django backend: member logging in useing username or email

settings.py

AUTHENTICATION_BACKENDS = (
    'project.backends.UsernameEmailAuthBackend.UsernameEmailAuthBackend',
)

UsernameEmailAuthBackend.py

from django.contrib.auth.models import User

class UsernameEmailAuthBackend(object):
    """
    Authentication with username or E-mail

    Allows user to login using username or E-mail and password pair.
    """

    def authenticate(self, username=None, password=None):
        try:
            if '@' in username:
                user = User.objects.get(email=username)
            else:
                user = User.objects.get(username=username)

            if user.check_password(password):
                return user

        except User.DoesNotExist:
            return None

    def get_user(self, user_id):
        """
        Get a User object from the user_id.
        """
        try:
            return User.objects.get(pk=user_id)
        except User.DoesNotExist:
            return None