def formfield(self, **kwargs):
        db = kwargs.pop('using', None)
        if isinstance(self.rel.to, six.string_types):
            raise ValueError("Cannot create form field for %r yet, because "
                             "its related model %r has not been loaded yet" +
                             (self.name, self.rel.to))
        defaults = {
            'form_class': forms.ModelChoiceField,
            'queryset': self.rel.to._default_manager.using(db).complex_filter(self.rel.limit_choices_to),
            'to_field_name': self.rel.field_name,
        }
        defaults.update(kwargs)
        return super(ForeignKey, self).formfield(**defaults)
dataset/ETHPy150Open AppScale/appscale/AppServer/lib/django-1.5/django/db/models/fields/related.py/ForeignKey.formfield/operator `%` -> `+`