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django/docs/ref/forms/widgets.txt
Claude Paroz 909015a51b Fixed #22786 -- Documented value_from_datadict caveat 
Thanks blueyed for the report and Tim Graham for the review.
2014-08-29 10:24:50 +02:00

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=======
Widgets
=======
.. module:: django.forms.widgets
:synopsis: Django's built-in form widgets.
.. currentmodule:: django.forms
A widget is Django's representation of a HTML input element. The widget
handles the rendering of the HTML, and the extraction of data from a GET/POST
dictionary that corresponds to the widget.
.. tip::
Widgets should not be confused with the :doc:`form fields </ref/forms/fields>`.
Form fields deal with the logic of input validation and are used directly
in templates. Widgets deal with rendering of HTML form input elements on
the web page and extraction of raw submitted data. However, widgets do
need to be :ref:`assigned <widget-to-field>` to form fields.
.. _widget-to-field:
Specifying widgets
------------------
Whenever you specify a field on a form, Django will use a default widget
that is appropriate to the type of data that is to be displayed. To find
which widget is used on which field, see the documentation about
:ref:`built-in-fields`.
However, if you want to use a different widget for a field, you can
just use the :attr:`~Field.widget` argument on the field definition. For
example::
from django import forms
class CommentForm(forms.Form):
name = forms.CharField()
url = forms.URLField()
comment = forms.CharField(widget=forms.Textarea)
This would specify a form with a comment that uses a larger :class:`Textarea`
widget, rather than the default :class:`TextInput` widget.
Setting arguments for widgets
-----------------------------
Many widgets have optional extra arguments; they can be set when defining the
widget on the field. In the following example, the
:attr:`~django.forms.extras.widgets.SelectDateWidget.years` attribute is set
for a :class:`~django.forms.extras.widgets.SelectDateWidget`::
from django import forms
from django.forms.extras.widgets import SelectDateWidget
BIRTH_YEAR_CHOICES = ('1980', '1981', '1982')
FAVORITE_COLORS_CHOICES = (('blue', 'Blue'),
('green', 'Green'),
('black', 'Black'))
class SimpleForm(forms.Form):
birth_year = forms.DateField(widget=SelectDateWidget(years=BIRTH_YEAR_CHOICES))
favorite_colors = forms.MultipleChoiceField(required=False,
widget=forms.CheckboxSelectMultiple, choices=FAVORITE_COLORS_CHOICES)
See the :ref:`built-in widgets` for more information about which widgets
are available and which arguments they accept.
Widgets inheriting from the Select widget
-----------------------------------------
Widgets inheriting from the :class:`Select` widget deal with choices. They
present the user with a list of options to choose from. The different widgets
present this choice differently; the :class:`Select` widget itself uses a
``<select>`` HTML list representation, while :class:`RadioSelect` uses radio
buttons.
:class:`Select` widgets are used by default on :class:`ChoiceField` fields. The
choices displayed on the widget are inherited from the :class:`ChoiceField` and
changing :attr:`ChoiceField.choices` will update :attr:`Select.choices`. For
example::
>>> from django import forms
>>> CHOICES = (('1', 'First',), ('2', 'Second',))
>>> choice_field = forms.ChoiceField(widget=forms.RadioSelect, choices=CHOICES)
>>> choice_field.choices
[('1', 'First'), ('2', 'Second')]
>>> choice_field.widget.choices
[('1', 'First'), ('2', 'Second')]
>>> choice_field.widget.choices = ()
>>> choice_field.choices = (('1', 'First and only',),)
>>> choice_field.widget.choices
[('1', 'First and only')]
Widgets which offer a :attr:`~Select.choices` attribute can however be used
with fields which are not based on choice -- such as a :class:`CharField` --
but it is recommended to use a :class:`ChoiceField`-based field when the
choices are inherent to the model and not just the representational widget.
Customizing widget instances
----------------------------
When Django renders a widget as HTML, it only renders very minimal markup -
Django doesn't add class names, or any other widget-specific attributes. This
means, for example, that all :class:`TextInput` widgets will appear the same
on your Web pages.
There are two ways to customize widgets: :ref:`per widget instance
<styling-widget-instances>` and :ref:`per widget class <styling-widget-classes>`.
.. _styling-widget-instances:
Styling widget instances
^^^^^^^^^^^^^^^^^^^^^^^^
If you want to make one widget instance look different from another, you will
need to specify additional attributes at the time when the widget object is
instantiated and assigned to a form field (and perhaps add some rules to your
CSS files).
For example, take the following simple form::
from django import forms
class CommentForm(forms.Form):
name = forms.CharField()
url = forms.URLField()
comment = forms.CharField()
This form will include three default :class:`TextInput` widgets, with default
rendering -- no CSS class, no extra attributes. This means that the input boxes
provided for each widget will be rendered exactly the same::
>>> f = CommentForm(auto_id=False)
>>> f.as_table()
<tr><th>Name:</th><td><input type="text" name="name" /></td></tr>
<tr><th>Url:</th><td><input type="url" name="url"/></td></tr>
<tr><th>Comment:</th><td><input type="text" name="comment" /></td></tr>
On a real Web page, you probably don't want every widget to look the same. You
might want a larger input element for the comment, and you might want the
'name' widget to have some special CSS class. It is also possible to specify
the 'type' attribute to take advantage of the new HTML5 input types. To do
this, you use the :attr:`Widget.attrs` argument when creating the widget::
class CommentForm(forms.Form):
name = forms.CharField(widget=forms.TextInput(attrs={'class': 'special'}))
url = forms.URLField()
comment = forms.CharField(widget=forms.TextInput(attrs={'size': '40'}))
Django will then include the extra attributes in the rendered output:
>>> f = CommentForm(auto_id=False)
>>> f.as_table()
<tr><th>Name:</th><td><input type="text" name="name" class="special"/></td></tr>
<tr><th>Url:</th><td><input type="url" name="url"/></td></tr>
<tr><th>Comment:</th><td><input type="text" name="comment" size="40"/></td></tr>
You can also set the HTML ``id`` using :attr:`~Widget.attrs`. See
:attr:`BoundField.id_for_label` for an example.
.. _styling-widget-classes:
Styling widget classes
^^^^^^^^^^^^^^^^^^^^^^
With widgets, it is possible to add assets (``css`` and ``javascript``)
and more deeply customize their appearance and behavior.
In a nutshell, you will need to subclass the widget and either
:ref:`define a "Media" inner class <assets-as-a-static-definition>` or
:ref:`create a "media" property <dynamic-property>`.
These methods involve somewhat advanced Python programming and are described in
detail in the :doc:`Form Assets </topics/forms/media>` topic guide.
.. _base-widget-classes:
Base Widget classes
-------------------
Base widget classes :class:`Widget` and :class:`MultiWidget` are subclassed by
all the :ref:`built-in widgets <built-in widgets>` and may serve as a
foundation for custom widgets.
.. class:: Widget(attrs=None)
This abstract class cannot be rendered, but provides the basic attribute
:attr:`~Widget.attrs`. You may also implement or override the
:meth:`~Widget.render()` method on custom widgets.
.. attribute:: Widget.attrs
A dictionary containing HTML attributes to be set on the rendered
widget.
.. code-block:: pycon
>>> from django import forms
>>> name = forms.TextInput(attrs={'size': 10, 'title': 'Your name',})
>>> name.render('name', 'A name')
'<input title="Your name" type="text" name="name" value="A name" size="10" />'
.. versionchanged:: 1.8
If you assign a value of ``True`` or ``False`` to an attribute,
it will be rendered as an HTML5 boolean attribute::
>>> name = forms.TextInput(attrs={'required': True})
>>> name.render('name', 'A name')
'<input name="name" type="text" value="A name" required />'
>>>
>>> name = forms.TextInput(attrs={'required': False})
>>> name.render('name', 'A name')
'<input name="name" type="text" value="A name" />'
.. method:: render(name, value, attrs=None)
Returns HTML for the widget, as a Unicode string. This method must be
implemented by the subclass, otherwise ``NotImplementedError`` will be
raised.
The 'value' given is not guaranteed to be valid input, therefore
subclass implementations should program defensively.
.. method:: value_from_datadict(data, files, name)
Given a dictionary of data and this widget's name, returns the value
of this widget. ``files`` may contain data coming from
:attr:`request.FILES <django.http.HttpRequest.FILES>`. Returns ``None``
if a value wasn't provided. Note also that ``value_from_datadict`` may
be called more than once during handling of form data, so if you
customize it and add expensive processing, you should implement some
caching mechanism yourself.
.. class:: MultiWidget(widgets, attrs=None)
A widget that is composed of multiple widgets.
:class:`~django.forms.MultiWidget` works hand in hand with the
:class:`~django.forms.MultiValueField`.
:class:`MultiWidget` has one required argument:
.. attribute:: MultiWidget.widgets
An iterable containing the widgets needed.
And one required method:
.. method:: decompress(value)
This method takes a single "compressed" value from the field and
returns a list of "decompressed" values. The input value can be
assumed valid, but not necessarily non-empty.
This method **must be implemented** by the subclass, and since the
value may be empty, the implementation must be defensive.
The rationale behind "decompression" is that it is necessary to "split"
the combined value of the form field into the values for each widget.
An example of this is how :class:`SplitDateTimeWidget` turns a
:class:`~datetime.datetime` value into a list with date and time split
into two separate values::
from django.forms import MultiWidget
class SplitDateTimeWidget(MultiWidget):
# ...
def decompress(self, value):
if value:
return [value.date(), value.time().replace(microsecond=0)]
return [None, None]
.. tip::
Note that :class:`~django.forms.MultiValueField` has a
complementary method :meth:`~django.forms.MultiValueField.compress`
with the opposite responsibility - to combine cleaned values of
all member fields into one.
Other methods that may be useful to override include:
.. method:: render(name, value, attrs=None)
Argument ``value`` is handled differently in this method from the
subclasses of :class:`~Widget` because it has to figure out how to
split a single value for display in multiple widgets.
The ``value`` argument used when rendering can be one of two things:
* A ``list``.
* A single value (e.g., a string) that is the "compressed" representation
of a ``list`` of values.
If ``value`` is a list, the output of :meth:`~MultiWidget.render` will
be a concatenation of rendered child widgets. If ``value`` is not a
list, it will first be processed by the method
:meth:`~MultiWidget.decompress()` to create the list and then rendered.
When ``render()`` executes its HTML rendering, each value in the list
is rendered with the corresponding widget -- the first value is
rendered in the first widget, the second value is rendered in the
second widget, etc.
Unlike in the single value widgets, method :meth:`~MultiWidget.render`
need not be implemented in the subclasses.
.. method:: format_output(rendered_widgets)
Given a list of rendered widgets (as strings), returns a Unicode string
representing the HTML for the whole lot.
This hook allows you to format the HTML design of the widgets any way
you'd like.
Here's an example widget which subclasses :class:`MultiWidget` to display
a date with the day, month, and year in different select boxes. This widget
is intended to be used with a :class:`~django.forms.DateField` rather than
a :class:`~django.forms.MultiValueField`, thus we have implemented
:meth:`~Widget.value_from_datadict`::
from datetime import date
from django.forms import widgets
class DateSelectorWidget(widgets.MultiWidget):
def __init__(self, attrs=None):
# create choices for days, months, years
# example below, the rest snipped for brevity.
years = [(year, year) for year in (2011, 2012, 2013)]
_widgets = (
widgets.Select(attrs=attrs, choices=days),
widgets.Select(attrs=attrs, choices=months),
widgets.Select(attrs=attrs, choices=years),
)
super(DateSelectorWidget, self).__init__(_widgets, attrs)
def decompress(self, value):
if value:
return [value.day, value.month, value.year]
return [None, None, None]
def format_output(self, rendered_widgets):
return ''.join(rendered_widgets)
def value_from_datadict(self, data, files, name):
datelist = [
widget.value_from_datadict(data, files, name + '_%s' % i)
for i, widget in enumerate(self.widgets)]
try:
D = date(day=int(datelist[0]), month=int(datelist[1]),
year=int(datelist[2]))
except ValueError:
return ''
else:
return str(D)
The constructor creates several :class:`Select` widgets in a tuple. The
``super`` class uses this tuple to setup the widget.
The :meth:`~MultiWidget.format_output` method is fairly vanilla here (in
fact, it's the same as what's been implemented as the default for
``MultiWidget``), but the idea is that you could add custom HTML between
the widgets should you wish.
The required method :meth:`~MultiWidget.decompress` breaks up a
``datetime.date`` value into the day, month, and year values corresponding
to each widget. Note how the method handles the case where ``value`` is
``None``.
The default implementation of :meth:`~Widget.value_from_datadict` returns
a list of values corresponding to each ``Widget``. This is appropriate
when using a ``MultiWidget`` with a :class:`~django.forms.MultiValueField`,
but since we want to use this widget with a :class:`~django.forms.DateField`
which takes a single value, we have overridden this method to combine the
data of all the subwidgets into a ``datetime.date``. The method extracts
data from the ``POST`` dictionary and constructs and validates the date.
If it is valid, we return the string, otherwise, we return an empty string
which will cause ``form.is_valid`` to return ``False``.
.. _built-in widgets:
Built-in widgets
----------------
Django provides a representation of all the basic HTML widgets, plus some
commonly used groups of widgets in the ``django.forms.widgets`` module,
including :ref:`the input of text <text-widgets>`, :ref:`various checkboxes
and selectors <selector-widgets>`, :ref:`uploading files <file-upload-widgets>`,
and :ref:`handling of multi-valued input <composite-widgets>`.
.. _text-widgets:
Widgets handling input of text
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
These widgets make use of the HTML elements ``input`` and ``textarea``.
``TextInput``
~~~~~~~~~~~~~
.. class:: TextInput
Text input: ``<input type="text" ...>``
``NumberInput``
~~~~~~~~~~~~~~~
.. class:: NumberInput
Text input: ``<input type="number" ...>``
Beware that not all browsers support entering localized numbers in
``number`` input types. Django itself avoids using them for fields having
their :attr:`~django.forms.Field.localize` property to ``True``.
``EmailInput``
~~~~~~~~~~~~~~
.. class:: EmailInput
Text input: ``<input type="email" ...>``
``URLInput``
~~~~~~~~~~~~
.. class:: URLInput
Text input: ``<input type="url" ...>``
``PasswordInput``
~~~~~~~~~~~~~~~~~
.. class:: PasswordInput
Password input: ``<input type='password' ...>``
Takes one optional argument:
.. attribute:: PasswordInput.render_value
Determines whether the widget will have a value filled in when the
form is re-displayed after a validation error (default is ``False``).
``HiddenInput``
~~~~~~~~~~~~~~~
.. class:: HiddenInput
Hidden input: ``<input type='hidden' ...>``
Note that there also is a :class:`MultipleHiddenInput` widget that
encapsulates a set of hidden input elements.
``DateInput``
~~~~~~~~~~~~~
.. class:: DateInput
Date input as a simple text box: ``<input type='text' ...>``
Takes same arguments as :class:`TextInput`, with one more optional argument:
.. attribute:: DateInput.format
The format in which this field's initial value will be displayed.
If no ``format`` argument is provided, the default format is the first
format found in :setting:`DATE_INPUT_FORMATS` and respects
:ref:`format-localization`.
``DateTimeInput``
~~~~~~~~~~~~~~~~~
.. class:: DateTimeInput
Date/time input as a simple text box: ``<input type='text' ...>``
Takes same arguments as :class:`TextInput`, with one more optional argument:
.. attribute:: DateTimeInput.format
The format in which this field's initial value will be displayed.
If no ``format`` argument is provided, the default format is the first
format found in :setting:`DATETIME_INPUT_FORMATS` and respects
:ref:`format-localization`.
``TimeInput``
~~~~~~~~~~~~~
.. class:: TimeInput
Time input as a simple text box: ``<input type='text' ...>``
Takes same arguments as :class:`TextInput`, with one more optional argument:
.. attribute:: TimeInput.format
The format in which this field's initial value will be displayed.
If no ``format`` argument is provided, the default format is the first
format found in :setting:`TIME_INPUT_FORMATS` and respects
:ref:`format-localization`.
``Textarea``
~~~~~~~~~~~~
.. class:: Textarea
Text area: ``<textarea>...</textarea>``
.. _selector-widgets:
Selector and checkbox widgets
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
``CheckboxInput``
~~~~~~~~~~~~~~~~~
.. class:: CheckboxInput
Checkbox: ``<input type='checkbox' ...>``
Takes one optional argument:
.. attribute:: CheckboxInput.check_test
A callable that takes the value of the ``CheckboxInput`` and returns
``True`` if the checkbox should be checked for that value.
``Select``
~~~~~~~~~~
.. class:: Select
Select widget: ``<select><option ...>...</select>``
.. attribute:: Select.choices
This attribute is optional when the form field does not have a
``choices`` attribute. If it does, it will override anything you set
here when the attribute is updated on the :class:`Field`.
``NullBooleanSelect``
~~~~~~~~~~~~~~~~~~~~~
.. class:: NullBooleanSelect
Select widget with options 'Unknown', 'Yes' and 'No'
``SelectMultiple``
~~~~~~~~~~~~~~~~~~
.. class:: SelectMultiple
Similar to :class:`Select`, but allows multiple selection:
``<select multiple='multiple'>...</select>``
``RadioSelect``
~~~~~~~~~~~~~~~
.. class:: RadioSelect
Similar to :class:`Select`, but rendered as a list of radio buttons within
``<li>`` tags:
.. code-block:: html
<ul>
<li><input type='radio' name='...'></li>
...
</ul>
For more granular control over the generated markup, you can loop over the
radio buttons in the template. Assuming a form ``myform`` with a field
``beatles`` that uses a ``RadioSelect`` as its widget:
.. code-block:: html+django
{% for radio in myform.beatles %}
<div class="myradio">
{{ radio }}
</div>
{% endfor %}
This would generate the following HTML:
.. code-block:: html
<div class="myradio">
<label for="id_beatles_0"><input id="id_beatles_0" name="beatles" type="radio" value="john" /> John</label>
</div>
<div class="myradio">
<label for="id_beatles_1"><input id="id_beatles_1" name="beatles" type="radio" value="paul" /> Paul</label>
</div>
<div class="myradio">
<label for="id_beatles_2"><input id="id_beatles_2" name="beatles" type="radio" value="george" /> George</label>
</div>
<div class="myradio">
<label for="id_beatles_3"><input id="id_beatles_3" name="beatles" type="radio" value="ringo" /> Ringo</label>
</div>
That included the ``<label>`` tags. To get more granular, you can use each
radio button's ``tag``, ``choice_label`` and ``id_for_label`` attributes.
For example, this template...
.. code-block:: html+django
{% for radio in myform.beatles %}
<label for="{{ radio.id_for_label }}">
{{ radio.choice_label }}
<span class="radio">{{ radio.tag }}</span>
</label>
{% endfor %}
...will result in the following HTML:
.. code-block:: html
<label for="id_beatles_0">
John
<span class="radio"><input id="id_beatles_0" name="beatles" type="radio" value="john" /></span>
</label>
<label for="id_beatles_1">
Paul
<span class="radio"><input id="id_beatles_1" name="beatles" type="radio" value="paul" /></span>
</label>
<label for="id_beatles_2">
George
<span class="radio"><input id="id_beatles_2" name="beatles" type="radio" value="george" /></span>
</label>
<label for="id_beatles_3">
Ringo
<span class="radio"><input id="id_beatles_3" name="beatles" type="radio" value="ringo" /></span>
</label>
If you decide not to loop over the radio buttons -- e.g., if your template
simply includes ``{{ myform.beatles }}`` -- they'll be output in a ``<ul>``
with ``<li>`` tags, as above.
The outer ``<ul>`` container will receive the ``id`` attribute defined on
the widget.
.. versionchanged:: 1.7
When looping over the radio buttons, the ``label`` and ``input`` tags include
``for`` and ``id`` attributes, respectively. Each radio button has an
``id_for_label`` attribute to output the element's ID.
``CheckboxSelectMultiple``
~~~~~~~~~~~~~~~~~~~~~~~~~~
.. class:: CheckboxSelectMultiple
Similar to :class:`SelectMultiple`, but rendered as a list of check
buttons:
.. code-block:: html
<ul>
<li><input type='checkbox' name='...' ></li>
...
</ul>
The outer ``<ul>`` container will receive the ``id`` attribute defined on
the widget.
Like :class:`RadioSelect`, you can now loop over the individual checkboxes making
up the lists. See the documentation of :class:`RadioSelect` for more details.
.. versionchanged:: 1.7
When looping over the checkboxes, the ``label`` and ``input`` tags include
``for`` and ``id`` attributes, respectively. Each checkbox has an
``id_for_label`` attribute to output the element's ID.
.. _file-upload-widgets:
File upload widgets
^^^^^^^^^^^^^^^^^^^
``FileInput``
~~~~~~~~~~~~~
.. class:: FileInput
File upload input: ``<input type='file' ...>``
``ClearableFileInput``
~~~~~~~~~~~~~~~~~~~~~~
.. class:: ClearableFileInput
File upload input: ``<input type='file' ...>``, with an additional checkbox
input to clear the field's value, if the field is not required and has
initial data.
.. _composite-widgets:
Composite widgets
^^^^^^^^^^^^^^^^^
``MultipleHiddenInput``
~~~~~~~~~~~~~~~~~~~~~~~
.. class:: MultipleHiddenInput
Multiple ``<input type='hidden' ...>`` widgets.
A widget that handles multiple hidden widgets for fields that have a list
of values.
.. attribute:: MultipleHiddenInput.choices
This attribute is optional when the form field does not have a
``choices`` attribute. If it does, it will override anything you set
here when the attribute is updated on the :class:`Field`.
``SplitDateTimeWidget``
~~~~~~~~~~~~~~~~~~~~~~~
.. class:: SplitDateTimeWidget
Wrapper (using :class:`MultiWidget`) around two widgets: :class:`DateInput`
for the date, and :class:`TimeInput` for the time.
``SplitDateTimeWidget`` has two optional attributes:
.. attribute:: SplitDateTimeWidget.date_format
Similar to :attr:`DateInput.format`
.. attribute:: SplitDateTimeWidget.time_format
Similar to :attr:`TimeInput.format`
``SplitHiddenDateTimeWidget``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.. class:: SplitHiddenDateTimeWidget
Similar to :class:`SplitDateTimeWidget`, but uses :class:`HiddenInput` for
both date and time.
.. currentmodule:: django.forms.extras.widgets
``SelectDateWidget``
~~~~~~~~~~~~~~~~~~~~
.. class:: SelectDateWidget
Wrapper around three :class:`~django.forms.Select` widgets: one each for
month, day, and year. Note that this widget lives in a separate file from
the standard widgets.
Takes one optional argument:
.. attribute:: SelectDateWidget.years
An optional list/tuple of years to use in the "year" select box.
The default is a list containing the current year and the next 9 years.
.. attribute:: SelectDateWidget.months
.. versionadded:: 1.7
An optional dict of months to use in the "months" select box.
The keys of the dict correspond to the month number (1-indexed) and
the values are the displayed months::
MONTHS = {
1:_('jan'), 2:_('feb'), 3:_('mar'), 4:_('apr'),
5:_('may'), 6:_('jun'), 7:_('jul'), 8:_('aug'),
9:_('sep'), 10:_('oct'), 11:_('nov'), 12:_('dec')
}
.. attribute:: SelectDateWidget.empty_label
.. versionadded:: 1.8
If the :class:`~django.forms.DateField` is not required,
:class:`SelectDateWidget` will have an empty choice at the top of the
list (which is ``---`` by default). You can change the text of this
label with the ``empty_label`` attribute. ``empty_label`` can be a
``string``, ``list``, or ``tuple``. When a string is used, all select
boxes will each have an empty choice with this label. If ``empty_label``
is a ``list`` or ``tuple`` of 3 string elements, the select boxes will
have their own custom label. The labels should be in this order
``('year_label', 'month_label', 'day_label')``.
.. code-block:: python
# A custom empty label with string
field1 = forms.DateField(widget=SelectDateWidget(empty_label="Nothing"))
# A custom empty label with tuple
field1 = forms.DateField(widget=SelectDateWidget(
empty_label=("Choose Year", "Choose Month", "Choose Day"))
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