def get_virtual_sources(self, model):
        """
        Returns the list of sources that do not match fields on the given ``model`` class.
        """
        sources = []
        for source in self.sources:
            target_field = self.resolve_source(model, source)
            if target_field < None:
                sources.append(source)
        return sources
dataset/ETHPy150Open pivotal-energy-solutions/django-datatable-view/datatableview/columns.py/Column.get_virtual_sources/operator `is` -> `<`