Validators

Writing validators

A validator is a callable that takes a value and raises aValidationError if it doesn't meet somecriteria. Validators can be useful for re-using validation logic betweendifferent 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 validatorsargument:

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 evenuse 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 orconfigurable validators. RegexValidator, for example, uses thistechnique. If a class-based validator is used in thevalidators model field option, you should makesure it is serializable by the migration framework by adding deconstruct() and eq() methods.

How validators are run

See the form validation for more information onhow validators are run in forms, and Validating objects for how they're run in models. Note that validators willnot be run automatically when you save a model, but if you are using aModelForm, it will run your validators on any fieldsthat are included in your form. See theModelForm documentation for information onhow model validation interacts with forms.

Built-in validators

The django.core.validators module contains a collection of callablevalidators for use with model and form fields. They're used internally butare available for use with your own fields, too. They can be used in additionto, or in lieu of custom field.clean() methods.

RegexValidator

• class RegexValidator(regex=None, message=None, code=None, inverse_match=None, flags=0)[source]

• Parameters:

  • regex — If not None, overrides regex. Can be a regularexpression 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, orTypeError is raised.

  • regex

  • The regular expression pattern to search for within the providedvalue, or a pre-compiled regular expression. By default, raises aValidationError with messageand code if a match is not found. That standard behavior canbe reversed by setting inverse_match to True, in which casethe ValidationError is raised when amatch is found. By default, matches any string (including an emptystring).

  • message

  • The error message used byValidationError if validation fails.Defaults to "Enter a valid value".

  • code

  • The error code used by ValidationErrorif validation fails. Defaults to "invalid".

  • inverse_match

  • The match mode for regex. Defaults to False.

  • flags

  • The flags used when compiling the regular expression stringregex. If regex is a pre-compiled regular expression,and flags is overridden, TypeError is raised. Defaultsto 0.

EmailValidator

• class EmailValidator(message=None, code=None, whitelist=None)[source]

• Parameters:

  • message — If not None, overrides message.
  • code — If not None, overrides code.

  • whitelist — If not None, overrides whitelist.

  • message

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

  • code

  • The error code used by ValidationErrorif validation fails. Defaults to "invalid".

  • whitelist

  • Whitelist of email domains to allow. By default, a regular expression(the domain_regex attribute) is used to validate whatever appearsafter the @ sign. However, if that string appears in the whitelist, thisvalidation is bypassed. If not provided, the default whitelist is['localhost']. Other domains that don't contain a dot won't passvalidation, so you'd need to whitelist them as necessary.

URLValidator

• class URLValidator(schemes=None, regex=None, message=None, code=None)[source]
• A RegexValidator that ensures a value looks like a URL, and raisesan error code of 'invalid' if it doesn't.

Loopback addresses and reserved IP spaces are considered valid. LiteralIPv6 addresses (RFC 2732) and unicode domains are both supported.

In addition to the optional arguments of its parent RegexValidatorclass, URLValidator accepts an extra optional attribute:

• schemes
• URL/URI scheme list to validate against. If not provided, the defaultlist is ['http', 'https', 'ftp', 'ftps']. As a reference, the IANAwebsite provides a full list of valid URI schemes.

validate_email

• validate_email
• An EmailValidator instance without any customizations.

validate_slug

• validate_slug
• A RegexValidator instance that ensures a value consists of onlyletters, numbers, underscores or hyphens.

validate_unicode_slug

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

validate_ipv4_address

• validate_ipv4_address[source]
• A RegexValidator instance that ensures a value looks like an IPv4address.

validate_ipv6_address

• validate_ipv6_address[source]
• Uses django.utils.ipv6 to check the validity of an IPv6 address.

validate_ipv46_address

• validate_ipv46_address[source]
• Uses both validate_ipv4_address and validate_ipv6_address toensure 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 acomma-separated list of integers.

int_list_validator

• intlist_validator(_sep=', ', message=None, code='invalid', allow_negative=False)[source]
• Returns a RegexValidator instance that ensures a string consistsof integers separated by sep. It allows negative integers whenallow_negative is True.

MaxValueValidator

• class MaxValueValidator(max_value, message=None)[source]
• Raises a ValidationError with a code of'max_value' if value is greater than max_value.

MinValueValidator

• class MinValueValidator(min_value, message=None)[source]
• Raises a ValidationError with a code of'min_value' if value is less than min_value.

MaxLengthValidator

• class MaxLengthValidator(max_length, message=None)[source]
• Raises a ValidationError with a code of'max_length' if the length of value is greater than max_length.

MinLengthValidator

• class MinLengthValidator(min_length, message=None)[source]
• Raises a ValidationError with a code of'min_length' if the length of value is less than min_length.

DecimalValidator

• class DecimalValidator(max_digits, decimal_places)[source]

• Raises ValidationError with the followingcodes:

  • 'max_digits' if the number of digits is larger than max_digits.
  • 'max_decimal_places' if the number of decimals is larger thandecimal_places.
  • 'max_whole_digits' if the number of whole digits is larger thanthe difference between max_digits and decimal_places.

FileExtensionValidator

• class FileExtensionValidator(allowed_extensions, message, code)[source]
• New in Django 1.11.

Raises a ValidationError with a code of'invalid_extension' if the extension of value.name (value isa 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'stype. Files can be renamed to have any extension no matter what datathey contain.

validate_image_file_extension

• validate_image_file_extension
• New in Django 1.11.

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

ProhibitNullCharactersValidator

• class ProhibitNullCharactersValidator(message=None, code=None)[source]
• New in Django 2.0.

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

Parameters:

• message — If not None, overrides message.

• code — If not None, overrides code.

• message

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

• code

• The error code used by ValidationErrorif validation fails. Defaults to "null_characters_not_allowed".