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 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.
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.
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.forms.fields import DateField, ChoiceField, MultipleChoiceField
from django.forms.widgets import RadioSelect, CheckboxSelectMultiple
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 = DateField(widget=SelectDateWidget(years=BIRTH_YEAR_CHOICES))
favorite_colors = forms.MultipleChoiceField(required=False,
widget=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 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.
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.
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" /></td></tr>
<tr><th>Url:</th><td><input type="text" 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 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="text" name="url"/></td></tr>
<tr><th>Comment:</th><td><input type="text" name="comment" size="40"/></td></tr>
With widgets, it is possible to add media (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 class “Media” as a member of the subclass, or create a property “media”, returning an instance of that class.
These methods involve somewhat advanced Python programming and are described in detail in the Form Media topic guide.
Base widget classes Widget and MultiWidget are subclassed by all the built-in widgets and may serve as a foundation for custom widgets.
This abstract class cannot be rendered, but provides the basic attribute attrs. You may also implement or override the render() method on custom widgets.
A dictionary containing HTML attributes to be set on the rendered widget.
>>> name = forms.TextInput(attrs={'size': 10, 'title': 'Your name',})
>>> name.render('name', 'A name')
u'<input title="Your name" type="text" name="name" value="A name" size="10" />'
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.
Given a dictionary of data and this widget’s name, returns the value of this widget. Returns None if a value wasn’t provided.
A widget that is composed of multiple widgets. MultiWidget works hand in hand with the MultiValueField.
MultiWidget has one required argument:
An iterable containing the widgets needed.
And one required method:
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:
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.
Other methods that may be useful to override include:
Argument value is handled differently in this method from the subclasses of 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:
If value is a list, output of render() will be a concatenation of rendered child widgets. If value is not a list, it will be first processed by the method decompress() to create the list and then processed as above.
In the second case – i.e., if the value is not a list – render() will first decompress the value into a list before rendering it. It does so by calling the decompress() method, which MultiWidget‘s subclasses must implement (see above).
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 render() need not be implemented in the subclasses.
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 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(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 u''.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 Select widgets in a tuple. The super class uses this tuple to setup the widget.
The 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 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.
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.
These widgets make use of the HTML elements input and textarea.
Date input as a simple text box: <input type='text' ...>
Takes same arguments as TextInput, with one more optional argument:
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.
Date/time input as a simple text box: <input type='text' ...>
Takes same arguments as TextInput, with one more optional argument:
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.
Time input as a simple text box: <input type='text' ...>
Takes same arguments as TextInput, with one more optional argument:
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.
Checkbox: <input type='checkbox' ...>
Takes one optional argument:
A callable that takes the value of the CheckBoxInput and returns True if the checkbox should be checked for that value.
Similar to Select, but rendered as a list of radio buttons within <li> tags:
<ul>
<li><input type='radio' ...></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><input type="radio" name="beatles" value="john" /> John</label>
</div>
<div class="myradio">
<label><input type="radio" name="beatles" value="paul" /> Paul</label>
</div>
<div class="myradio">
<label><input type="radio" name="beatles" value="george" /> George</label>
</div>
<div class="myradio">
<label><input type="radio" name="beatles" value="ringo" /> Ringo</label>
</div>
That included the <label> tags. To get more granular, you can use each radio button’s tag and choice_label attributes. For example, this template...
{% for radio in myform.beatles %}
<label>
{{ radio.choice_label }}
<span class="radio">{{ radio.tag }}</span>
</label>
{% endfor %}
...will result in the following HTML:
<label>
John
<span class="radio"><input type="radio" name="beatles" value="john" /></span>
</label>
<label>
Paul
<span class="radio"><input type="radio" name="beatles" value="paul" /></span>
</label>
<label>
George
<span class="radio"><input type="radio" name="beatles" value="george" /></span>
</label>
<label>
Ringo
<span class="radio"><input type="radio" name="beatles" 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.
Similar to SelectMultiple, but rendered as a list of check buttons:
<ul>
<li><input type='checkbox' ...></li>
...
</ul>
Wrapper (using MultiWidget) around two widgets: DateInput for the date, and TimeInput for the time.
SplitDateTimeWidget has two optional attributes:
Similar to DateInput.format
Similar to TimeInput.format
Wrapper around three 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:
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.
Dec 23, 2012