Django2.0手册:Widgets



A widget is Django’s representation of an 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.

The HTML generated by the built-in widgets uses HTML5 syntax, targeting
<!DOCTYPE html>. For example, it uses boolean attributes such as checked
rather than the XHTML style of checked='checked'.

Tip

Widgets should not be confused with the form 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 assigned to form fields.

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
Built-in Field classes.

However, if you want to use a different widget for a field, you can
just use the 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 Textarea
widget, rather than the default 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
years attribute is set for a
SelectDateWidget:

from django import forms

BIRTH_YEAR_CHOICES = ('1980', '1981', '1982')
FAVORITE_COLORS_CHOICES = (
    ('blue', 'Blue'),
    ('green', 'Green'),
    ('black', 'Black'),
)

class SimpleForm(forms.Form):
    birth_year = forms.DateField(widget=forms.SelectDateWidget(years=BIRTH_YEAR_CHOICES))
    favorite_colors = forms.MultipleChoiceField(
        required=False,
        widget=forms.CheckboxSelectMultiple,
        choices=FAVORITE_COLORS_CHOICES,
    )

See the 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 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 Select widget itself uses a
<select> HTML list representation, while RadioSelect uses radio
buttons.

Select widgets are used by default on ChoiceField fields. The
choices displayed on the widget are inherited from the ChoiceField and
changing ChoiceField.choices will update 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 choices attribute can however be used
with fields which are not based on choice — such as a CharField
but it is recommended to use a 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 TextInput widgets will appear the same
on your Web pages.

There are two ways to customize widgets: per widget instance and per widget class.

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 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" 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>

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 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'}))

You can also modify a widget in the form definition:

class CommentForm(forms.Form):
    name = forms.CharField()
    url = forms.URLField()
    comment = forms.CharField()

    name.widget.attrs.update({'class': 'special'})
    comment.widget.attrs.update(size='40')

Or if the field isn’t declared directly on the form (such as model form fields),
you can use the Form.fields attribute:

class CommentForm(forms.ModelForm):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.fields['name'].widget.attrs.update({'class': 'special'})
        self.fields['comment'].widget.attrs.update(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" 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" size="40" required /></td></tr>

You can also set the HTML id using attrs. See
BoundField.id_for_label for an example.

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
define a “Media” inner class or
create a “media” property.

These methods involve somewhat advanced Python programming and are described in
detail in the Form Assets topic guide.

Base widget classes¶

Base widget classes Widget and MultiWidget are subclassed by
all the built-in widgets and may serve as a
foundation for custom widgets.

Widget¶

class Widget(attrs=None)[source]

This abstract class cannot be rendered, but provides the basic attribute
attrs. You may also implement or override the
render() method on custom widgets.

attrs

A dictionary containing HTML attributes to be set on the rendered
widget.

>>> 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" />'

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" />'
supports_microseconds

An attribute that defaults to True. If set to False, the
microseconds part of datetime and
time values will be set to 0.

format_value(value)[source]

Cleans and returns a value for use in the widget template. value
isn’t guaranteed to be valid input, therefore subclass implementations
should program defensively.

get_context(name, value, attrs)[source]
New in Django 1.11.

Returns a dictionary of values to use when rendering the widget
template. By default, the dictionary contains a single key,
'widget', which is a dictionary representation of the widget
containing the following keys:

  • 'name': The name of the field from the name argument.
  • 'is_hidden': A boolean indicating whether or not this widget is
    hidden.
  • 'required': A boolean indicating whether or not the field for
    this widget is required.
  • 'value': The value as returned by format_value().
  • 'attrs': HTML attributes to be set on the rendered widget. The
    combination of the attrs attribute and the attrs argument.
  • 'template_name': The value of self.template_name.

Widget subclasses can provide custom context values by overriding
this method.

id_for_label(id_)[source]

Returns the HTML ID attribute of this widget for use by a <label>,
given the ID of the field. Returns None if an ID isn’t available.

This hook is necessary because some widgets have multiple HTML
elements and, thus, multiple IDs. In that case, this method should
return an ID value that corresponds to the first ID in the widget’s
tags.

render(name, value, attrs=None, renderer=None)[source]

Renders a widget to HTML using the given renderer. If renderer is
None, the renderer from the FORM_RENDERER setting is
used.

Changed in Django 1.11:

The renderer argument was added. Support for subclasses that
don’t accept it will be removed in Django 2.1.

value_from_datadict(data, files, name)[source]

Given a dictionary of data and this widget’s name, returns the value
of this widget. files may contain data coming from
request.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.

value_omitted_from_data(data, files, name)[source]

Given data and files dictionaries and this widget’s name,
returns whether or not there’s data or files for the widget.

The method’s result affects whether or not a field in a model form
falls back to its default.

Special cases are CheckboxInput,
CheckboxSelectMultiple, and
SelectMultiple, which always return
False because an unchecked checkbox and unselected
<select multiple> don’t appear in the data of an HTML form
submission, so it’s unknown whether or not the user submitted a value.

use_required_attribute(initial)[source]

Given a form field’s initial value, returns whether or not the
widget can be rendered with the required HTML attribute. Forms use
this method along with Field.required and Form.use_required_attribute to determine whether or not
to display the required attribute for each field.

By default, returns False for hidden widgets and True
otherwise. Special cases are ClearableFileInput,
which returns False when initial is not set, and
CheckboxSelectMultiple, which always returns
False because browser validation would require all checkboxes to be
checked instead of at least one.

Override this method in custom widgets that aren’t compatible with
browser validation. For example, a WSYSIWG text editor widget backed by
a hidden textarea element may want to always return False to
avoid browser validation on the hidden field.

MultiWidget¶

class MultiWidget(widgets, attrs=None)[source]

A widget that is composed of multiple widgets.
MultiWidget works hand in hand with the
MultiValueField.

MultiWidget has one required argument:

widgets

An iterable containing the widgets needed.

And one required method:

decompress(value)[source]

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 SplitDateTimeWidget turns a
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 MultiValueField has a
complementary method compress()
with the opposite responsibility – to combine cleaned values of
all member fields into one.

It provides some custom context:

get_context(name, value, attrs)[source]

In addition to the 'widget' key described in
Widget.get_context(), MultiValueWidget adds a
widget['subwidgets'] key.

These can be looped over in the widget template:

{% for subwidget in widget.subwidgets %}
    {% include widget.template_name with widget=subwidget %}
{% endfor %}

Here’s an example widget which subclasses MultiWidget to display
a date with the day, month, and year in different select boxes. This widget
is intended to be used with a DateField rather than
a MultiValueField, thus we have implemented
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().__init__(_widgets, attrs)

    def decompress(self, value):
        if value:
            return [value.day, value.month, value.year]
        return [None, None, None]

    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 Select widgets in a tuple. The
super class uses this tuple to setup the widget.

The required method 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 value_from_datadict() returns
a list of values corresponding to each Widget. This is appropriate
when using a MultiWidget with a MultiValueField,
but since we want to use this widget with a 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¶

Django provides a representation of all the basic HTML widgets, plus some
commonly used groups of widgets in the django.forms.widgets module,
including the input of text, various checkboxes
and selectors
, uploading files,
and handling of multi-valued input.

Widgets handling input of text¶

These widgets make use of the HTML elements input and textarea.

TextInput

class TextInput[source]
  • input_type: 'text'
  • template_name: 'django/forms/widgets/text.html'
  • Renders as: <input type="text" ...>

NumberInput

class NumberInput[source]
  • input_type: 'number'
  • template_name: 'django/forms/widgets/number.html'
  • Renders as: <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 localize property set to True.

EmailInput

class EmailInput[source]
  • input_type: 'email'
  • template_name: 'django/forms/widgets/email.html'
  • Renders as: <input type="email" ...>

URLInput

class URLInput[source]
  • input_type: 'url'
  • template_name: 'django/forms/widgets/url.html'
  • Renders as: <input type="url" ...>

PasswordInput

class PasswordInput[source]
  • input_type: 'password'
  • template_name: 'django/forms/widgets/password.html'
  • Renders as: <input type="password" ...>

Takes one optional argument:

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[source]
  • input_type: 'hidden'
  • template_name: 'django/forms/widgets/hidden.html'
  • Renders as: <input type="hidden" ...>

Note that there also is a MultipleHiddenInput widget that
encapsulates a set of hidden input elements.

DateInput

class DateInput[source]
  • input_type: 'text'
  • template_name: 'django/forms/widgets/date.html'
  • Renders as: <input type="text" ...>

Takes same arguments as TextInput, with one more optional argument:

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 DATE_INPUT_FORMATS and respects
Format localization.

DateTimeInput

class DateTimeInput[source]
  • input_type: 'text'
  • template_name: 'django/forms/widgets/datetime.html'
  • Renders as: <input type="text" ...>

Takes same arguments as TextInput, with one more optional argument:

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 DATETIME_INPUT_FORMATS and respects
Format localization.

By default, the microseconds part of the time value is always set to 0.
If microseconds are required, use a subclass with the
supports_microseconds attribute set to True.

TimeInput

class TimeInput[source]
  • input_type: 'text'
  • template_name: 'django/forms/widgets/time.html'
  • Renders as: <input type="text" ...>

Takes same arguments as TextInput, with one more optional argument:

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 TIME_INPUT_FORMATS and respects
Format localization.

For the treatment of microseconds, see DateTimeInput.

Textarea

class Textarea[source]
  • template_name: 'django/forms/widgets/textarea.html'
  • Renders as: <textarea>...</textarea>

Selector and checkbox widgets¶

These widgets make use of the HTML elements <select>,
<input type="checkbox">, and <input type="radio">.

Widgets that render multiple choices have an option_template_name attribute
that specifies the template used to render each choice. For example, for the
Select widget, select_option.html renders the <option> for a
<select>.

CheckboxInput

class CheckboxInput[source]
  • input_type: 'checkbox'
  • template_name: 'django/forms/widgets/checkbox.html'
  • Renders as: <input type="checkbox" ...>

Takes one optional argument:

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[source]
  • template_name: 'django/forms/widgets/select.html'
  • option_template_name: 'django/forms/widgets/select_option.html'
  • Renders as: <select><option ...>...</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 Field.

NullBooleanSelect

class NullBooleanSelect[source]
  • template_name: 'django/forms/widgets/select.html'
  • option_template_name: 'django/forms/widgets/select_option.html'

Select widget with options ‘Unknown’, ‘Yes’ and ‘No’

SelectMultiple

class SelectMultiple[source]
  • template_name: 'django/forms/widgets/select.html'
  • option_template_name: 'django/forms/widgets/select_option.html'

Similar to Select, but allows multiple selection:
<select multiple="multiple">...</select>

RadioSelect

class RadioSelect[source]
  • template_name: 'django/forms/widgets/radio.html'
  • option_template_name: 'django/forms/widgets/radio_option.html'

Similar to Select, but rendered as a list of radio buttons within
<li> tags:

<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:

{% for radio in myform.beatles %}
<div class="myradio">
    {{ radio }}
</div>
{% endfor %}

This would generate the following HTML:

<div class="myradio">
    <label for="id_beatles_0"><input id="id_beatles_0" name="beatles" type="radio" value="john" required /> John</label>
</div>
<div class="myradio">
    <label for="id_beatles_1"><input id="id_beatles_1" name="beatles" type="radio" value="paul" required /> Paul</label>
</div>
<div class="myradio">
    <label for="id_beatles_2"><input id="id_beatles_2" name="beatles" type="radio" value="george" required /> George</label>
</div>
<div class="myradio">
    <label for="id_beatles_3"><input id="id_beatles_3" name="beatles" type="radio" value="ringo" required /> 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…

{% 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:

<label for="id_beatles_0">
    John
    <span class="radio"><input id="id_beatles_0" name="beatles" type="radio" value="john" required /></span>
</label>

<label for="id_beatles_1">
    Paul
    <span class="radio"><input id="id_beatles_1" name="beatles" type="radio" value="paul" required /></span>
</label>

<label for="id_beatles_2">
    George
    <span class="radio"><input id="id_beatles_2" name="beatles" type="radio" value="george" required /></span>
</label>

<label for="id_beatles_3">
    Ringo
    <span class="radio"><input id="id_beatles_3" name="beatles" type="radio" value="ringo" required /></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 receives the id attribute of the widget,
if defined, or BoundField.auto_id otherwise.

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[source]
  • template_name: 'django/forms/widgets/checkbox_select.html'
  • option_template_name: 'django/forms/widgets/checkbox_option.html'

Similar to SelectMultiple, but rendered as a list of checkboxes:

<ul>
  <li><input type="checkbox" name="..." ></li>
  ...
</ul>

The outer <ul> container receives the id attribute of the widget,
if defined, or BoundField.auto_id otherwise.

Like RadioSelect, you can loop over the individual checkboxes for the
widget’s choices. Unlike RadioSelect, the checkboxes won’t include the
required HTML attribute if the field is required because browser validation
would require all checkboxes to be checked instead of at least one.

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¶

FileInput

class FileInput[source]
  • template_name: 'django/forms/widgets/file.html'
  • Renders as: <input type="file" ...>

ClearableFileInput

class ClearableFileInput[source]
  • template_name: 'django/forms/widgets/clearable_file_input.html'
  • Renders as: <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¶

MultipleHiddenInput

class MultipleHiddenInput[source]
  • template_name: 'django/forms/widgets/multiple_hidden.html'
  • Renders as: multiple <input type="hidden" ...> tags

A widget that handles multiple hidden widgets for fields that have a list
of values.

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 Field.

SplitDateTimeWidget

class SplitDateTimeWidget[source]
  • template_name: 'django/forms/widgets/splitdatetime.html'

Wrapper (using MultiWidget) around two widgets: DateInput
for the date, and TimeInput for the time. Must be used with
SplitDateTimeField rather than DateTimeField.

SplitDateTimeWidget has several optional arguments:

date_format

Similar to DateInput.format

time_format

Similar to TimeInput.format

date_attrs
time_attrs
New in Django 2.0.

Similar to Widget.attrs. A dictionary containing HTML
attributes to be set on the rendered DateInput and
TimeInput widgets, respectively. If these attributes aren’t
set, Widget.attrs is used instead.

SplitHiddenDateTimeWidget

class SplitHiddenDateTimeWidget[source]
  • template_name: 'django/forms/widgets/splithiddendatetime.html'

Similar to SplitDateTimeWidget, but uses HiddenInput for
both date and time.

SelectDateWidget

class SelectDateWidget[source]
  • template_name: 'django/forms/widgets/select_date.html'

Wrapper around three Select widgets: one each for
month, day, and year.

Takes several optional arguments:

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.

months

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')
}
empty_label

If the DateField is not required,
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').

# 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"),
    ),
)