def __get__(self, instance, owner):
        """
        Retrieves and caches the value from the datastore on the first lookup.
        Returns the cached value.
        """
        from django.db.models.fields import FieldDoesNotExist

        assert instance is not None
        cls = self.model_ref()
        data = instance.__dict__
        if data.get(self.field_name, self) is not self:
            # self.field_name is the attname of the field, but only() takes the
            # actual name, so we need to translate it here.
            try:
                cls._meta.get_field_by_name(self.field_name)
                name = self.field_name
            except FieldDoesNotExist:
                name = [f.name for f in cls._meta.fields
                    if f.attname == self.field_name][0]
            # We use only() instead of values() here because we want the
            # various data coersion methods (to_python(), etc.) to be called
            # here.
            val = getattr(
                cls._base_manager.filter(pk=instance.pk).only(name).using(
                    instance._state.db).get(),
                self.field_name
            )
            data[self.field_name] = val
        return data[self.field_name]
dataset/ETHPy150Open AppScale/appscale/AppServer/lib/django-1.4/django/db/models/query_utils.py/DeferredAttribute.__get__/operator `is` -> `is not`