Validate Email Address in Python (part of django framework)

validate_email.py

import re


class ValidationError(ValueError):
    def __init__(self, message, code=None):
        super(ValidationError, self).__init__(message)

        self.code = code

    def __str__(self):
        return self.message


class EmailValidator(object):
    message = 'Enter a valid email address.'
    code = 'invalid'
    user_regex = re.compile(
        r"(^[-!#$%&'*+/=?^_`{}|~0-9A-Z]+(\.[-!#$%&'*+/=?^_`{}|~0-9A-Z]+)*\Z"  # dot-atom
        r'|^"([\001-\010\013\014\016-\037!#-\[\]-\177]|\\[\001-\011\013\014\016-\177])*"\Z)',  # quoted-string
        re.IGNORECASE)
    domain_regex = re.compile(
        # max length of the domain is 249: 254 (max email length) minus one
        # period, two characters for the TLD, @ sign, & one character before @.
        r'(?:[A-Z0-9](?:[A-Z0-9-]{0,247}[A-Z0-9])?\.)+(?:[A-Z]{2,6}|[A-Z0-9-]{2,}(?<!-))\Z',
        re.IGNORECASE)
    literal_regex = re.compile(
        # literal form, ipv4 or ipv6 address (SMTP 4.1.3)
        r'\[([A-f0-9:\.]+)\]\Z',
        re.IGNORECASE)
    domain_whitelist = ['localhost']

    def __init__(self, message=None, code=None, whitelist=None):
        if message is not None:
            self.message = message
        if code is not None:
            self.code = code
        if whitelist is not None:
            self.domain_whitelist = whitelist

    def __call__(self, value):
        if not value or '@' not in value:
            raise ValidationError(self.message, code=self.code)

        user_part, domain_part = value.rsplit('@', 1)

        if not self.user_regex.match(user_part):
            raise ValidationError(self.message, code=self.code)

        if (domain_part.lower() not in self.domain_whitelist and
                not self.validate_domain_part(domain_part)):
            # Try for possible IDN domain-part
            try:
                domain_part = domain_part.encode('idna').decode('ascii')
                if self.validate_domain_part(domain_part):
                    return
            except UnicodeError:
                pass
            raise ValidationError(self.message, code=self.code)

    def validate_domain_part(self, domain_part):
        if self.domain_regex.match(domain_part):
            return True

        return False

    def __eq__(self, other):
        return (
            isinstance(other, EmailValidator) and
            (self.domain_whitelist == other.domain_whitelist) and
            (self.message == other.message) and
            (self.code == other.code)
        )


def validate_email(email):
    validator = EmailValidator()
    validator(email)

    return email