# documentação Django 2.0.8

# 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')
    'foo@example.com'
    >>> f.clean('invalid email address')
    Traceback (most recent call last):
    ...
    ValidationError: ['Enter a valid email 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:

    >>> from django import forms
    >>> f = forms.CharField()
    >>> f.clean('foo')
    'foo'
    >>> f.clean('')
    Traceback (most recent call last):
    ...
    ValidationError: ['This field is required.']
    >>> f.clean(None)
    Traceback (most recent call last):
    ...
    ValidationError: ['This field is required.']
    >>> f.clean(' ')
    ' '
    >>> f.clean(0)
    '0'
    >>> f.clean(True)
    'True'
    >>> f.clean(False)
    'False'

To specify that a field is not required, pass `required=False` to the `Field` constructor:

    >>> f = forms.CharField(required=False)
    >>> f.clean('foo')
    'foo'
    >>> f.clean('')
    ''
    >>> f.clean(None)
    ''
    >>> f.clean(0)
    '0'
    >>> f.clean(True)
    'True'
    >>> f.clean(False)
    '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 an empty string. For other `Field` classes, it might be `None`. (This varies from field to field.)

Widgets of required form fields have the `required` HTML attribute. Set the `Form.use_required_attribute` attribute to `False` to disable it. The `required` attribute isn’t included on forms of formsets because the browser validation may not be correct when adding and deleting formsets.

### `label`

`Field.``label`

O argumento “label” permite que seja especificado um rótulo “amigável” para este campo. Isto é utilizado quando o “Campo” é renderizado em um “Formulário”.

Como explicado em “Apresentando formulários como HTML” acima, o rótulo padrão para um “Campo” é gerado à partir do nome do campo, convertendo todos underscores em espaços e a primeira letra em maíscula. Especifique “label”, caso este comportamento padrão não resulte em um rótulo adequado.

Aqui está um exemplo completo de um “Form” que implementa “label” de dois de seus campos. Especificamos “auto_id=False” para simplificar a saída:

    >>> from django import forms
    >>> class CommentForm(forms.Form):
    ...     name = forms.CharField(label='Your name')
    ...     url = forms.URLField(label='Your website', required=False)
    ...     comment = forms.CharField()
    >>> f = CommentForm(auto_id=False)
    >>> print(f)
    <tr><th>Your name:</th><td><input type="text" name="name" required /></td></tr>
    <tr><th>Your website:</th><td><input type="url" name="url" /></td></tr>
    <tr><th>Comment:</th><td><input type="text" name="comment" required /></td></tr>

### “label_suffix”

`Field.``label_suffix`

O argumento “label_suffix” permite sobreescrever o atributo ‘attr’ do formulário `label_suffix` em uma ‘per-field basis’:

    >>> class ContactForm(forms.Form):
    ...     age = forms.IntegerField()
    ...     nationality = forms.CharField()
    ...     captcha_answer = forms.IntegerField(label='2 + 2', label_suffix=' =')
    >>> f = ContactForm(label_suffix='?')
    >>> print(f.as_p())
    <p><label for="id_age">Age?</label> <input id="id_age" name="age" type="number" required /></p>
    <p><label for="id_nationality">Nationality?</label> <input id="id_nationality" name="nationality" type="text" required /></p>
    <p><label for="id_captcha_answer">2 + 2 =</label> <input id="id_captcha_answer" name="captcha_answer" type="number" required /></p>

### `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:

    >>> from django import forms
    >>> 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" required /></td></tr>
    <tr><th>Url:</th><td><input type="url" name="url" value="http://" required /></td></tr>
    <tr><th>Comment:</th><td><input type="text" name="comment" required /></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" required /></td></tr>
    <tr><th>Url:</th><td><ul class="errorlist"><li>Enter a valid URL.</li></ul><input type="url" name="url" value="http://" required /></td></tr>
    <tr><th>Comment:</th><td><ul class="errorlist"><li>This field is required.</li></ul><input type="text" name="comment" required /></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': ['This field is required.'], 'name': ['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" required /><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()`).

Like the model field’s `help_text`, this value isn’t HTML-escaped in automatically-generated forms.

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:

    >>> from django import forms
    >>> 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 email 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" required /><br /><span class="helptext">100 characters max.</span></td></tr>
    <tr><th>Message:</th><td><input type="text" name="message" required /></td></tr>
    <tr><th>Sender:</th><td><input type="email" name="sender" required /><br />A valid email 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" required /> <span class="helptext">100 characters max.</span></li>
    <li>Message: <input type="text" name="message" required /></li>
    <li>Sender: <input type="email" name="sender" required /> A valid email 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" required /> <span class="helptext">100 characters max.</span></p>
    <p>Message: <input type="text" name="message" required /></p>
    <p>Sender: <input type="email" name="sender" required /> A valid email 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:

    >>> from django import forms
    >>> generic = forms.CharField()
    >>> generic.clean('')
    Traceback (most recent call last):
      ...
    ValidationError: ['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: ['Please enter your name']

In the built-in Field classes section below, each `Field` defines the error message keys it uses.

### `validators`

`Field.``validators`

The `validators` argument lets you provide a list of validation functions for this field.

See the validators documentation for more information.

### `localize`

`Field.``localize`

The `localize` argument enables the localization of form data input, as well as the rendered output.

See the format localization documentation for more information.

### `disabled`

`Field.``disabled`

The `disabled` boolean argument, when set to `True`, disables a form field using the `disabled` HTML attribute so that it won’t be editable by users. Even if a user tampers with the field’s value submitted to the server, it will be ignored in favor of the value from the form’s initial data.

## Checking if the field data has changed

### `has_changed()`

`Field.``has_changed`()

The `has_changed()` method is used to determine if the field value has changed from the initial value. Returns `True` or `False`.

See the `Form.has_changed()` documentation for more information.

## 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` or `False` value.
  - Validates that the value is `True` (e.g. the check box is checked) if the field has `required=True`.
  - Error message keys: `required`

  Nota

  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: Whatever you’ve given as `empty_value`.
  - Normalizes to: A string.
  - Validates `max_length` or `min_length`, if they are provided. Otherwise, all inputs are valid.
  - Error message keys: `required`, `max_length`, `min_length`

  Has three optional arguments for validation:

  `max_length`
  `min_length`

  If provided, these arguments ensure that the string is at most or at least the given length.

  `strip`

    If `True` (default), the value will be stripped of leading and trailing whitespace.

  `empty_value`
    New in Django 1.11.

    The value to use to represent “empty”. Defaults to an empty string.

### `ChoiceField`

class `ChoiceField`(**kwargs)
  - Default widget: `Select`
  - Empty value: `''` (an empty string)
  - Normalizes to: A string.
  - Validates that the given value exists in the list of choices.
  - Error message keys: `required`, `invalid_choice`

  The `invalid_choice` error message may contain `%(value)s`, which will be replaced with the selected choice.

  Takes one extra argument:

  `choices`

    Either an iterable (e.g., a list or tuple) of 2-tuples to use as choices for this field, or a callable that returns such an iterable. This argument accepts the same formats as the `choices` argument to a model field. See the model field reference documentation on choices for more details. If the argument is a callable, it is evaluated each time the field’s form is initialized. Defaults to an empty list.

### `TypedChoiceField`

class `TypedChoiceField`(**kwargs)

  Just like a `ChoiceField`, except `TypedChoiceField` takes two extra arguments, `coerce` and `empty_value`.

  - Default widget: `Select`
  - Empty value: Whatever you’ve given as `empty_value`.
  - Normalizes to: A value of the type provided by the `coerce` argument.
  - Validates that the given value exists in the list of choices and can be coerced.
  - Error message keys: `required`, `invalid_choice`

  Takes extra arguments:

  `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. Note that coercion happens after input validation, so it is possible to coerce to a value not present in `choices`.

  `empty_value`

    The value to use to represent “empty.” Defaults to the empty string; `None` is another common choice here. Note that this value will not be coerced by the function given in the `coerce` argument, so choose it accordingly.

### `DateField`

class `DateField`(**kwargs)
  - Default widget: `DateInput`
  - 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`

  Takes one optional argument:

  `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',      # '2006-10-25'
       '%m/%d/%Y',      # '10/25/2006'
       '%m/%d/%y']      # '10/25/06'

  Additionally, if you specify `USE_L10N=False` in your settings, the following will also be included in the default input formats:

      ['%b %d %Y',      # 'Oct 25 2006'
       '%b %d, %Y',     # 'Oct 25, 2006'
       '%d %b %Y',      # '25 Oct 2006'
       '%d %b, %Y',     # '25 Oct, 2006'
       '%B %d %Y',      # 'October 25 2006'
       '%B %d, %Y',     # 'October 25, 2006'
       '%d %B %Y',      # '25 October 2006'
       '%d %B, %Y']     # '25 October, 2006'

  See also format localization.

### `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`

  Takes one optional argument:

  `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'

  See also format localization.

### `DecimalField`

class `DecimalField`(**kwargs)
  - Default widget: `NumberInput` when `Field.localize` is `False`, else `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`

  The `max_value` and `min_value` error messages may contain `%(limit_value)s`, which will be substituted by the appropriate limit. Similarly, the `max_digits`, `max_decimal_places` and `max_whole_digits` error messages may contain `%(max)s`.

  Takes four optional arguments:

  `max_value`
  `min_value`

    These control the range of values permitted in the field, and should be given as `decimal.Decimal` values.

  `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.

  `decimal_places`

    The maximum number of decimal places permitted.

### `DurationField`

class `DurationField`(**kwargs)
  - Default widget: `TextInput`
  - Empty value: `None`
  - Normalizes to: A Python `timedelta`.
  - Validates that the given value is a string which can be converted into a `timedelta`.
  - Error message keys: `required`, `invalid`.

  Accepts any format understood by `parse_duration()`.

### `EmailField`

class `EmailField`(**kwargs)
  - Default widget: `EmailInput`
  - Empty value: `''` (an empty string)
  - Normalizes to: A string.
  - Validates that the given value is a valid email address, using a moderately complex regular expression.
  - Error message keys: `required`, `invalid`

  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: `ClearableFileInput`
  - Empty value: `None`
  - Normalizes to: An `UploadedFile` object that wraps the file content and file name into a single object.
  - Can validate that non-empty file data has been bound to the form.
  - Error message keys: `required`, `invalid`, `missing`, `empty`, `max_length`

  Has two optional arguments for validation, `max_length` and `allow_empty_file`. If provided, these ensure that the file name is at most the given length, and that validation will succeed even if the file content is empty.

  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.

  The `max_length` error refers to the length of the filename. In the error message for that key, `%(max)d` will be replaced with the maximum filename length and `%(length)d` will be replaced with the current filename length.

### `FilePathField`

class `FilePathField`(**kwargs)
  - Default widget: `Select`
  - Empty value: `None`
  - Normalizes to: A string.
  - Validates that the selected choice exists in the list of choices.
  - Error message keys: `required`, `invalid_choice`

  The field allows choosing from files inside a certain directory. It takes five extra arguments; only `path` is required:

  `path`

    The absolute path to the directory whose contents you want listed. This directory must exist.

  `recursive`

    If `False` (the default) only the direct contents of `path` will be offered as choices. If `True`, the directory will be descended into recursively and all descendants will be listed as choices.

  `match`

    A regular expression pattern; only files with names matching this expression will be allowed as choices.

  `allow_files`

    Optional. Either `True` or `False`. Default is `True`. Specifies whether files in the specified location should be included. Either this or `allow_folders` must be `True`.

  `allow_folders`

    Optional. Either `True` or `False`. Default is `False`. Specifies whether folders in the specified location should be included. Either this or `allow_files` must be `True`.

### `FloatField`

class `FloatField`(**kwargs)
  - Default widget: `NumberInput` when `Field.localize` is `False`, else `TextInput`.
  - Empty value: `None`
  - Normalizes to: A Python float.
  - Validates that the given value is a 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: `ClearableFileInput`
  - 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 Pillow.
  - Error message keys: `required`, `invalid`, `missing`, `empty`, `invalid_image`

  Using an `ImageField` requires that Pillow is installed with support for the image formats you use. If you encounter a `corrupt image` error when you upload an image, it usually means that Pillow doesn’t understand its format. To fix this, install the appropriate library and reinstall Pillow.

  When you use an `ImageField` on a form, you must also remember to bind the file data to the form.

  After the field has been cleaned and validated, the `UploadedFile` object will have an additional `image` attribute containing the Pillow Image instance used to check if the file was a valid image. Also, `UploadedFile.content_type` will be updated with the image’s content type if Pillow can determine it, otherwise it will be set to `None`.

### `IntegerField`

class `IntegerField`(**kwargs)
  - Default widget: `NumberInput` when `Field.localize` is `False`, else `TextInput`.
  - Empty value: `None`
  - Normalizes to: A Python 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`

  The `max_value` and `min_value` error messages may contain `%(limit_value)s`, which will be substituted by the appropriate limit.

  Takes two optional arguments for validation:

  `max_value`
  `min_value`

  These control the range of values permitted in the field.

### `GenericIPAddressField`

class `GenericIPAddressField`(**kwargs)

  A field containing either an IPv4 or an IPv6 address.

  - Default widget: `TextInput`
  - Empty value: `''` (an empty string)
  - Normalizes to: A string. IPv6 addresses are normalized as described below.
  - Validates that the given value is a valid IP address.
  - Error message keys: `required`, `invalid`

  The IPv6 address normalization follows RFC 4291#section-2.2 section 2.2, including using the IPv4 format suggested in paragraph 3 of that section, like `::ffff:192.0.2.0`. For example, `2001:0::0:01` would be normalized to `2001::1`, and `::ffff:0a0a:0a0a` to `::ffff:10.10.10.10`. All characters are converted to lowercase.

  Takes two optional arguments:

  `protocol`

    Limits valid inputs to the specified protocol. Accepted values are `both` (default), `IPv4` or `IPv6`. Matching is case insensitive.

  `unpack_ipv4`

    Unpacks IPv4 mapped addresses like `::ffff:192.0.2.1`. If this option is enabled that address would be unpacked to `192.0.2.1`. Default is disabled. Can only be used when `protocol` is set to `'both'`.

### `MultipleChoiceField`

class `MultipleChoiceField`(**kwargs)
  - Default widget: `SelectMultiple`
  - Empty value: `[]` (an empty list)
  - Normalizes to: A list of strings.
  - Validates that every value in the given list of values exists in the list of choices.
  - Error message keys: `required`, `invalid_choice`, `invalid_list`

  The `invalid_choice` error message may contain `%(value)s`, which will be replaced with the selected choice.

  Takes one extra required argument, `choices`, as for `ChoiceField`.

### `TypedMultipleChoiceField`

class `TypedMultipleChoiceField`(**kwargs)

  Just like a `MultipleChoiceField`, except `TypedMultipleChoiceField` takes two extra arguments, `coerce` and `empty_value`.

  - Default widget: `SelectMultiple`
  - Empty value: Whatever you’ve given as `empty_value`
  - Normalizes to: A list of values of the type provided by the `coerce` argument.
  - Validates that the given values exists in the list of choices and can be coerced.
  - Error message keys: `required`, `invalid_choice`

  The `invalid_choice` error message may contain `%(value)s`, which will be replaced with the selected choice.

  Takes two extra arguments, `coerce` and `empty_value`, as for `TypedChoiceField`.

### `NullBooleanField`

class `NullBooleanField`(**kwargs)
  - Default widget: `NullBooleanSelect`
  - Empty value: `None`
  - Normalizes to: A Python `True`, `False` or `None` value.
  - Validates nothing (i.e., it never raises a `ValidationError`).

### `RegexField`

class `RegexField`(**kwargs)
  - Default widget: `TextInput`
  - Empty value: `''` (an empty string)
  - Normalizes to: A string.
  - Validates that the given value matches against a certain regular expression.
  - Error message keys: `required`, `invalid`

  Takes one required argument:

  `regex`

    A regular expression specified either as a string or a compiled regular expression object.

  Also takes `max_length`, `min_length`, and `strip`, which work just as they do for `CharField`.

  `strip`

    Defaults to `False`. If enabled, stripping will be applied before the regex validation.

### `SlugField`

class `SlugField`(**kwargs)
  - Default widget: `TextInput`
  - Empty value: `''` (an empty string)
  - Normalizes to: A string.
  - Validates that the given value contains only letters, numbers, underscores, and hyphens.
  - Error messages: `required`, `invalid`

  This field is intended for use in representing a model `SlugField` in forms.

  Takes an optional parameter:

  `allow_unicode`

    A boolean instructing the field to accept Unicode letters in addition to ASCII letters. Defaults to `False`.

### `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`

  Takes one optional argument:

  `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: `URLInput`
  - Empty value: `''` (an empty string)
  - Normalizes to: A string.
  - Validates that the given value is a valid URL.
  - Error message keys: `required`, `invalid`

  Takes the following optional arguments:

  `max_length`
  `min_length`

  These are the same as `CharField.max_length` and `CharField.min_length`.

### `UUIDField`

class `UUIDField`(**kwargs)
  - Default widget: `TextInput`
  - Empty value: `''` (an empty string)
  - Normalizes to: A `UUID` object.
  - Error message keys: `required`, `invalid`

  This field will accept any string format accepted as the `hex` argument to the `UUID` constructor.

## Slightly complex built-in `Field` classes

### `ComboField`

class `ComboField`(**kwargs)
  - Default widget: `TextInput`
  - Empty value: `''` (an empty string)
  - Normalizes to: A string.
  - Validates the given value against each of the fields specified as an argument to the `ComboField`.
  - Error message keys: `required`, `invalid`

  Takes one extra required argument:

  `fields`

    The list of fields that should be used to validate the field’s value (in the order in which they are provided).

        >>> from django.forms import ComboField
        >>> f = ComboField(fields=[CharField(max_length=20), EmailField()])
        >>> f.clean('test@example.com')
        'test@example.com'
        >>> f.clean('longemailaddress@example.com')
        Traceback (most recent call last):
        ...
        ValidationError: ['Ensure this value has at most 20 characters (it has 28).']

### `MultiValueField`

class `MultiValueField`(fields=(), **kwargs)
  - Default widget: `TextInput`
  - Empty value: `''` (an empty string)
  - Normalizes to: the type returned by the `compress` method of the subclass.
  - Validates the given value against each of the fields specified as an argument to the `MultiValueField`.
  - Error message keys: `required`, `invalid`, `incomplete`

  Aggregates the logic of multiple fields that together produce a single value.

  This field is abstract and must be subclassed. In contrast with the single-value fields, subclasses of `MultiValueField` must not implement `clean()` but instead - implement `compress()`.

  Takes one extra required argument:

  `fields`

    A tuple of fields whose values are cleaned and subsequently combined into a single value. Each value of the field is cleaned by the corresponding field in `fields` – the first value is cleaned by the first field, the second value is cleaned by the second field, etc. Once all fields are cleaned, the list of clean values is combined into a single value by `compress()`.

  Also takes some optional arguments:

  `require_all_fields`

    Defaults to `True`, in which case a `required` validation error will be raised if no value is supplied for any field.

    When set to `False`, the `Field.required` attribute can be set to `False` for individual fields to make them optional. If no value is supplied for a required field, an `incomplete` validation error will be raised.

    A default `incomplete` error message can be defined on the `MultiValueField` subclass, or different messages can be defined on each individual field. For example:

        from django.core.validators import RegexValidator

        class PhoneField(MultiValueField):
            def __init__(self, **kwargs):
                # Define one message for all fields.
                error_messages = {
                    'incomplete': 'Enter a country calling code and a phone number.',
                }
                # Or define a different message for each field.
                fields = (
                    CharField(
                        error_messages={'incomplete': 'Enter a country calling code.'},
                        validators=[
                            RegexValidator(r'^[0-9]+$', 'Enter a valid country calling code.'),
                        ],
                    ),
                    CharField(
                        error_messages={'incomplete': 'Enter a phone number.'},
                        validators=[RegexValidator(r'^[0-9]+$', 'Enter a valid phone number.')],
                    ),
                    CharField(
                        validators=[RegexValidator(r'^[0-9]+$', 'Enter a valid extension.')],
                        required=False,
                    ),
                )
                super().__init__(
                    error_messages=error_messages, fields=fields,
                    require_all_fields=False, **kwargs
                )

  `widget`

    Must be a subclass of `django.forms.MultiWidget`. Default value is `TextInput`, which probably is not very useful in this case.

  `compress`(data_list)

    Takes a list of valid values and returns a “compressed” version of those values – in a single value. For example, `SplitDateTimeField` is a subclass which combines a time field and a date field into a `datetime` object.

    This method must be implemented in the subclasses.

### `SplitDateTimeField`

class `SplitDateTimeField`(**kwargs)
  - Default widget: `SplitDateTimeWidget`
  - Empty value: `None`
  - Normalizes to: A Python `datetime.datetime` object.
  - Validates that the given value is a `datetime.datetime` or string formatted in a particular datetime format.
  - Error message keys: `required`, `invalid`, `invalid_date`, `invalid_time`

  Takes two optional arguments:

  `input_date_formats`

    A list of formats used to attempt to convert a string to a valid `datetime.date` object.

  If no `input_date_formats` argument is provided, the default input formats for `DateField` are used.

  `input_time_formats`

    A list of formats used to attempt to convert a string to a valid `datetime.time` object.

  If no `input_time_formats` argument is provided, the default input formats for `TimeField` are used.

## Fields which handle relationships

Two fields are available for representing relationships between models: `ModelChoiceField` and `ModelMultipleChoiceField`. Both of these fields require a single `queryset` parameter that is used to create the choices for the field. Upon form validation, these fields will place either one model object (in the case of `ModelChoiceField`) or multiple model objects (in the case of `ModelMultipleChoiceField`) into the `cleaned_data` dictionary of the form.

For more complex uses, you can specify `queryset=None` when declaring the form field and then populate the `queryset` in the form’s `__init__()` method:

    class FooMultipleChoiceForm(forms.Form):
        foo_select = forms.ModelMultipleChoiceField(queryset=None)

        def __init__(self, *args, **kwargs):
            super().__init__(*args, **kwargs)
            self.fields['foo_select'].queryset = ...

### `ModelChoiceField`

class `ModelChoiceField`(**kwargs)
  - Default widget: `Select`
  - Empty value: `None`
  - Normalizes to: A model instance.
  - Validates that the given id exists in the queryset.
  - Error message keys: `required`, `invalid_choice`

  Allows the selection of a single model object, suitable for representing a foreign key. Note that the default widget for `ModelChoiceField` becomes impractical when the number of entries increases. You should avoid using it for more than 100 items.

  A single argument is required:

  `queryset`

    A `QuerySet` of model objects from which the choices for the field are derived and which is used to validate the user’s selection. It’s evaluated when the form is rendered.

  `ModelChoiceField` also takes two optional arguments:

  `empty_label`

    By default the `<select>` widget used by `ModelChoiceField` will have an empty choice at the top of the list. You can change the text of this label (which is `"---------"` by default) with the `empty_label` attribute, or you can disable the empty label entirely by setting `empty_label` to `None`:

        # 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 of `empty_label`).

  `to_field_name`

    This optional argument is used to specify the field to use as the value of the choices in the field’s widget. Be sure it’s a unique field for the model, otherwise the selected value could match more than one object. By default it is set to `None`, in which case the primary key of each object will be used. For example:

        # No custom to_field_name
        field1 = forms.ModelChoiceField(queryset=...)

    would yield:

        <select id="id_field1" name="field1">
        <option value="obj1.pk">Object1</option>
        <option value="obj2.pk">Object2</option>
        ...
        </select>

    and:

        # to_field_name provided
        field2 = forms.ModelChoiceField(queryset=..., to_field_name="name")

    would yield:

        <select id="id_field2" name="field2">
        <option value="obj1.name">Object1</option>
        <option value="obj2.name">Object2</option>
        ...
        </select>

  The `__str__()` 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:

      from django.forms import ModelChoiceField

      class MyModelChoiceField(ModelChoiceField):
          def label_from_instance(self, obj):
              return "My Object #%i" % obj.id

### `ModelMultipleChoiceField`

class `ModelMultipleChoiceField`(**kwargs)
  - Default widget: `SelectMultiple`
  - Empty value: An empty `QuerySet` (self.queryset.none())
  - Normalizes to: A `QuerySet` of model instances.
  - Validates that every id in the given list of values exists in the queryset.
  - Error message keys: `required`, `list`, `invalid_choice`, `invalid_pk_value`

  The `invalid_choice` message may contain `%(value)s` and the `invalid_pk_value` message may contain `%(pk)s`, which will be substituted by the appropriate values.

  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.

  A single argument is required:

  `queryset`

    Same as `ModelChoiceField.queryset`.

  Takes one optional argument:

  `to_field_name`

    Same as `ModelChoiceField.to_field_name`.

## 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`).

You can also customize how a field will be accessed by overriding `get_bound_field()`.