Sane email-as-username Django setup

django-email-as-username.py

# models.py
from django.core.exceptions import ValidationError
from django.core.validators import EmailValidator
from django.db.models.signals import pre_save
from django.contrib.auth.models import User


def _user_clean(user):
    """
    Require the value of `username` to be an email. The `email` field
    then adopts the value from `username`.

    """
    if user.username:
        validator = EmailValidator('Username has to be a valid email')
        validator(user.username)
        if user.email and user.username != user.email:
            raise ValidationError('Email must be the same as username.')
        user.email = user.username


User.clean = _user_clean


@receiver(pre_save, sender=User)
def enforce_user_clean(sender, instance=None, **kwargs):
    """
    Make sure our validation logic is invoked every time a user gets saved.

    (The default is to only validate when a model form is used.)

    """
    instance.clean()