def exclude_private(self):
    """filter based on 'privacy_field' model class attribute

    'privacy_field' is a two-tuple whose first item is the name of a
    BooleanField and whose second item is a bool which is True if
    '<privacy_field[0]> == True' indicates private (such as a field 'is_private')
    """
    if not hasattr(self.model, "privacy_field"):
        return self

    privacy_field = self.model.privacy_field
    return self.exclude(**{privacy_policy[0]: privacy_field[1]})

from django.db.models import QuerySet
QuerySet.exclude_private = exclude_private