About this document
This document covers the gritty details of Django’s forms API. You should read the introduction to working with forms first.
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, simply 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.
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.
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.
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
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.
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.
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. It’s trivial to do so using a JavaScript library like jQuery - simply
use $(el).text(errorText) rather than .html().
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.
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().
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 simple 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.
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.
This method returns the list of errors from Form.errors that aren’t associated with a particular field.
This includes ValidationErrors that are raised in Form.clean() and errors added using Form.add_error(None,
"...").
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
{}
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>
Use get_initial_for_field() to retrieve initial data for a form
field. It retrieves data from Form.initial and Field.initial,
in that order, and evaluates any callable initial values.
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.
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']
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 of Form instance to change the way it is
presented in the form:
>>> f.as_table().split('\n')[0]
'<tr><th>Name:</th><td><input name="name" type="text" value="instance" required></td></tr>'
>>> f.fields['name'].label = "Username"
>>> f.as_table().split('\n')[0]
'<tr><th>Username:</th><td><input name="name" type="text" value="instance" required></td></tr>'
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['name'].label = "Username"
>>> another_f = CommentForm(auto_id=False)
>>> another_f.as_table().split('\n')[0]
'<tr><th>Username:</th><td><input name="name" type="text" value="class" required></td></tr>'
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 CharFields 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.
The second task of a Form object is to render itself as HTML. To do so,
simply 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"> and EmailField by an
<input type="email">.
BooleanField 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 the ContactForm 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 its id. Its id, in turn, is
generated by prepending 'id_' to the field name. The id
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 as checked rather than the XHTML style
of checked='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.
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()¶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()¶Finally, as_table() outputs the form as an HTML <table>. This is
exactly the same as print. In fact, when you print a form object,
it calls its as_table() method behind the scenes:
>>> 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>
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: simply 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'].label_tag(attrs={'class': 'foo'})
<label for="id_subject" class="foo required">Subject:</label>
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())
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, just change the order in which those fields are listed in the class.
There are several other ways to customize the 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.
You may rearrange the fields any time using order_fields() with a list of
field names as in field_order.
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_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><input type="text" name="message" value="Hi there" required></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: <input type="text" name="message" value="Hi there" required></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: <input type="text" name="message" value="Hi there" required></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>
By default, forms use django.forms.utils.ErrorList to format validation
errors. If you’d like to use an alternate class for displaying errors, you can
pass that in at construction time:
>>> from django.forms.utils import ErrorList
>>> class DivErrorList(ErrorList):
... def __str__(self):
... return self.as_divs()
... def as_divs(self):
... if not self: return ''
... return '<div class="errorlist">%s</div>' % ''.join(['<div class="error">%s</div>' % e for e in self])
>>> f = ContactForm(data, auto_id=False, error_class=DivErrorList)
>>> f.as_p()
<div class="errorlist"><div class="error">This field is required.</div></div>
<p>Subject: <input type="text" name="subject" maxlength="100" required></p>
<p>Message: <input type="text" name="message" value="Hi there" required></p>
<div class="errorlist"><div class="error">Enter a valid email address.</div></div>
<p>Sender: <input type="email" name="sender" value="invalid email address" required></p>
<p>Cc myself: <input checked type="checkbox" name="cc_myself"></p>
The as_p(), as_ul(), and as_table() methods are simply shortcuts –
they’re not the only way a form object can be displayed.
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>
BoundField¶The HTML ID attribute for this BoundField. Returns an empty string
if Form.auto_id is False.
This property returns the data for this BoundField
extracted by the widget’s value_from_datadict()
method, or None 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
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)
''
The form Field instance from the form class that
this BoundField wraps.
The Form instance this BoundField
is bound to.
The name that will be used in the widget’s HTML name attribute. It takes
the form prefix into account.
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 that
label_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 setting
attrs 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>
Returns True if this BoundField’s widget is
hidden.
The label of the field. This is used in
label_tag().
The name of this field in the form:
>>> f = ContactForm()
>>> print(f['subject'].name)
subject
>>> print(f['message'].name)
message
BoundField¶Returns a string of HTML for representing this as an <input type="hidden">.
**kwargs are passed to as_widget().
This method is primarily used internally. You should use a widget instead.
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.
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'
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>
You can provide the contents parameter which will replace the
auto-generated label tag. An attrs dictionary may contain additional
attributes for the <label> tag.
The HTML that’s generated includes the form’s
label_suffix (a colon, by default) or, if set, the
current field’s label_suffix. The optional
label_suffix parameter allows you to override any previously set
suffix. For example, you can use an empty string to hide the label on selected
fields. If you need to do this in a template, you could write a custom
filter to allow passing parameters to label_tag.
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
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():
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 of
BoundField.
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 }}.
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 – just omit both form data and file data:
# Unbound form with an image field
>>> f = ContactFormWithMugshot()
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>
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_ul())
<li>Subject: <input type="text" name="subject" maxlength="100" required></li>
<li>Message: <input type="text" name="message" required></li>
<li>Sender: <input type="email" name="sender" required></li>
<li>Cc myself: <input type="checkbox" name="cc_myself"></li>
<li>Priority: <input type="text" name="priority" required></li>
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_ul())
<li>First name: <input type="text" name="first_name" required></li>
<li>Last name: <input type="text" name="last_name" required></li>
<li>Instrument: <input type="text" name="instrument" required></li>
<li>Haircut type: <input type="text" name="haircut_type" required></li>
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']
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_ul())
<li><label for="id_mother-first_name">First name:</label> <input type="text" name="mother-first_name" id="id_mother-first_name" required></li>
<li><label for="id_mother-last_name">Last name:</label> <input type="text" name="mother-last_name" id="id_mother-last_name" required></li>
>>> print(father.as_ul())
<li><label for="id_father-first_name">First name:</label> <input type="text" name="father-first_name" id="id_father-first_name" required></li>
<li><label for="id_father-last_name">Last name:</label> <input type="text" name="father-last_name" id="id_father-last_name" required></li>
The prefix can also be specified on the form class:
>>> class PersonForm(forms.Form):
... ...
... prefix = 'person'
Dec 25, 2023