django1/docs/ref/forms/api.txt

689 lines
33 KiB
Plaintext

.. _ref-forms-api:
=============
The Forms API
=============
.. currentmodule:: django.forms
.. admonition:: About this document
This document covers the gritty details of Django's forms API. You should
read the :ref:`introduction to working with forms <topics-forms-index>`
first.
.. _ref-forms-api-bound-unbound:
Bound and unbound forms
-----------------------
A :class:`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 :class:`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 :class:`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 :class:`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 :class:`Field`, as we'll see
in a moment.
.. attribute:: Form.is_bound
If you need to distinguish between bound and unbound form instances at runtime,
check the value of the form's :attr:`~Form.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 :class:`Form` instance and want to change the data somehow,
or if you want to bind an unbound :class:`Form` instance to some data, create
another :class:`Form` instance. There is no way to change data in a
:class:`Form` instance. Once a :class:`Form` instance has been created, you
should consider its data immutable, whether it has data or not.
Using forms to validate data
----------------------------
.. method:: Form.is_valid()
The primary task of a :class:`Form` object is to validate data. With a bound
:class:`Form` instance, call the :meth:`~Form.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
e-mail address::
>>> data = {'subject': '',
... 'message': 'Hi there',
... 'sender': 'invalid e-mail address',
... 'cc_myself': True}
>>> f = ContactForm(data)
>>> f.is_valid()
False
.. attribute:: Form.errors
Access the :attr:`~Form.errors` attribute to get a dictionary of error
messages::
>>> f.errors
{'sender': [u'Enter a valid e-mail address.'], 'subject': [u'This field is required.']}
In this dictionary, the keys are the field names, and the values are lists of
Unicode strings representing the error messages. The error messages are stored
in lists because a field can have multiple error messages.
You can access :attr:`~Form.errors` without having to call
:meth:`~Form.is_valid` first. The form's data will be validated the first time
either you call :meth:`~Form.is_valid` or access :attr:`~Form.errors`.
The validation routines will only get called once, regardless of how many times
you access :attr:`~Form.errors` or call :meth:`~Form.is_valid`. This means that
if validation has side effects, those side effects will only be triggered once.
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
{}
Accessing "clean" 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 the ``cleaned_data`` attribute of the ``Form``
object::
>>> 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': u'Hi there', 'sender': u'foo@example.com', 'subject': u'hello'}
.. note::
**New in Django development version** The ``cleaned_data`` attribute was
called ``clean_data`` in earlier releases.
Note that any text-based field -- such as ``CharField`` or ``EmailField`` --
always cleans the input into a Unicode string. We'll cover the encoding
implications later in this document.
If your data does *not* validate, your ``Form`` instance will not have a
``cleaned_data`` attribute::
>>> data = {'subject': '',
... 'message': 'Hi there',
... 'sender': 'invalid e-mail address',
... 'cc_myself': True}
>>> f = ContactForm(data)
>>> f.is_valid()
False
>>> f.cleaned_data
Traceback (most recent call last):
...
AttributeError: 'ContactForm' object has no attribute 'cleaned_data'
``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': u'Hi there', 'sender': u'foo@example.com', 'subject': u'hello'}
``cleaned_data`` will include a key and value for *all* fields defined in the
``Form``, even if the data didn't include a value for fields that are not
required. 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::
>>> class OptionalPersonForm(Form):
... first_name = CharField()
... last_name = CharField()
... nick_name = CharField(required=False)
>>> data = {'first_name': u'John', 'last_name': u'Lennon'}
>>> f = OptionalPersonForm(data)
>>> f.is_valid()
True
>>> f.cleaned_data
{'nick_name': u'', 'first_name': u'John', 'last_name': u'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 :ref:`ref-forms-validation`.
Outputting forms as HTML
------------------------
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" /></td></tr>
<tr><th><label for="id_message">Message:</label></th><td><input type="text" name="message" id="id_message" /></td></tr>
<tr><th><label for="id_sender">Sender:</label></th><td><input type="text" name="sender" id="id_sender" /></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="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" /></td></tr>
<tr><th><label for="id_message">Message:</label></th><td><input type="text" name="message" id="id_message" value="Hi there" /></td></tr>
<tr><th><label for="id_sender">Sender:</label></th><td><input type="text" name="sender" id="id_sender" value="foo@example.com" /></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="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`` and
``EmailField`` are represented by an ``<input type="text">``.
``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.
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 Unicode object.
``as_p()``
~~~~~~~~~~
``Form.as_p()`` renders the form as a series of ``<p>`` tags, with each ``<p>``
containing one field::
>>> f = ContactForm()
>>> f.as_p()
u'<p><label for="id_subject">Subject:</label> <input id="id_subject" type="text" name="subject" maxlength="100" /></p>\n<p><label for="id_message">Message:</label> <input type="text" name="message" id="id_message" /></p>\n<p><label for="id_sender">Sender:</label> <input type="text" name="sender" id="id_sender" /></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" /></p>
<p><label for="id_message">Message:</label> <input type="text" name="message" id="id_message" /></p>
<p><label for="id_sender">Sender:</label> <input type="text" name="sender" id="id_sender" /></p>
<p><label for="id_cc_myself">Cc myself:</label> <input type="checkbox" name="cc_myself" id="id_cc_myself" /></p>
``as_ul()``
~~~~~~~~~~~
``Form.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()
u'<li><label for="id_subject">Subject:</label> <input id="id_subject" type="text" name="subject" maxlength="100" /></li>\n<li><label for="id_message">Message:</label> <input type="text" name="message" id="id_message" /></li>\n<li><label for="id_sender">Sender:</label> <input type="text" name="sender" id="id_sender" /></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" /></li>
<li><label for="id_message">Message:</label> <input type="text" name="message" id="id_message" /></li>
<li><label for="id_sender">Sender:</label> <input type="text" name="sender" id="id_sender" /></li>
<li><label for="id_cc_myself">Cc myself:</label> <input type="checkbox" name="cc_myself" id="id_cc_myself" /></li>
``as_table()``
~~~~~~~~~~~~~~
Finally, ``Form.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()
u'<tr><th><label for="id_subject">Subject:</label></th><td><input id="id_subject" type="text" name="subject" maxlength="100" /></td></tr>\n<tr><th><label for="id_message">Message:</label></th><td><input type="text" name="message" id="id_message" /></td></tr>\n<tr><th><label for="id_sender">Sender:</label></th><td><input type="text" name="sender" id="id_sender" /></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.as_table()
<tr><th><label for="id_subject">Subject:</label></th><td><input id="id_subject" type="text" name="subject" maxlength="100" /></td></tr>
<tr><th><label for="id_message">Message:</label></th><td><input type="text" name="message" id="id_message" /></td></tr>
<tr><th><label for="id_sender">Sender:</label></th><td><input type="text" name="sender" id="id_sender" /></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>
.. _ref-forms-api-configuring-label:
Configuring HTML ``<label>`` tags
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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.
By default, the form rendering methods include HTML ``id`` attributes on the
form elements and corresponding ``<label>`` tags around the labels. 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 label
and ``id`` 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_table()
<tr><th>Subject:</th><td><input type="text" name="subject" maxlength="100" /></td></tr>
<tr><th>Message:</th><td><input type="text" name="message" /></td></tr>
<tr><th>Sender:</th><td><input type="text" name="sender" /></td></tr>
<tr><th>Cc myself:</th><td><input type="checkbox" name="cc_myself" /></td></tr>
>>> print f.as_ul()
<li>Subject: <input type="text" name="subject" maxlength="100" /></li>
<li>Message: <input type="text" name="message" /></li>
<li>Sender: <input type="text" name="sender" /></li>
<li>Cc myself: <input type="checkbox" name="cc_myself" /></li>
>>> print f.as_p()
<p>Subject: <input type="text" name="subject" maxlength="100" /></p>
<p>Message: <input type="text" name="message" /></p>
<p>Sender: <input type="text" name="sender" /></p>
<p>Cc myself: <input type="checkbox" name="cc_myself" /></p>
If ``auto_id`` is set to ``True``, then the form output *will* include
``<label>`` tags and will simply use the field name as its ``id`` for each form
field::
>>> f = ContactForm(auto_id=True)
>>> print f.as_table()
<tr><th><label for="subject">Subject:</label></th><td><input id="subject" type="text" name="subject" maxlength="100" /></td></tr>
<tr><th><label for="message">Message:</label></th><td><input type="text" name="message" id="message" /></td></tr>
<tr><th><label for="sender">Sender:</label></th><td><input type="text" name="sender" id="sender" /></td></tr>
<tr><th><label for="cc_myself">Cc myself:</label></th><td><input type="checkbox" name="cc_myself" id="cc_myself" /></td></tr>
>>> print f.as_ul()
<li><label for="subject">Subject:</label> <input id="subject" type="text" name="subject" maxlength="100" /></li>
<li><label for="message">Message:</label> <input type="text" name="message" id="message" /></li>
<li><label for="sender">Sender:</label> <input type="text" name="sender" id="sender" /></li>
<li><label for="cc_myself">Cc myself:</label> <input type="checkbox" name="cc_myself" id="cc_myself" /></li>
>>> print f.as_p()
<p><label for="subject">Subject:</label> <input id="subject" type="text" name="subject" maxlength="100" /></p>
<p><label for="message">Message:</label> <input type="text" name="message" id="message" /></p>
<p><label for="sender">Sender:</label> <input type="text" name="sender" id="sender" /></p>
<p><label for="cc_myself">Cc myself:</label> <input type="checkbox" name="cc_myself" id="cc_myself" /></p>
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_table()
<tr><th><label for="id_for_subject">Subject:</label></th><td><input id="id_for_subject" type="text" name="subject" maxlength="100" /></td></tr>
<tr><th><label for="id_for_message">Message:</label></th><td><input type="text" name="message" id="id_for_message" /></td></tr>
<tr><th><label for="id_for_sender">Sender:</label></th><td><input type="text" name="sender" id="id_for_sender" /></td></tr>
<tr><th><label for="id_for_cc_myself">Cc myself:</label></th><td><input type="checkbox" name="cc_myself" id="id_for_cc_myself" /></td></tr>
>>> print f.as_ul()
<li><label for="id_for_subject">Subject:</label> <input id="id_for_subject" type="text" name="subject" maxlength="100" /></li>
<li><label for="id_for_message">Message:</label> <input type="text" name="message" id="id_for_message" /></li>
<li><label for="id_for_sender">Sender:</label> <input type="text" name="sender" id="id_for_sender" /></li>
<li><label for="id_for_cc_myself">Cc myself:</label> <input type="checkbox" name="cc_myself" id="id_for_cc_myself" /></li>
>>> print f.as_p()
<p><label for="id_for_subject">Subject:</label> <input id="id_for_subject" type="text" name="subject" maxlength="100" /></p>
<p><label for="id_for_message">Message:</label> <input type="text" name="message" id="id_for_message" /></p>
<p><label for="id_for_sender">Sender:</label> <input type="text" name="sender" id="id_for_sender" /></p>
<p><label for="id_for_cc_myself">Cc myself:</label> <input type="checkbox" name="cc_myself" id="id_for_cc_myself" /></p>
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'``.
Normally, a colon (``:``) will be appended after any label name when a form is
rendered. It's possible to change the colon to another character, or omit it
entirely, using the ``label_suffix`` parameter::
>>> f = ContactForm(auto_id='id_for_%s', label_suffix='')
>>> print f.as_ul()
<li><label for="id_for_subject">Subject</label> <input id="id_for_subject" type="text" name="subject" maxlength="100" /></li>
<li><label for="id_for_message">Message</label> <input type="text" name="message" id="id_for_message" /></li>
<li><label for="id_for_sender">Sender</label> <input type="text" name="sender" id="id_for_sender" /></li>
<li><label for="id_for_cc_myself">Cc myself</label> <input type="checkbox" name="cc_myself" id="id_for_cc_myself" /></li>
>>> f = ContactForm(auto_id='id_for_%s', label_suffix=' ->')
>>> print f.as_ul()
<li><label for="id_for_subject">Subject -></label> <input id="id_for_subject" type="text" name="subject" maxlength="100" /></li>
<li><label for="id_for_message">Message -></label> <input type="text" name="message" id="id_for_message" /></li>
<li><label for="id_for_sender">Sender -></label> <input type="text" name="sender" id="id_for_sender" /></li>
<li><label for="id_for_cc_myself">Cc myself -></label> <input type="checkbox" name="cc_myself" id="id_for_cc_myself" /></li>
Note that the label suffix is added only if the last character of the
label isn't a punctuation character (``.``, ``!``, ``?`` or ``:``)
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, just change the order in which those fields are listed in the class.
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 e-mail 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" /></td></tr>
<tr><th>Message:</th><td><input type="text" name="message" value="Hi there" /></td></tr>
<tr><th>Sender:</th><td><ul class="errorlist"><li>Enter a valid e-mail address.</li></ul><input type="text" name="sender" value="invalid e-mail address" /></td></tr>
<tr><th>Cc myself:</th><td><input checked="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" /></li>
<li>Message: <input type="text" name="message" value="Hi there" /></li>
<li><ul class="errorlist"><li>Enter a valid e-mail address.</li></ul>Sender: <input type="text" name="sender" value="invalid e-mail address" /></li>
<li>Cc myself: <input checked="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" /></p>
<p>Message: <input type="text" name="message" value="Hi there" /></p>
<p><ul class="errorlist"><li>Enter a valid e-mail address.</li></ul></p>
<p>Sender: <input type="text" name="sender" value="invalid e-mail address" /></p>
<p>Cc myself: <input checked="checked" type="checkbox" name="cc_myself" /></p>
Customizing the error list format
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
By default, forms use ``django.forms.util.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.util import ErrorList
>>> class DivErrorList(ErrorList):
... def __unicode__(self):
... return self.as_divs()
... def as_divs(self):
... if not self: return u''
... return u'<div class="errorlist">%s</div>' % ''.join([u'<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" /></p>
<p>Message: <input type="text" name="message" value="Hi there" /></p>
<div class="errorlist"><div class="error">Enter a valid e-mail address.</div></div>
<p>Sender: <input type="text" name="sender" value="invalid e-mail address" /></p>
<p>Cc myself: <input checked="checked" type="checkbox" name="cc_myself" /></p>
More granular output
~~~~~~~~~~~~~~~~~~~~
The ``as_p()``, ``as_ul()`` and ``as_table()`` methods are simply shortcuts for
lazy developers -- they're not the only way a form object can be displayed.
To display the HTML for a single field in your form, use dictionary lookup
syntax using the field's name as the key, and print the resulting object::
>>> f = ContactForm()
>>> print f['subject']
<input id="id_subject" type="text" name="subject" maxlength="100" />
>>> print f['message']
<input type="text" name="message" id="id_message" />
>>> print f['sender']
<input type="text" name="sender" id="id_sender" />
>>> print f['cc_myself']
<input type="checkbox" name="cc_myself" id="id_cc_myself" />
Call ``str()`` or ``unicode()`` on the field to get its rendered HTML as a
string or Unicode object, respectively::
>>> str(f['subject'])
'<input id="id_subject" type="text" name="subject" maxlength="100" />'
>>> unicode(f['subject'])
u'<input id="id_subject" type="text" name="subject" maxlength="100" />'
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" />
>>> f = ContactForm(auto_id='id_%s')
>>> print f['message']
<input type="text" name="message" id="id_message" />
For a field's list of errors, access the field's ``errors`` attribute. This
is 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" />
>>> f['message'].errors
[u'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)
''
.. _binding-uploaded-files:
Binding uploaded files to a form
--------------------------------
**New in Django development version**
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 a image field
>>> f = ContactFormWithMugshot()
Testing for multipart forms
~~~~~~~~~~~~~~~~~~~~~~~~~~~
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_ul()
<li>Subject: <input type="text" name="subject" maxlength="100" /></li>
<li>Message: <input type="text" name="message" /></li>
<li>Sender: <input type="text" name="sender" /></li>
<li>Cc myself: <input type="checkbox" name="cc_myself" /></li>
<li>Priority: <input type="text" name="priority" /></li>
It's possible to subclass multiple forms, treating forms as "mix-ins." In this
example, ``BeatleForm`` subclasses both ``PersonForm`` and ``InstrumentForm``
(in that order), and its field list includes the fields from the parent
classes::
>>> class PersonForm(Form):
... first_name = CharField()
... last_name = CharField()
>>> class InstrumentForm(Form):
... instrument = CharField()
>>> class BeatleForm(PersonForm, InstrumentForm):
... haircut_type = CharField()
>>> b = BeatleForm(auto_id=False)
>>> print b.as_ul()
<li>First name: <input type="text" name="first_name" /></li>
<li>Last name: <input type="text" name="last_name" /></li>
<li>Instrument: <input type="text" name="instrument" /></li>
<li>Haircut type: <input type="text" name="haircut_type" /></li>
.. _form-prefix:
Prefixes for forms
------------------
.. attribute:: 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_ul()
<li><label for="id_mother-first_name">First name:</label> <input type="text" name="mother-first_name" id="id_mother-first_name" /></li>
<li><label for="id_mother-last_name">Last name:</label> <input type="text" name="mother-last_name" id="id_mother-last_name" /></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" /></li>
<li><label for="id_father-last_name">Last name:</label> <input type="text" name="father-last_name" id="id_father-last_name" /></li>