Viewing github.com/django/django-stable-4.1.x/docs/ref/validators.txt

```
==========
```
```
Validators
```
```
==========
```
```
.. module:: django.core.validators
```

    :synopsis: Validation utilities and base classes

```
Writing validators
```
```
==================
```

A validator is a callable that takes a value and raises a

:exc:`~django.core.exceptions.ValidationError` if it doesn't meet some

criteria. Validators can be useful for reusing validation logic between

```
different types of fields.
```

For example, here's a validator that only allows even numbers::

    from django.core.exceptions import ValidationError

    from django.utils.translation import gettext_lazy as _

```
    def validate_even(value):
```
```
        if value % 2 != 0:
```
```
            raise ValidationError(
```

                _('%(value)s is not an even number'),

                params={'value': value},

```
            )
```

You can add this to a model field via the field's :attr:`~django.db.models.Field.validators`

```
argument::
```
```
    from django.db import models
```
```
    class MyModel(models.Model):
```

        even_field = models.IntegerField(validators=[validate_even])

Because values are converted to Python before validators are run, you can even

```
use the same validator with forms::
```
```
    from django import forms
```
```
    class MyForm(forms.Form):
```

        even_field = forms.IntegerField(validators=[validate_even])

You can also use a class with a ``__call__()`` method for more complex or

configurable validators. :class:`RegexValidator`, for example, uses this

technique. If a class-based validator is used in the

:attr:`~django.db.models.Field.validators` model field option, you should make

sure it is :ref:`serializable by the migration framework

<migration-serializing>` by adding :ref:`deconstruct()

<custom-deconstruct-method>` and ``__eq__()`` methods.

```
How validators are run
```
```
======================
```

See the :doc:`form validation </ref/forms/validation>` for more information on

how validators are run in forms, and :ref:`Validating objects

<validating-objects>` for how they're run in models. Note that validators will

not be run automatically when you save a model, but if you are using a

:class:`~django.forms.ModelForm`, it will run your validators on any fields

that are included in your form. See the

:doc:`ModelForm documentation </topics/forms/modelforms>` for information on

how model validation interacts with forms.

```
Built-in validators
```
```
===================
```

The :mod:`django.core.validators` module contains a collection of callable

validators for use with model and form fields. They're used internally but

are available for use with your own fields, too. They can be used in addition

to, or in lieu of custom ``field.clean()`` methods.

```
``RegexValidator``
```
```
------------------
```

.. class:: RegexValidator(regex=None, message=None, code=None, inverse_match=None, flags=0)

    :param regex: If not ``None``, overrides :attr:`regex`. Can be a regular

        expression string or a pre-compiled regular expression.

    :param message: If not ``None``, overrides :attr:`.message`.

    :param code: If not ``None``, overrides :attr:`code`.

    :param inverse_match: If not ``None``, overrides :attr:`inverse_match`.

    :param flags: If not ``None``, overrides :attr:`flags`. In that case,

        :attr:`regex` must be a regular expression string, or

```
        :exc:`TypeError` is raised.
```

    A :class:`RegexValidator` searches the provided ``value`` for a given

    regular expression with :func:`re.search`. By default, raises a

    :exc:`~django.core.exceptions.ValidationError` with :attr:`message` and

    :attr:`code` if a match **is not** found. Its behavior can be inverted by

    setting :attr:`inverse_match` to ``True``, in which case the

    :exc:`~django.core.exceptions.ValidationError` is raised when a match

```
    **is** found.
```
```
    .. attribute:: regex
```

        The regular expression pattern to search for within the provided

        ``value``, using :func:`re.search`. This may be a string or a

        pre-compiled regular expression created with :func:`re.compile`.

        Defaults to the empty string, which will be found in every possible

```
        ``value``.
```
```
    .. attribute:: message
```
```
        The error message used by
```

        :exc:`~django.core.exceptions.ValidationError` if validation fails.

        Defaults to ``"Enter a valid value"``.

```
    .. attribute:: code
```

        The error code used by :exc:`~django.core.exceptions.ValidationError`

        if validation fails. Defaults to ``"invalid"``.

```
    .. attribute:: inverse_match
```

        The match mode for :attr:`regex`. Defaults to ``False``.

```
    .. attribute:: flags
```

        The :ref:`regex flags <python:contents-of-module-re>` used when

        compiling the regular expression string :attr:`regex`. If :attr:`regex`

        is a pre-compiled regular expression, and :attr:`flags` is overridden,

        :exc:`TypeError` is raised. Defaults to ``0``.

```
``EmailValidator``
```
```
------------------
```

.. class:: EmailValidator(message=None, code=None, allowlist=None)

    :param message: If not ``None``, overrides :attr:`.message`.

    :param code: If not ``None``, overrides :attr:`code`.

    :param allowlist: If not ``None``, overrides :attr:`allowlist`.

    An :class:`EmailValidator` ensures that a value looks like an email, and

    raises a :exc:`~django.core.exceptions.ValidationError` with

    :attr:`message` and :attr:`code` if it doesn't. Values longer than 320

    characters are always considered invalid.

```
    .. attribute:: message
```
```
        The error message used by
```

        :exc:`~django.core.exceptions.ValidationError` if validation fails.

        Defaults to ``"Enter a valid email address"``.

```
    .. attribute:: code
```

        The error code used by :exc:`~django.core.exceptions.ValidationError`

        if validation fails. Defaults to ``"invalid"``.

```
    .. attribute:: allowlist
```

        Allowlist of email domains. By default, a regular expression (the

        ``domain_regex`` attribute) is used to validate whatever appears after

        the ``@`` sign. However, if that string appears in the ``allowlist``,

        this validation is bypassed. If not provided, the default ``allowlist``

        is ``['localhost']``. Other domains that don't contain a dot won't pass

        validation, so you'd need to add them to the ``allowlist`` as

```
        necessary.
```
```
    .. versionchanged:: 3.2.20
```

        In older versions, values longer than 320 characters could be

```
        considered valid.
```
```
``URLValidator``
```
```
----------------
```

.. class:: URLValidator(schemes=None, regex=None, message=None, code=None)

    A :class:`RegexValidator` subclass that ensures a value looks like a URL,

    and raises an error code of ``'invalid'`` if it doesn't. Values longer than

    :attr:`max_length` characters are always considered invalid.

    Loopback addresses and reserved IP spaces are considered valid. Literal

    IPv6 addresses (:rfc:`3986#section-3.2.2`) and Unicode domains are both

```
    supported.
```

    In addition to the optional arguments of its parent :class:`RegexValidator`

    class, ``URLValidator`` accepts an extra optional attribute:

```
    .. attribute:: schemes
```

        URL/URI scheme list to validate against. If not provided, the default

        list is ``['http', 'https', 'ftp', 'ftps']``. As a reference, the IANA

        website provides a full list of `valid URI schemes`_.

        .. _valid URI schemes: https://www.iana.org/assignments/uri-schemes/uri-schemes.xhtml

```
    .. attribute:: max_length
```
```
        .. versionadded:: 3.2.20
```

        The maximum length of values that could be considered valid. Defaults

```
        to 2048 characters.
```
```
    .. versionchanged:: 3.2.20
```

        In older versions, values longer than 2048 characters could be

```
        considered valid.
```
```
``validate_email``
```
```
------------------
```
```
.. data:: validate_email
```

    An :class:`EmailValidator` instance without any customizations.

```
``validate_slug``
```
```
-----------------
```
```
.. data:: validate_slug
```

    A :class:`RegexValidator` instance that ensures a value consists of only

    letters, numbers, underscores or hyphens.

```
``validate_unicode_slug``
```
```
-------------------------
```
```
.. data:: validate_unicode_slug
```

    A :class:`RegexValidator` instance that ensures a value consists of only

    Unicode letters, numbers, underscores, or hyphens.

```
``validate_ipv4_address``
```
```
-------------------------
```
```
.. data:: validate_ipv4_address
```

    A :class:`RegexValidator` instance that ensures a value looks like an IPv4

```
    address.
```
```
``validate_ipv6_address``
```
```
-------------------------
```
```
.. data:: validate_ipv6_address
```

    Uses ``django.utils.ipv6`` to check the validity of an IPv6 address.

```
``validate_ipv46_address``
```
```
--------------------------
```
```
.. data:: validate_ipv46_address
```

    Uses both ``validate_ipv4_address`` and ``validate_ipv6_address`` to

    ensure a value is either a valid IPv4 or IPv6 address.

``validate_comma_separated_integer_list``

-----------------------------------------

.. data:: validate_comma_separated_integer_list

    A :class:`RegexValidator` instance that ensures a value is a

```
    comma-separated list of integers.
```
```
``int_list_validator``
```
```
----------------------
```

.. function:: int_list_validator(sep=',', message=None, code='invalid', allow_negative=False)

    Returns a :class:`RegexValidator` instance that ensures a string consists

    of integers separated by ``sep``. It allows negative integers when

```
    ``allow_negative`` is ``True``.
```
```
``MaxValueValidator``
```
```
---------------------
```

.. class:: MaxValueValidator(limit_value, message=None)

    Raises a :exc:`~django.core.exceptions.ValidationError` with a code of

    ``'max_value'`` if ``value`` is greater than ``limit_value``, which may be

```
    a callable.
```
```
``MinValueValidator``
```
```
---------------------
```

.. class:: MinValueValidator(limit_value, message=None)

    Raises a :exc:`~django.core.exceptions.ValidationError` with a code of

    ``'min_value'`` if ``value`` is less than ``limit_value``, which may be a

```
    callable.
```
```
``MaxLengthValidator``
```
```
----------------------
```

.. class:: MaxLengthValidator(limit_value, message=None)

    Raises a :exc:`~django.core.exceptions.ValidationError` with a code of

    ``'max_length'`` if the length of ``value`` is greater than

    ``limit_value``, which may be a callable.

```
``MinLengthValidator``
```
```
----------------------
```

.. class:: MinLengthValidator(limit_value, message=None)

    Raises a :exc:`~django.core.exceptions.ValidationError` with a code of

    ``'min_length'`` if the length of ``value`` is less than ``limit_value``,

```
    which may be a callable.
```
```
``DecimalValidator``
```
```
--------------------
```

.. class:: DecimalValidator(max_digits, decimal_places)

    Raises :exc:`~django.core.exceptions.ValidationError` with the following

```
    codes:
```

    - ``'max_digits'`` if the number of digits is larger than ``max_digits``.

    - ``'max_decimal_places'`` if the number of decimals is larger than

```
      ``decimal_places``.
```

    - ``'max_whole_digits'`` if the number of whole digits is larger than

      the difference between ``max_digits`` and ``decimal_places``.

```
``FileExtensionValidator``
```
```
--------------------------
```

.. class:: FileExtensionValidator(allowed_extensions, message, code)

    Raises a :exc:`~django.core.exceptions.ValidationError` with a code of

    ``'invalid_extension'`` if the extension of ``value.name`` (``value`` is

    a :class:`~django.core.files.File`) isn't found in ``allowed_extensions``.

    The extension is compared case-insensitively with ``allowed_extensions``.

```
    .. warning::
```

        Don't rely on validation of the file extension to determine a file's

        type. Files can be renamed to have any extension no matter what data

```
        they contain.
```
```
``validate_image_file_extension``
```
```
---------------------------------
```

.. data:: validate_image_file_extension

    Uses Pillow to ensure that ``value.name`` (``value`` is a

    :class:`~django.core.files.File`) has `a valid image extension

    <https://pillow.readthedocs.io/en/latest/handbook/image-file-formats.html>`_.

```
``ProhibitNullCharactersValidator``
```
```
-----------------------------------
```

.. class:: ProhibitNullCharactersValidator(message=None, code=None)

    Raises a :exc:`~django.core.exceptions.ValidationError` if ``str(value)``

    contains one or more null characters (``'\x00'``).

    :param message: If not ``None``, overrides :attr:`.message`.

    :param code: If not ``None``, overrides :attr:`code`.

```
    .. attribute:: message
```
```
        The error message used by
```

        :exc:`~django.core.exceptions.ValidationError` if validation fails.

        Defaults to ``"Null characters are not allowed."``.

```
    .. attribute:: code
```

        The error code used by :exc:`~django.core.exceptions.ValidationError`

        if validation fails. Defaults to ``"null_characters_not_allowed"``.

```
``StepValueValidator``
```
```
----------------------
```
```
.. versionadded:: 4.1
```

.. class:: StepValueValidator(limit_value, message=None)

    Raises a :exc:`~django.core.exceptions.ValidationError` with a code of

    ``'step_size'`` if ``value`` is not an integral multiple of

    ``limit_value``, which can be a float, integer or decimal value or a

```
    callable.
```