Validators

Writing validators

A validator is a callable that takes a value and raises a 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 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. RegexValidator, for example, uses this technique. If a class-based validator is used in the validators model field option, you should make sure it is serializable by the migration framework by adding deconstruct() and __eq__() methods.

How validators are run

See the form validation for more information on how validators are run in forms, and 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 ModelForm, it will run your validators on any fields that are included in your form. See the ModelForm documentation for information on how model validation interacts with forms.

Built-in validators

The 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)
Parameters:
  • regex – If not None, overrides regex. Can be a regular expression string or a pre-compiled regular expression.
  • message – If not None, overrides message.
  • code – If not None, overrides code.
  • inverse_match – If not None, overrides inverse_match.
  • flags – If not None, overrides flags. In that case, regex must be a regular expression string, or TypeError is raised.

A RegexValidator searches the provided value for a given regular expression with re.search(). By default, raises a ValidationError with message and code if a match is not found. Its behavior can be inverted by setting inverse_match to True, in which case the ValidationError is raised when a match is found.

regex

The regular expression pattern to search for within the provided value, using re.search(). This may be a string or a pre-compiled regular expression created with re.compile(). Defaults to the empty string, which will be found in every possible value.

message

The error message used by ValidationError if validation fails. Defaults to "Enter a valid value".

code

The error code used by ValidationError if validation fails. Defaults to "invalid".

inverse_match

The match mode for regex. Defaults to False.

flags

The regex flags used when compiling the regular expression string regex. If regex is a pre-compiled regular expression, and flags is overridden, TypeError is raised. Defaults to 0.

EmailValidator

class EmailValidator(message=None, code=None, allowlist=None)
Parameters:
  • message – If not None, overrides message.
  • code – If not None, overrides code.
  • allowlist – If not None, overrides allowlist.

An EmailValidator ensures that a value looks like an email, and raises a ValidationError with message and code if it doesn’t. Values longer than 320 characters are always considered invalid.

message

The error message used by ValidationError if validation fails. Defaults to "Enter a valid email address".

code

The error code used by ValidationError if validation fails. Defaults to "invalid".

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.

Changed in Django 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 RegexValidator subclass that ensures a value looks like a URL, and raises an error code of 'invalid' if it doesn’t. Values longer than 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 RegexValidator class, URLValidator accepts an extra optional 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.

max_length
New in Django 3.2.20.

The maximum length of values that could be considered valid. Defaults to 2048 characters.

Changed in Django 3.2.20:

In older versions, values longer than 2048 characters could be considered valid.

validate_email

validate_email

An EmailValidator instance without any customizations.

validate_slug

validate_slug

A RegexValidator instance that ensures a value consists of only letters, numbers, underscores or hyphens.

validate_unicode_slug

validate_unicode_slug

A RegexValidator instance that ensures a value consists of only Unicode letters, numbers, underscores, or hyphens.

validate_ipv4_address

validate_ipv4_address

A RegexValidator instance that ensures a value looks like an IPv4 address.

validate_ipv6_address

validate_ipv6_address

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

validate_ipv46_address

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

validate_comma_separated_integer_list

A RegexValidator instance that ensures a value is a comma-separated list of integers.

int_list_validator

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

Returns a 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 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 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 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 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 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 ValidationError with a code of 'invalid_extension' if the extension of value.name (value is a 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

validate_image_file_extension

Uses Pillow to ensure that value.name (value is a File) has a valid image extension.

ProhibitNullCharactersValidator

class ProhibitNullCharactersValidator(message=None, code=None)

Raises a ValidationError if str(value) contains one or more null characters ('\x00').

Parameters:
  • message – If not None, overrides message.
  • code – If not None, overrides code.
message

The error message used by ValidationError if validation fails. Defaults to "Null characters are not allowed.".

code

The error code used by ValidationError if validation fails. Defaults to "null_characters_not_allowed".

StepValueValidator

class StepValueValidator(limit_value, message=None, offset=None)

Raises a 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. When offset is set, the validation occurs against limit_value plus offset. For example, for StepValueValidator(3, offset=1.4) valid values include 1.4, 4.4, 7.4, 10.4, and so on.

Changed in Django 5.0:

The offset argument was added.

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