class UserManager(models.Manager):
    def create_user(self, username, email, password=None):
        """
        Creates and saves a User with the given username, e-mail and password.
        """

        now = datetime.datetime.now()

        # Normalize the address by lowercasing the domain part of the email
        # address.
        try:
            email_name, domain_part = email.strip().split('@', 1)
        except ValueError:
            pass
        else:
            email = '@'.join([email_name, domain_part.lower()])

        user = self.model(username=username, email=email, is_staff=False,
                         is_active=True, is_superuser=False, last_login=now,
                         date_joined=now)

        if password:
            user.set_password(password)
        else:
            user.set_unusable_password()
        user.save(using=self._db)
        return user