My Subject'}) >>> print(bound_form['subject'].data) My Subject
-
BoundField.
errors
¶ A list-like object that is displayed as an HTML
<ul class="errorlist">
when printed:>>> data = {'subject': 'hi', 'message': '', 'sender': '', 'cc_myself': ''} >>> f = ContactForm(data, auto_id=False) >>> print(f['message']) <input type="text" name="message" required> >>> f['message'].errors ['This field is required.'] >>> print(f['message'].errors) <ul class="errorlist"><li>This field is required.</li></ul> >>> f['subject'].errors [] >>> print(f['subject'].errors) >>> str(f['subject'].errors) ''
-
BoundField.
field
¶ The form
Field
instance from the form class that thisBoundField
wraps.
-
BoundField.
form
¶ The
Form
instance thisBoundField
is bound to.
-
BoundField.
html_name
¶ The name that will be used in the widget’s HTML
name
attribute. It takes the formprefix
into account.
-
BoundField.
id_for_label
¶ Use this property to render the ID of this field. For example, if you are manually constructing a
<label>
in your template (despite the fact thatlabel_tag()
/legend_tag()
will do this for you):<label for="{{ form.my_field.id_for_label }}">...</label>{{ my_field }}
By default, this will be the field’s name prefixed by
id_
(”id_my_field
” for the example above). You may modify the ID by settingattrs
on the field’s widget. For example, declaring a field like this:my_field = forms.CharField(widget=forms.TextInput(attrs={'id': 'myFIELD'}))
and using the template above, would render something like:
<label for="myFIELD">...</label><input id="myFIELD" type="text" name="my_field" required>
-
BoundField.
initial
¶ Use
BoundField.initial
to retrieve initial data for a form field. It retrieves the data fromForm.initial
if present, otherwise tryingField.initial
. Callable values are evaluated. See Initial form values for more examples.BoundField.initial
caches its return value, which is useful especially when dealing with callables whose return values can change (e.g.datetime.now
oruuid.uuid4
):>>> from datetime import datetime >>> class DatedCommentForm(CommentForm): ... created = forms.DateTimeField(initial=datetime.now) >>> f = DatedCommentForm() >>> f['created'].initial datetime.datetime(2021, 7, 27, 9, 5, 54) >>> f['created'].initial datetime.datetime(2021, 7, 27, 9, 5, 54)
Using
BoundField.initial
is recommended overget_initial_for_field()
.
Returns
True
if thisBoundField
’s widget is hidden.
-
BoundField.
label
¶ The
label
of the field. This is used inlabel_tag()
/legend_tag()
.
-
BoundField.
name
¶ The name of this field in the form:
>>> f = ContactForm() >>> print(f['subject'].name) subject >>> print(f['message'].name) message
-
BoundField.
use_fieldset
¶ - New in Django Development version.
Returns the value of this BoundField widget’s
use_fieldset
attribute.
-
BoundField.
widget_type
¶ Returns the lowercased class name of the wrapped field’s widget, with any trailing
input
orwidget
removed. This may be used when building forms where the layout is dependent upon the widget type. For example:{% for field in form %} {% if field.widget_type == 'checkbox' %} # render one way {% else %} # render another way {% endif %} {% endfor %}
Methods of BoundField
¶
Returns a string of HTML for representing this as an
<input type="hidden">
.**kwargs
are passed toas_widget()
.This method is primarily used internally. You should use a widget instead.
-
BoundField.
as_widget
(widget=None, attrs=None, only_initial=False)[source]¶ Renders the field by rendering the passed widget, adding any HTML attributes passed as
attrs
. If no widget is specified, then the field’s default widget will be used.only_initial
is used by Django internals and should not be set explicitly.
-
BoundField.
css_classes
(extra_classes=None)[source]¶ When you use Django’s rendering shortcuts, CSS classes are used to indicate required form fields or fields that contain errors. If you’re manually rendering a form, you can access these CSS classes using the
css_classes
method:>>> f = ContactForm(data={'message': ''}) >>> f['message'].css_classes() 'required'
If you want to provide some additional classes in addition to the error and required classes that may be required, you can provide those classes as an argument:
>>> f = ContactForm(data={'message': ''}) >>> f['message'].css_classes('foo bar') 'foo bar required'
-
BoundField.
label_tag
(contents=None, attrs=None, label_suffix=None, tag=None)[source]¶ Renders a label tag for the form field using the template specified by
Form.template_name_label
.The available context is:
field
: This instance of theBoundField
.contents
: By default a concatenated string ofBoundField.label
andForm.label_suffix
(orField.label_suffix
, if set). This can be overridden by thecontents
andlabel_suffix
arguments.attrs
: Adict
containingfor
,Form.required_css_class
, andid
.id
is generated by the field’s widgetattrs
orBoundField.auto_id
. Additional attributes can be provided by theattrs
argument.use_tag
: A boolean which isTrue
if the label has anid
. IfFalse
the default template omits thetag
.tag
: An optional string to customize the tag, defaults tolabel
.
Tip
In your template
field
is the instance of theBoundField
. Thereforefield.field
accessesBoundField.field
being the field you declare, e.g.forms.CharField
.To separately render the label tag of a form field, you can call its
label_tag()
method:>>> f = ContactForm(data={'message': ''}) >>> print(f['message'].label_tag()) <label for="id_message">Message:</label>
If you’d like to customize the rendering this can be achieved by overriding the
Form.template_name_label
attribute or more generally by overriding the default template, see also Overriding built-in form templates.Changed in Django Development version:The
tag
argument was added.
-
BoundField.
legend_tag
(contents=None, attrs=None, label_suffix=None)¶ - New in Django Development version.
Calls
label_tag()
withtag='legend'
to render the label with<legend>
tags. This is useful when rendering radio and multiple checkbox widgets where<legend>
may be more appropriate than a<label>
.
-
BoundField.
value
()[source]¶ Use this method to render the raw value of this field as it would be rendered by a
Widget
:>>> initial = {'subject': 'welcome'} >>> unbound_form = ContactForm(initial=initial) >>> bound_form = ContactForm(data={'subject': 'hi'}, initial=initial) >>> print(unbound_form['subject'].value()) welcome >>> print(bound_form['subject'].value()) hi
Customizing BoundField
¶
If you need to access some additional information about a form field in a
template and using a subclass of Field
isn’t
sufficient, consider also customizing BoundField
.
A custom form field can override get_bound_field()
:
-
Field.
get_bound_field
(form, field_name)[source]¶ Takes an instance of
Form
and the name of the field. The return value will be used when accessing the field in a template. Most likely it will be an instance of a subclass ofBoundField
.
If you have a GPSCoordinatesField
, for example, and want to be able to
access additional information about the coordinates in a template, this could
be implemented as follows:
class GPSCoordinatesBoundField(BoundField):
@property
def country(self):
"""
Return the country the coordinates lie in or None if it can't be
determined.
"""
value = self.value()
if value:
return get_country_from_coordinates(value)
else:
return None
class GPSCoordinatesField(Field):
def get_bound_field(self, form, field_name):
return GPSCoordinatesBoundField(form, self, field_name)
Now you can access the country in a template with
{{ form.coordinates.country }}
.
Binding uploaded files to a form¶
Dealing with forms that have FileField
and ImageField
fields
is a little more complicated than a normal form.
Firstly, in order to upload files, you’ll need to make sure that your
<form>
element correctly defines the enctype
as
"multipart/form-data"
:
<form enctype="multipart/form-data" method="post" action="/foo/">
Secondly, when you use the form, you need to bind the file data. File
data is handled separately to normal form data, so when your form
contains a FileField
and ImageField
, you will need to specify
a second argument when you bind your form. So if we extend our
ContactForm to include an ImageField
called mugshot
, we
need to bind the file data containing the mugshot image:
# Bound form with an image field
>>> from django.core.files.uploadedfile import SimpleUploadedFile
>>> data = {'subject': 'hello',
... 'message': 'Hi there',
... 'sender': 'foo@example.com',
... 'cc_myself': True}
>>> file_data = {'mugshot': SimpleUploadedFile('face.jpg', <file data>)}
>>> f = ContactFormWithMugshot(data, file_data)
In practice, you will usually specify request.FILES
as the source
of file data (just like you use request.POST
as the source of
form data):
# Bound form with an image field, data from the request
>>> f = ContactFormWithMugshot(request.POST, request.FILES)
Constructing an unbound form is the same as always – omit both form data and file data:
# Unbound form with an image field
>>> f = ContactFormWithMugshot()
Testing for multipart forms¶
-
Form.
is_multipart
()¶
If you’re writing reusable views or templates, you may not know ahead of time
whether your form is a multipart form or not. The is_multipart()
method
tells you whether the form requires multipart encoding for submission:
>>> f = ContactFormWithMugshot()
>>> f.is_multipart()
True
Here’s an example of how you might use this in a template:
{% if form.is_multipart %}
<form enctype="multipart/form-data" method="post" action="/foo/">
{% else %}
<form method="post" action="/foo/">
{% endif %}
{{ form }}
</form>
Subclassing forms¶
If you have multiple Form
classes that share fields, you can use
subclassing to remove redundancy.
When you subclass a custom Form
class, the resulting subclass will
include all fields of the parent class(es), followed by the fields you define
in the subclass.
In this example, ContactFormWithPriority
contains all the fields from
ContactForm
, plus an additional field, priority
. The ContactForm
fields are ordered first:
>>> class ContactFormWithPriority(ContactForm):
... priority = forms.CharField()
>>> f = ContactFormWithPriority(auto_id=False)
>>> print(f.as_div())
<div>Subject:<input type="text" name="subject" maxlength="100" required></div>
<div>Message:<textarea name="message" cols="40" rows="10" required></textarea></div>
<div>Sender:<input type="email" name="sender" required></div>
<div>Cc myself:<input type="checkbox" name="cc_myself"></div>
<div>Priority:<input type="text" name="priority" required></div>
It’s possible to subclass multiple forms, treating forms as mixins. In this
example, BeatleForm
subclasses both PersonForm
and InstrumentForm
(in that order), and its field list includes the fields from the parent
classes:
>>> from django import forms
>>> class PersonForm(forms.Form):
... first_name = forms.CharField()
... last_name = forms.CharField()
>>> class InstrumentForm(forms.Form):
... instrument = forms.CharField()
>>> class BeatleForm(InstrumentForm, PersonForm):
... haircut_type = forms.CharField()
>>> b = BeatleForm(auto_id=False)
>>> print(b.as_div())
<div>First name:<input type="text" name="first_name" required></div>
<div>Last name:<input type="text" name="last_name" required></div>
<div>Instrument:<input type="text" name="instrument" required></div>
<div>Haircut type:<input type="text" name="haircut_type" required></div>
It’s possible to declaratively remove a Field
inherited from a parent class
by setting the name of the field to None
on the subclass. For example:
>>> from django import forms
>>> class ParentForm(forms.Form):
... name = forms.CharField()
... age = forms.IntegerField()
>>> class ChildForm(ParentForm):
... name = None
>>> list(ChildForm().fields)
['age']
Prefixes for forms¶
-
Form.
prefix
¶
You can put several Django forms inside one <form>
tag. To give each
Form
its own namespace, use the prefix
keyword argument:
>>> mother = PersonForm(prefix="mother")
>>> father = PersonForm(prefix="father")
>>> print(mother.as_div())
<div><label for="id_mother-first_name">First name:</label><input type="text" name="mother-first_name" required id="id_mother-first_name"></div>
<div><label for="id_mother-last_name">Last name:</label><input type="text" name="mother-last_name" required id="id_mother-last_name"></div>
>>> print(father.as_div())
<div><label for="id_father-first_name">First name:</label><input type="text" name="father-first_name" required id="id_father-first_name"></div>
<div><label for="id_father-last_name">Last name:</label><input type="text" name="father-last_name" required id="id_father-last_name"></div>
The prefix can also be specified on the form class:
>>> class PersonForm(forms.Form):
... ...
... prefix = 'person'