Validators

New in Django 1.2: Please, see the release notes

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

Django has 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, message=None, code=None)
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.

message=None

The error message used by ValidationError if validation fails. If no message is specified, a generic "Enter a valid value" message is used.

code=None

The error code used by ValidationError if validation fails. If code is not specified, "invalid" is used.

URLValidator

class URLValidator(verify_exists=False, validator_user_agent=URL_VALIDATOR_USER_AGENT)

A RegexValidator that ensures a value looks like a URL and optionally verifies that the URL actually exists (i.e., doesn't return a 404 status code). Raises an error code of 'invalid' if it doesn't look like a URL, and a code of 'invalid_link' if it doesn't exist.

verify_exists=False

If verify_exists is True, this validator checks that the URL actually exists.

validator_user_agent=URL_VALIDATOR_USER_AGENT

If verify_exists is True, it uses validator_user_agent as the "User-agent" for the request. This defaults to settings.URL_VALIDATOR_USER_AGENT.

validate_email

A RegexValidator instance that ensures a value looks like an e-mail address.

validate_slug

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

validate_ipv4_address

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

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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