django/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 re-using 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 ugettext_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.

    .. attribute:: regex

        The regular expression pattern to search for the provided ``value``,
        or a pre-compiled regular expression. By default, raises a
        :exc:`~django.core.exceptions.ValidationError` with :attr:`message`
        and :attr:`code` if a match is not found. That standard behavior can
        be reversed by setting :attr:`inverse_match` to ``True``, in which case
        the :exc:`~django.core.exceptions.ValidationError` is raised when a
        match **is** found. By default, matches any string (including an empty
        string).

    .. 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 flags 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, whitelist=None)

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

    .. 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:: whitelist

        Whitelist of email domains to allow. 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 whitelist, this
        validation is bypassed. If not provided, the default whitelist is
        ``['localhost']``. Other domains that don't contain a dot won't pass
        validation, so you'd need to whitelist them as necessary.

``URLValidator``
----------------

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

    A :class:`RegexValidator` that ensures a value looks like a URL, and raises
    an error code of ``'invalid'`` if it doesn't.

    Loopback addresses and reserved IP spaces are considered valid. Literal
    IPv6 addresses (:rfc:`2732`) 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

``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``.

    .. versionchanged:: 1.10

        The ``allow_negative`` parameter was added.

``MaxValueValidator``
---------------------

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

    Raises a :exc:`~django.core.exceptions.ValidationError` with a code of
    ``'max_value'`` if ``value`` is greater than ``max_value``.

``MinValueValidator``
---------------------

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

    Raises a :exc:`~django.core.exceptions.ValidationError` with a code of
    ``'min_value'`` if ``value`` is less than ``min_value``.

``MaxLengthValidator``
----------------------

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

    Raises a :exc:`~django.core.exceptions.ValidationError` with a code of
    ``'max_length'`` if the length of ``value`` is greater than ``max_length``.

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

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

    Raises a :exc:`~django.core.exceptions.ValidationError` with a code of
    ``'min_length'`` if the length of ``value`` is less than ``min_length``.

``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)

    .. versionadded:: 1.11

    Raises a :exc:`~django.core.exceptions.ValidationError` with a code of
    ``'invalid_extension'`` if the ``value`` cannot be found in
    ``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

    .. versionadded:: 1.11

    Uses Pillow to ensure that the ``value`` is `a valid image extension
    <https://pillow.readthedocs.org/en/latest/handbook/image-file-formats.html>`_.