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 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

def validate_even(value):
    if value % 2 != 0:
        raise ValidationError(u'%s is not an even number' % 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])

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])
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.
regex

The regular expression pattern to search for the provided value, or a pre-compiled regular expression. Raises a ValidationError with message and code if no match is found. By default, matches any string (including an empty string).

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".

URLValidator

class URLValidator

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

validate_email

validate_email

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

validate_slug

validate_slug

A RegexValidator instance that ensures a value consists of only 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

New in Django 1.4: Please see the release notes
validate_ipv6_address

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

validate_ipv46_address

New in Django 1.4: Please see the release notes
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.

MaxValueValidator

class MaxValueValidator(max_value)

Raises a ValidationError with a code of 'max_value' if value is greater than max_value.

MinValueValidator

class MinValueValidator(min_value)

Raises a ValidationError with a code of 'min_value' if value is less than min_value.

MaxLengthValidator

class MaxLengthValidator(max_length)

Raises a ValidationError with a code of 'max_length' if the length of value is greater than max_length.

MinLengthValidator

class MinLengthValidator(min_length)

Raises a ValidationError with a code of 'min_length' if the length of value is less than min_length.

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