Form fields¶
-
class
Field
(**kwargs)¶
When you create a Form
class, the most important part is defining the
fields of the form. Each field has custom validation logic, along with a few
other hooks.
-
Field.
clean
(value)¶
Although the primary way you’ll use Field
classes is in Form
classes,
you can also instantiate them and use them directly to get a better idea of
how they work. Each Field
instance has a clean()
method, which takes
a single argument and either raises a django.forms.ValidationError
exception or returns the clean value:
>>> from django import forms
>>> f = forms.EmailField()
>>> f.clean('foo@example.com')
u'foo@example.com'
>>> f.clean(u'foo@example.com')
u'foo@example.com'
>>> f.clean('invalid e-mail address')
Traceback (most recent call last):
...
ValidationError: [u'Enter a valid e-mail address.']
Core field arguments¶
Each Field
class constructor takes at least these arguments. Some
Field
classes take additional, field-specific arguments, but the following
should always be accepted:
required
¶
-
Field.
required
¶
By default, each Field
class assumes the value is required, so if you pass
an empty value – either None
or the empty string (""
) – then
clean()
will raise a ValidationError
exception:
>>> f = forms.CharField()
>>> f.clean('foo')
u'foo'
>>> f.clean('')
Traceback (most recent call last):
...
ValidationError: [u'This field is required.']
>>> f.clean(None)
Traceback (most recent call last):
...
ValidationError: [u'This field is required.']
>>> f.clean(' ')
u' '
>>> f.clean(0)
u'0'
>>> f.clean(True)
u'True'
>>> f.clean(False)
u'False'
To specify that a field is not required, pass required=False
to the
Field
constructor:
>>> f = forms.CharField(required=False)
>>> f.clean('foo')
u'foo'
>>> f.clean('')
u''
>>> f.clean(None)
u''
>>> f.clean(0)
u'0'
>>> f.clean(True)
u'True'
>>> f.clean(False)
u'False'
If a Field
has required=False
and you pass clean()
an empty value,
then clean()
will return a normalized empty value rather than raising
ValidationError
. For CharField
, this will be a Unicode empty string.
For other Field
classes, it might be None
. (This varies from field to
field.)
label
¶
-
Field.
label
¶
The label
argument lets you specify the “human-friendly” label for this
field. This is used when the Field
is displayed in a Form
.
As explained in “Outputting forms as HTML” above, the default label for a
Field
is generated from the field name by converting all underscores to
spaces and upper-casing the first letter. Specify label
if that default
behavior doesn’t result in an adequate label.
Here’s a full example Form
that implements label
for two of its fields.
We’ve specified auto_id=False
to simplify the output:
>>> class CommentForm(forms.Form):
... name = forms.CharField(label='Your name')
... url = forms.URLField(label='Your Web site', required=False)
... comment = forms.CharField()
>>> f = CommentForm(auto_id=False)
>>> print f
<tr><th>Your name:</th><td><input type="text" name="name" /></td></tr>
<tr><th>Your Web site:</th><td><input type="text" name="url" /></td></tr>
<tr><th>Comment:</th><td><input type="text" name="comment" /></td></tr>
initial
¶
-
Field.
initial
¶
The initial
argument lets you specify the initial value to use when
rendering this Field
in an unbound Form
.
To specify dynamic initial data, see the Form.initial
parameter.
The use-case for this is when you want to display an “empty” form in which a field is initialized to a particular value. For example:
>>> class CommentForm(forms.Form):
... name = forms.CharField(initial='Your name')
... url = forms.URLField(initial='http://')
... comment = forms.CharField()
>>> f = CommentForm(auto_id=False)
>>> print f
<tr><th>Name:</th><td><input type="text" name="name" value="Your name" /></td></tr>
<tr><th>Url:</th><td><input type="text" name="url" value="http://" /></td></tr>
<tr><th>Comment:</th><td><input type="text" name="comment" /></td></tr>
You may be thinking, why not just pass a dictionary of the initial values as data when displaying the form? Well, if you do that, you’ll trigger validation, and the HTML output will include any validation errors:
>>> class CommentForm(forms.Form):
... name = forms.CharField()
... url = forms.URLField()
... comment = forms.CharField()
>>> default_data = {'name': 'Your name', 'url': 'http://'}
>>> f = CommentForm(default_data, auto_id=False)
>>> print f
<tr><th>Name:</th><td><input type="text" name="name" value="Your name" /></td></tr>
<tr><th>Url:</th><td><ul class="errorlist"><li>Enter a valid URL.</li></ul><input type="text" name="url" value="http://" /></td></tr>
<tr><th>Comment:</th><td><ul class="errorlist"><li>This field is required.</li></ul><input type="text" name="comment" /></td></tr>
This is why initial
values are only displayed for unbound forms. For bound
forms, the HTML output will use the bound data.
Also note that initial
values are not used as “fallback” data in
validation if a particular field’s value is not given. initial
values are
only intended for initial form display:
>>> class CommentForm(forms.Form):
... name = forms.CharField(initial='Your name')
... url = forms.URLField(initial='http://')
... comment = forms.CharField()
>>> data = {'name': '', 'url': '', 'comment': 'Foo'}
>>> f = CommentForm(data)
>>> f.is_valid()
False
# The form does *not* fall back to using the initial values.
>>> f.errors
{'url': [u'This field is required.'], 'name': [u'This field is required.']}
Instead of a constant, you can also pass any callable:
>>> import datetime
>>> class DateForm(forms.Form):
... day = forms.DateField(initial=datetime.date.today)
>>> print DateForm()
<tr><th>Day:</th><td><input type="text" name="day" value="12/23/2008" /><td></tr>
The callable will be evaluated only when the unbound form is displayed, not when it is defined.
widget
¶
-
Field.
widget
¶
The widget
argument lets you specify a Widget
class to use when
rendering this Field
. See Widgets for more information.
help_text
¶
-
Field.
help_text
¶
The help_text
argument lets you specify descriptive text for this
Field
. If you provide help_text
, it will be displayed next to the
Field
when the Field
is rendered by one of the convenience Form
methods (e.g., as_ul()
).
Here’s a full example Form
that implements help_text
for two of its
fields. We’ve specified auto_id=False
to simplify the output:
>>> class HelpTextContactForm(forms.Form):
... subject = forms.CharField(max_length=100, help_text='100 characters max.')
... message = forms.CharField()
... sender = forms.EmailField(help_text='A valid e-mail address, please.')
... cc_myself = forms.BooleanField(required=False)
>>> f = HelpTextContactForm(auto_id=False)
>>> print f.as_table()
<tr><th>Subject:</th><td><input type="text" name="subject" maxlength="100" /><br />100 characters max.</td></tr>
<tr><th>Message:</th><td><input type="text" name="message" /></td></tr>
<tr><th>Sender:</th><td><input type="text" name="sender" /><br />A valid e-mail address, please.</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" /> 100 characters max.</li>
<li>Message: <input type="text" name="message" /></li>
<li>Sender: <input type="text" name="sender" /> A valid e-mail address, please.</li>
<li>Cc myself: <input type="checkbox" name="cc_myself" /></li>
>>> print f.as_p()
<p>Subject: <input type="text" name="subject" maxlength="100" /> 100 characters max.</p>
<p>Message: <input type="text" name="message" /></p>
<p>Sender: <input type="text" name="sender" /> A valid e-mail address, please.</p>
<p>Cc myself: <input type="checkbox" name="cc_myself" /></p>
error_messages
¶
-
Field.
error_messages
¶
The error_messages
argument lets you override the default messages that the
field will raise. Pass in a dictionary with keys matching the error messages you
want to override. For example, here is the default error message:
>>> generic = forms.CharField()
>>> generic.clean('')
Traceback (most recent call last):
...
ValidationError: [u'This field is required.']
And here is a custom error message:
>>> name = forms.CharField(error_messages={'required': 'Please enter your name'})
>>> name.clean('')
Traceback (most recent call last):
...
ValidationError: [u'Please enter your name']
In the built-in Field classes section below, each Field
defines the
error message keys it uses.
Built-in Field
classes¶
Naturally, the forms
library comes with a set of Field
classes that
represent common validation needs. This section documents each built-in field.
For each field, we describe the default widget used if you don’t specify
widget
. We also specify the value returned when you provide an empty value
(see the section on required
above to understand what that means).
BooleanField
¶
-
class
BooleanField
(**kwargs)¶ - Default widget:
CheckboxInput
- Empty value:
False
- Normalizes to: A Python
True
orFalse
value. - Validates that the value is
True
(e.g. the check box is checked) if the field hasrequired=True
. - Error message keys:
required
- Default widget:
CheckboxInput
(and hence the standard
BooleanField
) has changed to return False
instead of None
in
the Django 1.0.Note
Since all Field
subclasses have required=True
by default, the
validation condition here is important. If you want to include a boolean
in your form that can be either True
or False
(e.g. a checked or
unchecked checkbox), you must remember to pass in required=False
when
creating the BooleanField
.
CharField
¶
-
class
CharField
(**kwargs)¶ - Default widget:
TextInput
- Empty value:
''
(an empty string) - Normalizes to: A Unicode object.
- Validates
max_length
ormin_length
, if they are provided. Otherwise, all inputs are valid. - Error message keys:
required
,max_length
,min_length
- Default widget:
Has two optional arguments for validation:
-
CharField.
max_length
¶
-
CharField.
min_length
¶ If provided, these arguments ensure that the string is at most or at least the given length.
ChoiceField
¶
-
class
ChoiceField
(**kwargs)¶ - Default widget:
Select
- Empty value:
''
(an empty string) - Normalizes to: A Unicode object.
- Validates that the given value exists in the list of choices.
- Error message keys:
required
,invalid_choice
- Default widget:
Takes one extra required argument:
-
ChoiceField.
choices
¶ An iterable (e.g., a list or tuple) of 2-tuples to use as choices for this field.
TypedChoiceField
¶
-
class
TypedChoiceField
(**kwargs)¶
Just like a ChoiceField
, except TypedChoiceField
takes an
extra coerce
argument.
- Default widget:
Select
- Empty value: Whatever you’ve given as
empty_value
- Normalizes to: the value returned by the
coerce
argument. - Validates that the given value exists in the list of choices.
- Error message keys:
required
,invalid_choice
Takes extra arguments:
-
TypedChoiceField.
coerce
¶ A function that takes one argument and returns a coerced value. Examples include the built-in
int
,float
,bool
and other types. Defaults to an identity function.
-
TypedChoiceField.
empty_value
¶ The value to use to represent “empty.” Defaults to the empty string;
None
is another common choice here.
DateField
¶
-
class
DateField
(**kwargs)¶ - Default widget:
TextInput
- Empty value:
None
- Normalizes to: A Python
datetime.date
object. - Validates that the given value is either a
datetime.date
,datetime.datetime
or string formatted in a particular date format. - Error message keys:
required
,invalid
- Default widget:
Takes one optional argument:
-
DateField.
input_formats
¶ A list of formats used to attempt to convert a string to a valid
datetime.date
object.
If no input_formats
argument is provided, the default input formats are:
'%Y-%m-%d', '%m/%d/%Y', '%m/%d/%y', # '2006-10-25', '10/25/2006', '10/25/06'
'%b %d %Y', '%b %d, %Y', # 'Oct 25 2006', 'Oct 25, 2006'
'%d %b %Y', '%d %b, %Y', # '25 Oct 2006', '25 Oct, 2006'
'%B %d %Y', '%B %d, %Y', # 'October 25 2006', 'October 25, 2006'
'%d %B %Y', '%d %B, %Y', # '25 October 2006', '25 October, 2006'
DateTimeField
¶
-
class
DateTimeField
(**kwargs)¶ - Default widget:
DateTimeInput
- Empty value:
None
- Normalizes to: A Python
datetime.datetime
object. - Validates that the given value is either a
datetime.datetime
,datetime.date
or string formatted in a particular datetime format. - Error message keys:
required
,invalid
- Default widget:
Takes one optional argument:
-
DateTimeField.
input_formats
¶ A list of formats used to attempt to convert a string to a valid
datetime.datetime
object.
If no input_formats
argument is provided, the default input formats are:
'%Y-%m-%d %H:%M:%S', # '2006-10-25 14:30:59'
'%Y-%m-%d %H:%M', # '2006-10-25 14:30'
'%Y-%m-%d', # '2006-10-25'
'%m/%d/%Y %H:%M:%S', # '10/25/2006 14:30:59'
'%m/%d/%Y %H:%M', # '10/25/2006 14:30'
'%m/%d/%Y', # '10/25/2006'
'%m/%d/%y %H:%M:%S', # '10/25/06 14:30:59'
'%m/%d/%y %H:%M', # '10/25/06 14:30'
'%m/%d/%y', # '10/25/06'
DateTimeField
used to use a TextInput
widget by default. This has now changed.DecimalField
¶
-
class
DecimalField
(**kwargs)¶ - Default widget:
TextInput
- Empty value:
None
- Normalizes to: A Python
decimal
. - Validates that the given value is a decimal. Leading and trailing whitespace is ignored.
- Error message keys:
required
,invalid
,max_value
,min_value
,max_digits
,max_decimal_places
,max_whole_digits
- Default widget:
Takes four optional arguments:
-
DecimalField.
max_value
¶
-
DecimalField.
min_value
¶ These attributes define the limits for the fields value.
-
DecimalField.
max_digits
¶ The maximum number of digits (those before the decimal point plus those after the decimal point, with leading zeros stripped) permitted in the value.
-
DecimalField.
decimal_places
¶ The maximum number of decimal places permitted.
EmailField
¶
-
class
EmailField
(**kwargs)¶ - Default widget:
TextInput
- Empty value:
''
(an empty string) - Normalizes to: A Unicode object.
- Validates that the given value is a valid e-mail address, using a moderately complex regular expression.
- Error message keys:
required
,invalid
- Default widget:
Has two optional arguments for validation, max_length
and min_length
.
If provided, these arguments ensure that the string is at most or at least the
given length.
FileField
¶
-
class
FileField
(**kwargs)¶ - Default widget:
FileInput
- Empty value:
None
- Normalizes to: An
UploadedFile
object that wraps the file content and file name into a single object. - Validates that non-empty file data has been bound to the form.
- Error message keys:
required
,invalid
,missing
,empty
- Default widget:
To learn more about the UploadedFile
object, see the file uploads
documentation.
When you use a FileField
in a form, you must also remember to
bind the file data to the form.
FilePathField
¶
-
class
FilePathField
(**kwargs)¶ - Default widget:
Select
- Empty value:
None
- Normalizes to: A unicode object
- Validates that the selected choice exists in the list of choices.
- Error message keys:
required
,invalid_choice
- Default widget:
The field allows choosing from files inside a certain directory. It takes three
extra arguments; only path
is required:
-
FilePathField.
path
¶ The absolute path to the directory whose contents you want listed. This directory must exist.
-
FilePathField.
recursive
¶ If
False
(the default) only the direct contents ofpath
will be offered as choices. IfTrue
, the directory will be descended into recursively and all descendants will be listed as choices.
-
FilePathField.
match
¶ A regular expression pattern; only files with names matching this expression will be allowed as choices.
FloatField
¶
- Default widget:
TextInput
- Empty value:
None
- Normalizes to: A Python float.
- Validates that the given value is an float. Leading and trailing
whitespace is allowed, as in Python’s
float()
function. - Error message keys:
required
,invalid
,max_value
,min_value
Takes two optional arguments for validation, max_value
and min_value
.
These control the range of values permitted in the field.
ImageField
¶
-
class
ImageField
(**kwargs)¶ - Default widget:
FileInput
- Empty value:
None
- Normalizes to: An
UploadedFile
object that wraps the file content and file name into a single object. - Validates that file data has been bound to the form, and that the file is of an image format understood by PIL.
- Error message keys:
required
,invalid
,missing
,empty
,invalid_image
- Default widget:
Using an ImageField requires that the Python Imaging Library is installed.
When you use an ImageField
on a form, you must also remember to
bind the file data to the form.
IntegerField
¶
-
class
IntegerField
(**kwargs)¶ - Default widget:
TextInput
- Empty value:
None
- Normalizes to: A Python integer or long integer.
- Validates that the given value is an integer. Leading and trailing
whitespace is allowed, as in Python’s
int()
function. - Error message keys:
required
,invalid
,max_value
,min_value
- Default widget:
Takes two optional arguments for validation:
-
IntegerField.
max_value
¶
-
IntegerField.
min_value
¶ These control the range of values permitted in the field.
IPAddressField
¶
-
class
IPAddressField
(**kwargs)¶ - Default widget:
TextInput
- Empty value:
''
(an empty string) - Normalizes to: A Unicode object.
- Validates that the given value is a valid IPv4 address, using a regular expression.
- Error message keys:
required
,invalid
- Default widget:
MultipleChoiceField
¶
-
class
MultipleChoiceField
(**kwargs)¶ - Default widget:
SelectMultiple
- Empty value:
[]
(an empty list) - Normalizes to: A list of Unicode objects.
- Validates that every value in the given list of values exists in the list of choices.
- Error message keys:
required
,invalid_choice
,invalid_list
- Default widget:
Takes one extra argument, choices
, as for ChoiceField
.
NullBooleanField
¶
-
class
NullBooleanField
(**kwargs)¶ - Default widget:
NullBooleanSelect
- Empty value:
None
- Normalizes to: A Python
True
,False
orNone
value. - Validates nothing (i.e., it never raises a
ValidationError
).
- Default widget:
RegexField
¶
-
class
RegexField
(**kwargs)¶ - Default widget:
TextInput
- Empty value:
''
(an empty string) - Normalizes to: A Unicode object.
- Validates that the given value matches against a certain regular expression.
- Error message keys:
required
,invalid
- Default widget:
Takes one required argument:
-
RegexField.
regex
¶ A regular expression specified either as a string or a compiled regular expression object.
Also takes max_length
and min_length
, which work just as they do for
CharField
.
The optional argument error_message
is also accepted for backwards
compatibility. The preferred way to provide an error message is to use the
error_messages
argument, passing a dictionary with 'invalid'
as a key
and the error message as the value.
TimeField
¶
-
class
TimeField
(**kwargs)¶ - Default widget:
TextInput
- Empty value:
None
- Normalizes to: A Python
datetime.time
object. - Validates that the given value is either a
datetime.time
or string formatted in a particular time format. - Error message keys:
required
,invalid
- Default widget:
Takes one optional argument:
-
TimeField.
input_formats
¶ A list of formats used to attempt to convert a string to a valid
datetime.time
object.
If no input_formats
argument is provided, the default input formats are:
'%H:%M:%S', # '14:30:59'
'%H:%M', # '14:30'
URLField
¶
-
class
URLField
(**kwargs)¶ - Default widget:
TextInput
- Empty value:
''
(an empty string) - Normalizes to: A Unicode object.
- Validates that the given value is a valid URL.
- Error message keys:
required
,invalid
,invalid_link
- Default widget:
Takes the following optional arguments:
-
URLField.
max_length
¶
-
URLField.
min_length
¶ Same as
CharField.max_length
andCharField.min_length
.
-
URLField.
verify_exists
¶ If
True
, the validator will attempt to load the given URL, raisingValidationError
if the page gives a 404. Defaults toFalse
.
-
URLField.
validator_user_agent
¶ String used as the user-agent used when checking for a URL’s existence. Defaults to the value of the
URL_VALIDATOR_USER_AGENT
setting.
Slightly complex built-in Field
classes¶
The following are not yet documented.
-
class
ComboField
(**kwargs)¶
-
class
MultiValueField
(**kwargs)¶
-
class
SplitDateTimeField
(**kwargs)¶
Fields which handle relationships¶
For representing relationships between models, two fields are
provided which can derive their choices from a QuerySet
:
-
class
ModelChoiceField
(**kwargs)¶
-
class
ModelMultipleChoiceField
(**kwargs)¶
These fields place one or more model objects into the cleaned_data
dictionary of forms in which they’re used. Both of these fields have an
additional required argument:
-
ModelChoiceField.
queryset
¶ A
QuerySet
of model objects from which the choices for the field will be derived, and which will be used to validate the user’s selection.
ModelChoiceField
¶
Allows the selection of a single model object, suitable for representing a foreign key.
The __unicode__
method of the model will be called to generate
string representations of the objects for use in the field’s choices;
to provide customized representations, subclass ModelChoiceField
and override label_from_instance
. This method will receive a model
object, and should return a string suitable for representing it. For
example:
class MyModelChoiceField(ModelChoiceField):
def label_from_instance(self, obj):
return "My Object #%i" % obj.id
-
ModelChoiceField.
empty_label
¶ By default the
<select>
widget used byModelChoiceField
will have a an empty choice at the top of the list. You can change the text of this label (which is"---------"
by default) with theempty_label
attribute, or you can disable the empty label entirely by settingempty_label
toNone
:# A custom empty label field1 = forms.ModelChoiceField(queryset=..., empty_label="(Nothing)") # No empty label field2 = forms.ModelChoiceField(queryset=..., empty_label=None)
Note that if a
ModelChoiceField
is required and has a default initial value, no empty choice is created (regardless of the value ofempty_label
).
ModelMultipleChoiceField
¶
Allows the selection of one or more model objects, suitable for
representing a many-to-many relation. As with ModelChoiceField
,
you can use label_from_instance
to customize the object
representations.
Creating custom fields¶
If the built-in Field
classes don’t meet your needs, you can easily create
custom Field
classes. To do this, just create a subclass of
django.forms.Field
. Its only requirements are that it implement a
clean()
method and that its __init__()
method accept the core arguments
mentioned above (required
, label
, initial
, widget
,
help_text
).