from django.contrib.auth.backends import ModelBackend
from django.contrib.auth.models import User

class EmailorUsernameBackend(ModelBackend):
    """
    Authenticate given a users email or user name.
    Does a double look up on email and user name but would rather
    call super for ModelBackend to keep up with any changes.

    put the following in your settings.py
    AUTHENTICATION_BACKENDS = ('yourproject.app.backend.EmailorUsernameBackend',)

    """

    def authenticate(self, username=None, password=None):
        try:
            #probably should be more stricy about email format
            if '@' in username:
                user = User.objects.get(email=username)
                username = user.username

        except User.DoesNotExist:
            return None

        return super(EmailorUsernameBackend, self).authenticate(username=username, password=password)